Thank you all for participating in today's call. Earlier today, iRhythm released financial results for the first quarter ended March 31st, 2022. Before we begin, I'd like to remind you that management will make statements during this call that include forward-looking statements within the meaning of federal securities laws pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Any statements contained in this call that are not statements of historical fact should be deemed to be forward-looking statements. These are based upon our current estimates and various assumptions and reflect management's intentions, beliefs, and expectations about future events, strategies, competition, products, operating plans, and performance. These statements involve risks and uncertainties that could cause actual results or events to materially differ from those anticipated or implied by these forward-looking statements. Accordingly, you should not place undue reliance on these statements.
For a list and description of the risks and uncertainties associated with our business, please refer to the Risk Factors section of our most recent annual and quarterly reports on Form 10-K and Form 10-Q, respectively, filed with the SEC. Also, during the call, we will discuss certain financial measures that have not been prepared in accordance with U.S. GAAP with respect to our non-GAAP and cash-based results, including adjusted EBITDA, adjusted operating expenses, and adjusted net loss. Unless otherwise noted, all references to financial metrics are presented on a non-GAAP basis. The presentation of this additional information should not be considered in isolation of and a substitute for or superior to results prepared in accordance with GAAP. Please refer to the tables in our earnings release and 10-Q for a reconciliation of these measures to their most directly comparable GAAP financial measures.
This conference call contains time-sensitive information and is accurate only as of the live broadcast today, May 5th, 2022. iRhythm disclaims any intention or obligation, except as required by law, to update or revise any financial projections or forward-looking statements, whether because of new information, future events, or otherwise. With that, I'll turn the call over to Quentin Blackford, iRhythm's President and CEO.
Thank you, Leigh. Good afternoon, and thank you all for joining us. Douglas Devine, our Chief Operating Officer and Chief Financial Officer, and Daniel Wilson, our EVP of Corporate Strategy and Development, join me on today's call. My prepared remarks today cover progress we've made throughout the first portion of 2022 and discuss the near- and long-term growth initiatives for our business. I'll then turn the call over to Douglas to provide a detailed review of our first quarter financial results, as well as our updated guidance for 2022. Our first quarter results came in ahead of expectations across the board and demonstrate the value of an increased focus and discipline that we are driving into the business.
We were pleased with our first quarter revenue performance growing by 24% year-over-year to $92 million, fueled by strong unit volume growth as well as the benefit of the improved Novitas pricing that went into effect January first. Furthermore, we were pleased with the improved operational discipline and efficient management of cost, resulting in improved gross margin and lower than anticipated spending. As a result, we are providing favorable updates to both our revenue and profitability expectations for the year, which Douglas will share in a bit. We continue to make progress on the reimbursement front as we realized another positive step forward as NGS, the MAC that serves our suburban Chicago area and where one of our primary independent diagnostic testing facilities, or IDTFs, is located.
They updated their payment rates to approximately $329 and $342 for the two main CPT codes that we use in our business, effective April 1st. We are pleased with this most recent update provided by NGS, which continues to demonstrate that the cost associated with delivering the Zio XT service and the value that it provides are being better understood. We will continue to engage with the other regional MACs on their internal review processes and will provide updates as appropriate. As it relates to national pricing, we expect that CMS will release its 2023 Medicare Physician Fee Schedule proposed rule in or around July of this year.
This will be followed by an open comment period and final rulings, which have historically been communicated in the November timeframe and would then be effective January 1st, 2023. We are continuing to fully participate and coordinate with our industry partners, stakeholders, customers, and medical societies on this process to establish fair and stable national CMS pricing for Zio XT moving forward, which we are confident can lead to increased access and improving care for all. We believe Zio offers the most complete ambulatory cardiac monitoring solution backed by the most advanced AI in the space, so that providers can accurately diagnose patients more quickly and efficiently. We also took additional steps forward in building our leadership team, announcing last week that Dr. Mintu Turakhia will be joining iRhythm in the newly created role of Chief Medical Officer and Chief Scientific Officer.
Mintu was one of the early adopters of Zio and performed one of the first-ever silent AF studies with Zio. In addition to his clinical work, Mintu was the co-founder of the Stanford Center for Digital Health and is a seasoned operator who has led the development of virtual care and remote patient monitoring software for clinical trials, academic research, and commercialized healthcare products. Mintu will be responsible for guiding our innovation efforts and leading our research and evidence generation. I'm personally thrilled to have Mintu on board and look forward to having him hit the ground running. Coming back to the business performance, within our core U.S. market, we saw strong unit volumes and pricing performance during the quarter. Registrations rebounded nicely to record levels in March after a slow start to January due to the impact of the Omicron variant.
