Still waiting for the clock to tick, too. All right, we're good. Perfect. Good afternoon, everyone. Thanks for joining us at the William Blair Growth Stock Conference. My name is Margaret Kaczor Andrew. I am the MedTech analyst here at William Blair that covers iRhythm. For a complete list of research disclosures and conflicts of interest, please go to williamblair.com. Now, before we kick off the presentation, apologies for those that don't want to hear from me, but you're going to hear from me anyways. You know, just a brief comment on iRhythm. We named iRhythm as the Topic of the Year. While it's done really, really well for us, there's a lot of strong reasons for continued fundamental momentum in not only their core markets, but we view it as one of the strongest names in our universe that can benefit from the next evolution of health care.
That's really personalized medicine. Everyone talks about AI changing the landscape of, frankly, the world. Some people are believers, some people, frankly, aren't believers, and that's OK. iRhythm is actually one of those companies that has already figured out a way to monetize and create a tremendous amount of value with AI. As we look at the next vector of growth with AI, I would actually take it to the next level, and that's personalized medicine and asymptomatic care. That's the way to be able to tailor treatment and disease prevention, excuse me, to patients. In our view, this is not a maybe. This is not, you know, that it's not happening. It's actually actively happening.
These guys are seeing it in their volumes and, what I would argue, meaningful volumes, just in a matter of four to six quarters, probably, with value-based care contracts and asymptomatic growth. Watch this space, watch this name. With that, I'm going to turn it over to Dane.
Appreciate it, Margaret. No pressure with that kind of introduction. Good to be here with you all. Appreciate you all taking an interest in iRhythm. This is a growth conference. We do believe iRhythm is a growth story. I do believe this is a good fit for us. I'm going to add three adjectives to the word growth to start, which is durable growth, profitable growth, and scaled growth. I hope those elements come through in the presentation today. Before I jump in, a quick note. I will be making forward-looking statements here. Please refer to our quarterly and annual filings for more information on risk factors and other important information for you. iRhythm is a digital health care company. We started or commercially launched a little more than a decade ago, have really changed the standard of care in cardiac monitoring.
Not done there, which we'll talk about where we're going from here. Changing that standard of care away from traditional short-term Holter monitors has been our effort over the last decade or so. That has been enabled by a technology platform that is highly scalable, proprietary to iRhythm, that combines really the power of wearable biosensors, sophisticated AI tools, and then a digital platform on the back end to deliver it all seamlessly to clinicians. Prior to our introduction, the standard of care for patients in cardiac monitoring were short-term Holter monitors. This is capital equipment, wires everywhere, very inconvenient for a patient to wear these monitors. Most importantly, only monitoring patients for up to 48 hours. Cardiac arrhythmias are intermittent by nature.
When you're monitoring for a short period of time, you're going to miss important arrhythmias or not find the most critical arrhythmia that's present there in the patient. Monitoring out to 14 days, which is enabled by the wearable biosensor that we've developed here, picture there of Zio monitor, our latest generation hardware, allows a patient to wear this comfortably for up to 14 days. They can go about their normal day-to-day activities, shower, sleep, exercise, and really let this kind of fade into the background of their lives. Over those 14 days, we're collecting, on average, one and a half million heartbeats. A lot of data coming off of the patient. It really does require very powerful, sophisticated AI tools to draw out the most important insights of the data coming from the patient. We've invested from the very beginning on the AI in the back end.
It's embedded in our product. It's core to everything that we do and is critical for the future success of the company as well. I mentioned the digital platform. Don't underestimate that part of it. It is critical to be easy to do business with. We have to provide those insights really at the point of care for clinicians, make it easy for them to access the most critical aspects of the patient data. We make that easy for clinicians right at the point of care. A few numbers here that I think highlight iRhythm in terms of where we are in our journey. Starting with revenue from our most recent reported quarter, $158.7 million in revenue in our first quarter of 2025. That was an increase of over 20% year- over- year compared to the first quarter of 2024.
That was the second consecutive quarter of annual growth over 20%, which speaks to the growing momentum that we're seeing in the business. In fact, we saw growth kind of accelerate as we moved through 2024, eclipsing that 20% number in Q4 last year and Q1 this year. I mentioned scale early on. We are now serving over 2 million patients a year and able to do that efficiently. Our core market, we characterize that today as 6.5 million tests. That over 2 million patients we're serving represents approximately 30% of our core market today. That is not how we believe or how we view our market longer term. It is more in line with this 27 million patients. I am going to dig into that. That is a number you are going to hear quite a bit as I go through the presentation. Another big opportunity for us is international.
There's 5 million tests outside the U.S., ambulatory cardiac monitoring tests. We have the same opportunity outside the U.S. in terms of changing the standard of care. That's something that we're getting after. In terms of the evidence that has been critical to our success as well, we have over 125 clinical papers demonstrating the clinical superiority of our technology, of Zio. That's been fundamental to changing the standard of care in the U.S. Then 2.5 billion hours of curated ECG data. From the very beginning of the company, we have been collecting every one of those heartbeats that we've monitored. That has driven this 2.5 billion hours of data. That is critically important to train and develop the AI tools that are critical to our business.
As you think about the problem that we're trying to solve, the burden of cardiac arrhythmias in the U.S. is immense, both from a clinical standpoint as well as a financial standpoint. Over 11 million patients with arrhythmias. You have a 40% lifetime risk of developing atrial fibrillation, the most common cardiac arrhythmia once you're over the age of 55. A highly prevalent disease. The consequences are quite severe. Five times increased risk of stroke for patients that have atrial fibrillation and over 160,000 deaths per year associated with atrial fibrillation. Financial burden is just as problematic. Obviously, the clinical impact is quite devastating. Margaret alluded to this.
If you think about where the health care market is moving or should be moving to more preventative, proactive care, we are perfectly positioned to enable that shift and make a positive impact on millions of patients' lives and have an impact on these numbers. Again, if you think about our core market today, 6.5 million ACM tests being done every year in the U.S. That's segmented further. There's long-term continuous monitoring, which is where we operate with our Zio monitor device. We have over 70% market share in that category. That is a category, a segment that we pioneered. This did not exist before we came to market over a decade ago. There continues to be an opportunity to shift away from short-term traditional Holter monitors that I mentioned earlier.
Despite all of our success, there's still 1.5 million short-term Holter tests being done every year in the U.S. That continues to decrease every year and benefit or shift to long-term continuous monitoring, where we have over 70% share with Zio Monitor. The other opportunity for us