We also saw continued momentum within new accounts as the number of new account openings were up 15% from the fourth quarter of 2021. While we were very pleased with the strength that we saw exiting March, we believe some of that strength may have been attributable to patient backlogs from December and January. We continue to believe that Zio should be the gold standard in ambulatory cardiac monitoring, and the opportunity ahead of us in this core market alone is immense. Approximately 5.6 million ambulatory cardiac monitoring tests are prescribed annually in the U.S., but we estimate that less than 25% of those are for our clinically superior extended wear monitors.
Our data-driven AI and deep learned algorithms are a significant differentiator from competitors, and we see ourselves increasingly as a provider of insights to our patients and customers within the larger digital health ecosystem. As part of this, we believe that our core market will only expand over time as we create new opportunities to impact prediction and prevention of disease, move deeper into primary care, and expand into additional use cases. The clinical superiority of Zio remains a key reason we continue to increase our market share, and we are pleased to see the mounting clinical evidence continue to grow and further demonstrate how our innovative technology can be leveraged for the benefit of patients, clinicians, and patient care networks.
At the recent ACC meeting in Washington, DC, as well as the HRS conference in San Francisco this past weekend, we saw important clinical data presented highlighting Zio AT, Zio XT, and the Zio Watch. For Zio AT, research presented at ACC highlighted that monitoring with post-TAVR discharge can identify AFib, high degree AV block, and supraventricular tachycardia in patients who are at risk for arrhythmic disorders. The results found the presence of AFib in nearly 25% of the study population, including the younger cohort within the study. Separately, data was also presented that demonstrated Zio AT was safely able to monitor and aid in the diagnosis of patients upon discharge from the ER, thus avoiding a hospital stay. This study estimated that the use of Zio AT saved this healthcare system approximately 136 inpatient hospitalization days.
With Zio XT, we recently presented additional data that further supports movement into the asymptomatic and undiagnosed AFib market. Top line data from the GUARD-AF study showed that the Zio service is a viable solution for the early detection and diagnosis of silent atrial fibrillation in moderate risk populations. Within the study, nearly 5% of the population had AFib detected within two weeks of monitoring. This further highlights the need to help undiagnosed populations effectively seek treatment before more serious problems can occur, therefore improving patient outcomes. Finally, at the recent HRS conference this past weekend, we announced exciting data on the Zio Watch demonstrating our ability to detect arrhythmias using non-patch-based technology.
The findings from our first prospective study were designed to evaluate the performance of the Zio Watch's PPG sensor and AFib Context Engine algorithm in detecting irregular rhythms in those at risk with having AFib. The data revealed that interval level sensitivity and specificity of our proprietary algorithm were comparable to our Zio XT patch. Moreover, PPG-derived AFib burden from the Zio Watch was an accurate measure when compared to the Zio XT as a reference. The Zio Watch and the AI algorithms it uses are currently under 510(k) review by the FDA and pending clearance. In addition to the further pursuit of clinical evidence demonstrating the value of Zio, we are also committed to innovation. Underscoring that commitment, we are very pleased to announce that we have shipped the first batch of our next generation biosensor, the Zio monitor, for first patient use following regulatory clearance.
This monitor will eventually replace Zio XT while providing a platform that delivers a dramatically smaller form factor, resulting in an improved patient experience and a reduced cost profile with greater efficiencies for manufacturability and scalability without sacrificing our quality of service. Full-scale commercialization and conversion of this next generation device is anticipated in 2023. Shifting to our strategy of international expansion, our goal is to establish Zio as a standard of care in international markets, much as we are doing in the U.S. We have been working on a strategic pathway towards continued commercial expansion in the U.K. and introduction into other countries over the next two to three years. Within the U.K., we continue to execute against the NHSX AI award in select NHS sites, as well as grow our business within the private payer market.
We expect to use the remaining portion of the AI award within 2022 and are working with individual NHS sites to secure local funding and ensure continued access to Zio while we continue our efforts to secure sustainable reimbursement within the NHS. In the meantime, we expect our UK business to grow more moderately. Beyond the UK, we are excited to announce that we will be commencing market access initiatives in Germany, France, the Netherlands, and Sweden in the coming months, adding roughly 1.7 million ambulatory cardiac monitoring tests to our addressable market. As mentioned previously, we are also excited about the Japanese market, where there are more than 1.5 million ambulatory cardiac monitoring tests prescribed annually.
We anticipate initiating the reimbursement and regulatory pathways within the next few months, which would put us on a timeline for commercial launch by the first half of 2024. We continue to believe there's a large opportunity to bring Zio into international markets and are accelerating our efforts to initiate market access and commercial introduction. We look forward to sharing our milestones as these efforts progress. Turning to our strategy of expansion into adjacent markets, as noted earlier, we saw additional clinical data presented that further supports the move into the asymptomatic and undiagnosed AFib market. To capture this opportunity, we are building a targeted detection program and capability that will allow us to deliver a compelling product to payers as well as an engaging experience to undiagnosed and underserved patient populations.
We are fully committed to providing access to valuable digital health tools to all patients who could benefit from them. By harnessing the power of data-driven, deep learned AI, we believe we can redefine the standard of care with earlier insights that predict and prevent disease. Our efforts with asymptomatic AF align well with these goals, and we look forward to sharing more details on these initiatives and other growth strategies at an investor day later this year. In closing, we have started 2022 very strong and are very confident in the sizable opportunities ahead of us to serve millions more patients. We see tremendous runway for growth within the core market that we serve today as we continue to shift the standard of care to Zio, the gold standard in this space.
We continue to invest in our mid and long-term growth initiatives that will leverage our technology platform into new geographies and new markets. I have never been more excited about the future that I see at iRhythm, and we are intently focused on realizing our vision. I'll now turn the call over to Douglas.
Thanks, Quentin. Our first quarter 2022 financial results demonstrated the strength of our business as revenue grew 24% year-on-year, 13% quarter-on-quarter. Registrations and new account onboarding continued solid growth, and new account sales again contributed strongly to our growth. Although the economic environment remains uncertain, we are pleased with the way 2022 has started. Taking a more detailed look at our first quarter financial results on a sequential basis, revenue increased 13% quarter-on-quarter from $82 million to $92 million. Growth in our average daily registrations was strong, increasing by about 13% during the first quarter as compared to 7% during the fourth quarter. We had strong growth in the number of new accounts onboarded, increasing by 15% from Q4 2021 to Q1 2022.
Looking at new store, same-store mix, new store, defined as accounts that have been open for less than 12 months, accounted for 55% of our year-over-year unit growth, up from 46% in the fourth quarter of 2021. Home enrollment was at 21% in the first quarter, flat from Q4 2021 levels. Turning our attention to the rest of the P&L, gross margin for the first quarter was 66.9%, a 4.2% increase from the gross margin of 62.7% in Q4 of 2021. Increases in volume and average selling prices, coupled with a reduction in average unit cost all contributed to the increased gross margin during Q1 2022 versus Q4 of 2021.
For the first quarter, operating expenses excluding restructuring were $83.7 million, flat compared to Q4 of 2021 and up 7% year over year. Sequentially, hiring and compensation expenses during the quarter were offset by milestone expenses to Verily that did not reoccur in Q1. We expect the next Verily milestone to occur in 2023. During Q1, we incurred $26.6 million in restructuring charges, primarily associated with a reduction in size of our San Francisco facility to better align the company to the new remote working environment. Adjusted EBITDA of -$4.8 million in Q1 2022 was up $12.5 million compared to Q4 2021 adjusted EBITDA of -$17.3 million. Cash and short-term investments declined $30.3 million from the fourth quarter of 2021 to $208.8 million.
2021 bonus payment, payroll taxes, 401(k) contribution, working capital, and adjusted EBITDA losses consumed cash in the first quarter, partially offset by the initial loan drawdown with Silicon Valley Bank on our amended debt facility. Accounts receivable increased by $8.9 million to $55.3 million from $46.4 million in Q4 2021, primarily driven by quarter-on-quarter increase in revenue. Adjusted net loss, which excludes restructuring related expenses, was -$23.7 million or a loss of $0.80 per share, compared with a net loss of -$27.8 million or $0.95 per share for the same period of the prior year. Finally, we amended our existing debt facility with Silicon Valley Bank to improve upon the pricing and terms of our prior facility.
The amended credit facility is non-dilutive and consists of a term loan of up to $75 million and a revolving credit facility of up to $25 million. $35 million in the term loan was drawn down at closing to pay in full the approximately $18.5 million outstanding on the term loan under the prior credit facility and to fund working capital. The remaining $40 million of the term loan will remain available for us to draw through December 31st, 2023, subject to applicable conditions. The revolving credit line availability is subject to a borrowing base comprised of our accounts receivable. The amended credit facility will mature March 1, 2027.
Turning to guidance for 2022, we are increasing our expectation for full year revenue to range between $410 million and $420 million, reflecting year-over-year growth of 27%-30%. The increase in our guidance reflects our performance in the first quarter of 2022, as well as a positive impact from the updated NGS pricing. As we currently have an IDTF in suburban Chicago, we expect to see a small positive impact to revenue starting in the second quarter and increasing into the second half of the year. We expect gross margin to be between 68%-69% for the full year 2022. We expect adjusted operating expenses in the range of $375 million and $385 million, flat to our prior guidance.
We expect adjusted EBITDA to range between -$15 million and -$25 million. Our adjusted EBITDA for 2022 will exclude restructuring costs and stock compensation. With that, Quentin, Daniel, and I would like to now open the call for questions. Operator?
Thank you. We will now begin our question-and-answer session. If you have a question, please press zero, then one on your touch tone phone. If you wish to be removed from the queue, please press zero then two. If you're using a speakerphone, please pick up the handset first before pressing the numbers. Once again, if you have a question, please press zero then one on your touch tone phone. We have our first question from Allen Gong with JP Morgan.
Hey, guys, this is Allen. Congrats on the good quarter. I guess, you know, first question I really had is on the reimbursement change. You know, it's definitely welcome to see, but with, you know, in theory, a proposed rule and potentially a national rate decision from CMS, expected in a couple of months, you know, why would they, I guess, go ahead and make this kind of change? I guess what were their reimbursement rates previously?
Hey, Alan. This is Quentin here. You know, I think we've been working with the MACs from really in the mid part of last year, and this is a continuation of that process. It's not just NGS, it's all of the MACs. You know, we've been pretty deliberate around the fact that we need to continue to work with them from a strategic perspective being that you know, we believe there will be a final rule, and we're hoping for a final rule. We want the final rule as it increases access to care for all. But in the case that there's not a final rule, we need to continue to articulate and demonstrate the value that we can deliver through our offering to each one of these MACs.
Not only does our work continue with NGS as it did, and we saw a nice rate, but it continues with all of the MACs at this point, continuing just to put ourselves in a position where we're ready, really no matter what the alternative is with the final rule. This is much more of a strategic pathway forward and incredibly pleased to see the outcome with it. I think it continues to demonstrate that when the parties get to the table and get around the information, the cost data that is being presented, they see very clearly what it takes to put this sort of technology and capability into the marketplace, and it gets recognized, it gets valued. Incredibly pleased with them.
Obviously, a rate of 340 is, you know, continuing to step north of the 230 rate that Novitas was at, and they all were looking at similar data sets, so continuing to sort of look at the overall cost profile of it. It was a meaningful step up from where they had been historically. I think for us, what's most encouraging is it's put right within a jurisdiction where we already have an IDTF that lets us become much more efficient and effective with how we utilize our resources to serve this marketplace. From many different angles, it hits on the strategic asset or aspect of what we're trying to achieve. Incredibly pleased.
Got it. That obviously didn't contribute to the outperformance you saw in the quarter. You know, unfortunately, I think the webcast and the call might have been having some issues in the first five-10 minutes, so apologies if you went over this. Just what really drove that outperformance in the first quarter, and then when we think about the fact that, you know, your guidance is a step above that, some of that to reflect not the CMS, the MAC reimbursement rate increase and some of that to reflect, you know, hope for that momentum continuing, if you could give us a little bit of a breakdown there. Thank you very much.
Sure. Apologies for the first part of the call. We weren't getting that on our side. For those of you who missed out on that, apologies, and we'll make sure that clearly the transcript is out there and you're able to get it. You know, when you look at the first quarter, the back end of the quarter was incredibly strong. We touched on the fact that March were record daily registrations for us in the prepared remarks, which is a significant rebound coming off of the slow start in January, early February as a result of the Omicron variant. You know, how much of March was pent-up demand versus true underlying strength is yet to be decided. We continue to be, you know, encouraged by the results that we saw into April. So we're pleased from that perspective.
From a guidance perspective, we didn't wanna get ahead of ourselves. How we thought about that was more or less passing through the beat of the first quarter, which call it roughly $3 million or so, and then increasing for the impact that we believe we can get from the NGS reimbursements over the remainder of the year, which is really gonna be in the back half by the time we're able to get the resources utilized the way we want to. That adds the other, call it roughly $7 million or so of benefit that gets you to the full $10 million raise on both the low and high end.
Thank you. Our next question is from Joanne Wuensch with Citi.
Good afternoon. This is Anthony on for Joanne. Thank you for taking our questions, and congrats on a really good quarter. Just on gross margins, they compressed year-over-year, which I think was expected. Just given that you raised guidance for them, and you have some new products coming on with the watch and sensor, can you just talk about how you're thinking about margins for the rest of the year? Thanks.
Yeah. Douglas, why don't you jump on that one?
Sure. Thanks, Quentin.
When you look at the slight depression on the gross margins, you know, we've added a lot of capacity, particularly on the clinical side, and that added capacity is still coming up to full productivity. As you look forward, you know, this is consistent with the message we gave you in Q1, that we're gonna build throughout the year, that we're expecting Q4 gross margins to be north of 70% and to see a gradual step function move up in gross margin as we move throughout the year. Some of that's gonna be volume, some of that's gonna be, you know, digesting the capacity increases that we've put into the company.
You're gonna see the same thing on the EBITDA side where, you know, again, we're expecting to be at breakeven or slightly positive on adjusted EBITDA in the fourth quarter and making steady progress as we move throughout the year. In regards to the new monitor, first, that's not going to launch in larger commercial volumes until 2023. Second, I wouldn't expect that one to be a big mover on the gross margin.
That's helpful. If I could just ask one more. What is your outlook on private reimbursement? Do you expect it to sort of stay stable or down low single digits? Would just like to know your thoughts. Thanks.
Yeah, we continue to be, you know, encouraged with what we see in the private commercial reimbursement space. You know, I think that those payers tend to take a bit of a different perspective and different look at at how to value this technology. I think they understand that having a better capability to diagnose earlier in the care pathway and reduce downstream costs, when they can see that clearly, they're willing to pay for it. We've seen that reflected in our negotiations with the payers. I think the continual move with the MACs, the recent NGS rate, for example, I think it is just another good data point to put out there that when you get into the data and understand the value that this delivers, the reimbursed value is reflected in that.
We were encouraged with NGS, and I think that plays well with us in terms of the discussions with the commercial payers. I will tell you, there's not been anything in those commercial discussions that give us concern around commercial rates at this point in time, and those conversations have been pretty steady for the last, you know, nine months or so.
We have our next question from Margaret Kaczor with William Blair.
Hey, guys, this is Maggie Boeye on for Margaret. Thanks for taking our questions. I wanted to ask one on the Verily or the Zio Watch. So I heard you guys say that it's pending 510(k) approval, so just wanted to see if you could provide any updates on that pathway to approval and then any more updates on the business model.
Yeah. Daniel, do you wanna jump in and take this one on the watch?
Yeah, sure. I'd be happy to. Yeah, thanks for the question, Maggie. It is still with the FDA. We're, as we've noted previously, FDA timelines are a bit harder to predict at the moment due to COVID. It is with the FDA, and we're hoping for clearance here in the near term, and we'll certainly update folks once we hit that milestone. From there, we will be entering a market evaluation phase in the early part of next year, assuming we get clearance this year. We'll be exploring that business model and various use cases.
I'd say more to share once we get certainly to the milestone of clearance, and then as we're getting into next year and launching into that market evaluation phase, we'll be sharing more with everyone.
Got it. Thank you. I just wanted to ask a more high-level question here. You guys have had, you know, several years of strong growth and are headed towards your next leg of the adoption curve. What's the white space left for you guys here? Obviously, you know, there's a lot left to capture. What are you targeting in 2022 and 2023 to drive the next leg of growth? Thank you.
Yeah, terrific question, and excited to answer that because I think there are so many different growth pathways that sit in front of the company. One of the most significant opportunities and near-term opportunities continues to be the awareness and the adoption of the technology in this core market that we serve right here in the States. You know, less than 25% of the market utilizes extended wear patch technology and for the most part continues to utilize the older, you know, traditional Holter monitor, which we know is just not a very good solution.
There's such an improvement out there with the Zio that we believe it should be the standard of care and the gold standard in this space, and that ultimately, you know, we're gonna see market adoption move to that 75%-80% of volumes over time. That gives you a lot of runway in this core market alone, which has us excited. I think you then think about being able to move into the primary care space, which we know, you know, even more folks than the 5.6 million ACM tests that are prescribed every year, call it closer to eight million people show up in the primary care space with palpitations. With the ease of use around the product, it's easy to believe that we ought to see the market be able to expand.
I get encouraged from that perspective, and you're gonna see us really focus in on getting after those opportunities. You know, even within the core market, just an interesting data point, we call on less than 50% of the cardiologists and EP accounts in the States today. There's still a lot of greenfield opportunity just in the specialist area of the US core market, but then you have got the primary care that comes behind it. I think for the next couple of years, you're gonna hear us talk a lot about just really refining our focus, our discipline of calling on those accounts. Increasing visibility into it and really creating awareness and education to convert what sits in front of us in the core market.
You know, beyond that, and we've talked about this, the opportunity to take this technology into the international space is real. There's no reason why the international markets aren't enjoying the same sort of benefit that this product and technology can deliver, like we're seeing right here in the States. We're excited to announce that we've identified kind of the next four key countries within the European region, being Germany, France, Netherlands, and Sweden, which add another 1.7 million of addressable market for us, that we're excited about. There's a lot of growth sitting in front of us just in this core market and the international sort of symptomatic market that I think will deliver very nice growth results for us.
In the meantime, we'll continue to explore some of the adjacent opportunities that can only add to the addressable market over time. Our focus is in this core market right now.
Great. Thanks so much.
We have our next question from David Rescott with Truist Securities.
Hey, guys. Thanks for taking the question, and congrats on a good start to the year. I wanted to start first on the updated rate with the Chicago MAC. I just want to make sure I'm understanding that correctly. You mentioned a little bit how you're able to maybe optimize some of the services here. I mean, is this something that you can, you know, in a sense, kind of reroute maybe the patients that you otherwise, you know, or CMS patients that otherwise may have gone through the Houston MAC now potentially going through this higher rate MAC in Chicago since you do have an IDTF there? Just as a second part to that, you know, how does this at all impact the way that you were thinking about the NCD for 2023?
Can you repeat the second part of that question, David?
Yeah. Just how, if at all, this does or does not impact the way that you are thinking about the NCD for 2023?
Got it. Look, I think for us, one of the most exciting aspects of getting the rate adjusted with the MAC where we have an IDTF is the better ability to utilize our resources. You know, we've been somewhat constrained in terms of just how we can drive the efficient use of those resources historically as CMS was being you know, the Medicare claims were being processed through the Houston MAC. Absolutely, there becomes that opportunity to become much more efficient overnight. We've got to get the resources, you know, in place and the systems in place to make sure we do this right and it's a good experience for the patients. At the same time, the opportunity sits there to be more efficient and then, yeah, you're gonna get the benefit of the higher rate.
The way you described it is the right way to think about it. That is how we will get that benefit. In terms of 2023, yeah, I think it gives us the opportunity to really think about resource utilization in the best way possible, the most efficient way possible for the company. If we can get that CMS final rate put in place at a reasonable rate, then we feel very good about being most efficient with our resources. I do think it leads into an opportunity, you know, for us as we think about 2023 just to be the most efficient, you know, operation that we can be.
Okay. That's helpful. I guess kind of a quick follow-up to that, but also a second question. I think, you know, the guidance or the prior guidance for the year, you had mentioned maybe Q1 would be around 20%-22% of revenue. If you think about that relative to the guide now, that implies that you are at the upper end of the range if we think about Q1 being this 22% of revenue for the full year. So I guess one, you know, is the raise here, just trying to get some color on what the raise was driven by here. I mean, is this in part volume, or does the Chicago rate impact that at all?
If so, how soon, I think, do you think that you'd be able to kinda optimize this Chicago IDTF with the higher rate?
Douglas, do you wanna jump on that question?
Yeah, sure. Well, on the second piece of it, as Quentin said, we need to get our systems configured. We need to make sure the patient experience is correct. At this point, we have sent a couple hundred claims over to NGS. None of them have adjudicated yet. We do have a substantial patch of our clinical technician population that is located in that Midwestern and Chicago area. Once we know the claims are successfully adjudicating, then we will start to bring more of the clinical technicians that are already in that area and basically process the Medicare records that would've naturally flown through that area. Really, it's gonna be a second half impact. It's gonna be more minor.
I think the first half or first part of your question was more on the revenue. As Quentin said, you know, the updated guidance is a component of passing through the Q1 beat and then, you know, and then this NGS impact that we're gonna have in the second half of the year. You should look at this as we now think that the first quarter represents a higher fraction of the full year revenue than we were thinking of before. I think the thing we'd highlight is that, you know, January and February were noticeably slower because of Omicron.
We saw a stronger pickup in March, as Quentin had mentioned, than we were expecting at the time of the February call, which is what changed our view on what fraction of the year Q1 would be.
David, I would just.
Okay.
While we're talking about seasonality, you know, as we think about the second quarter, I just would keep in mind, you know, that the NGS benefit, to Doug's point, is likely to come in the back part of the year. I think sequentially you're gonna see a consistent step up in the business, that we've historically seen around that 8%-9% step up. That's sorta how we're thinking about, you know, Q1 into Q2, first half of the year and back half of the year.
Okay. Very helpful. Thanks again.
We have our next question from Bill Plovanic with Canaccord.
Great. Thanks. Good evening. Can you hear me okay?
We got you.
Excellent. So a couple of questions here. First, just wanted a little clarification, if we could just, I think I heard in the prepared remarks that revenue was up 13% sequentially, and unit volume was up 13% sequentially. Did I hear that correctly?
No, that's a little off, Bill. Revenue was up 13% sequentially. There's about a 10-point benefit in there from the Novitas increased rate effective January first. Volumes were up closer to that 3%-3.5% range sequentially.
Okay. Thanks for the clarification. Sorry, I just heard that wrong. Just wanted to clarify. Then, on XT mix, I think you, Douglas, your comments were that it's becoming a larger piece of the business. You know, I think it was running somewhere around 10%-ish as you exited the year. You know, has that become a bigger piece of the business? Is it like 11 or 12? Or as a percent of revenues, does it is it holding in?
Yeah. It certainly went up a couple of tenths. You know, it's comfortably above 10% for Q1.
Okay. If I can.
Continues to expand.
Okay. Just last question real quick is just on supply. You know, a lot of people, especially on the tech side, are having some challenges. Just wanted to ask, you know, in terms of inventory, circuit boards, all the electronic components you required, considering your high growth and you need a lot more and you're launching a new product, just any thoughts or commentary you could have on that. Thanks for taking my questions.
Yeah, Bill, I'll tell you, Douglas and team have done a terrific job of being out in front of that particular issue for the company, and this is something they started to tackle many, many months ago. We feel very good with respect to supply and access to the critical components, chips, for example, throughout the remainder of the year and being able to, you know, supply and support the guidance that we've put out there and continue to drive even beyond that and as hard as we can. I think the team's done a wonderful job here and I feel pretty good about where we're at. Douglas, I don't know if there's anything you'd like to add. Feel free.
No, I'd just reiterate what Quentin said. We're very comfortable in our position. I'd certainly say when you look at our balance sheet, you know, the other assets, which is where the printed circuit boards are covered, and then the inventory, you see that we are increasing those faster than we are increasing sales. It is very much that we are working to manage risk in this environment and, you know, bolstering up on, you know, the balance sheet assets here on, to make sure we're in a good position to be able to fully service our customers without concern.
Excellent. Thanks for taking my questions.
Thank you. We have our next question from Marie Thibault with BTIG.
Hi. Thank you. Good afternoon, and thanks for taking my questions. Congrats on a very nice quarter. Wanted to ask just one direct one here on the reimbursement. Is national CMS aware of the updated NGS rates? Have you had any conversations with them at a national level on that?
Yeah, Marie, I'm certain that they're aware of it. You know, one of the interesting things that we've sort of picked up on in the last probably four months or so, and we've spoken about this earlier, is that whereas historically, you know, we were never sure if CMS and the MAC were communicating together or not, it does seem like they have been communicating over the last several months here. What to read into that, we won't speculate, but we know that CMS is trying to get their arms around this and really learn as much as they can. They were actively interested in looking through the same sort of cost model that an independent third party pulled together from the industry and took all of the MAC through.
We're encouraged by all of those things. Obviously, we won't speculate on where it goes. We can't speculate. We'll wait and see what that proposed rule comes out at. It does seem like there is communication going on there, and I am certain they're aware of that NGS rate.
Okay. Very good. I'll ask my follow-up here sort of on the core business. We've certainly been hearing across the med tech landscape that labor shortages and staffing shortages within doctors' offices is maybe leading to less adoption of technology than ideal. Wondering if you've seen any of that to any extent. Clearly a very strong quarter, and I know you have in-home enrollments, but try to get a sense of where things are with the Zio XT on that.
Yeah. You know, we continue to hear that noise in the field for sure. You go out and you spend time with the physician. That's the number one issue that you hear them express concern around is just staffing challenges. I do believe that's been around for several months now, really back into the fourth quarter. I believe we're learning how to navigate through that environment. You know, we've reflected that in our guidance expectations. We do have the home enrollment model that I think we can continue to refine and get even better with and make it a real differentiating capability of the company. It is something that we can lean on.
Honestly, even back in the early part of, you know, January when Omicron sort of spiked a bit, we saw home enrollment spike a bit. I think there's an awareness to that opportunity out there in the marketplace, but we can drive it in a bigger way, which I think helps us navigate through some of the staffing challenges and the noise that we hear there. Yeah, it continues to be there. I do think we understand how to navigate through it at this point, and feel like we've captured that in our guidance pretty appropriately.
All right. Very good. Thank you for taking the questions.
Our next question is from Suraj Kalia with Oppenheimer & Co.
Good afternoon, everyone. Quentin, can you hear me all right?
I got you. Yep.
Perfect. Hey, first and foremost, congrats on a great quarter, Quentin. Let me start out broader picture, Quentin. Since the time you have joined iRhythm, Quentin, what are the average report delivery times, and what are the average technician reviews done per report now?
Yeah. You know, the average turnaround times are sitting around, you know, two to two and half days on average. Our stated objective is to turn those reports around in less than four business days. As you understand, the rest of the audience here probably understands, we ran into some challenges there back through the mid part of last year, but the team did a nice job of getting back ahead of that. Now we have the metrics in place that give us very clear visibility into how we're monitoring and managing that.
Not only do we monitor average turnaround times, but we pay very close attention to the number of reports that fall outside that four-day turnaround time, and it's minimal at this point, and it's been that way now for nearly five months, getting back into the fourth quarter. We feel great about the turnaround time issue and the ability to manage that, control that, and have the right number of resources here to be able to ensure that we continue to deliver a terrific experience for the patient. In terms of the number of technician reviews or oversight, you know, that's something that we can't really answer specifically because it depends on the sort of complications within the report that comes in.
We group our reports in different tiers, and depending on the tiers, might impact the amount of review that goes into that. Every tier is just a little bit different.
Fair enough. And Quentin, I'll just ask one more. I'll let others pick up the baton after this. Quentin, look, CMS has to know about Novitas and now NGS, right? It is almost inconceivable that they don't talk. At least that's what our field checks suggest. Please correct me if I'm wrong. NGS went from about, give or take, $200 to, let's say, $329, whatever it is. Novitas went from $115 to $233. If no new information was provided, I'd love to understand, you know, your expectations about national rates being higher. Would you still contend it should be higher than Novitas, or would you contend that it has to be higher than NGS now? Thank you for taking my questions, and congrats again.
Well, thanks, Suraj. Look, we continue to work with CMS, and we won't speculate on where they're gonna go. I will tell you there has been a lot of work done across the entire industry, not just iRhythm, but industry partners who have come together to articulate the cost, the investment that goes into delivering the sort of product service value that we're able to offer here. It's not just an independent unbiased perspective of iRhythm. We know in many cases, the data that got presented or has come together in that model was higher than iRhythm's submission. We know that we're not alone here in terms of the cost to provide this sort of service. What CMS does with that, you know, we're not gonna speculate on what that would be.
Is there an argument that the value could be above even where NGS is at? There is. We'll continue to work with CMS and respect their process, answer their questions, and we'll let them arrive, you know, at the position they're gonna arrive at. We continue to feel good about where this is at, and I think we understand very clearly the sort of value we can deliver, and it could support a higher rate.
Thank you.
We have no further questions in queue. I will now turn the call over to Quentin Blackford for closing remarks.
Well, thank you all for your time this evening. We appreciate the interest that you continue to demonstrate in iRhythm, and we're incredibly excited by the progress that we continue to make here at the company. I wanna take the opportunity just to thank all of our fellow employees here at iRhythm for all of the hard work and great work that's come together over the course of the first quarter. I think I share this across the entire company. We couldn't be more excited about the future that sits in front of this organization, not only in the core markets that we serve, where we know there's a significant runway of opportunity and a greenfield to continue to get after, but the adjacent markets have us excited as well.
Thanks so much and look forward to having a conversation the next time. Take care.
Thank you. Ladies and gentlemen, this concludes today's conference. We thank you for participating. You may now disconnect.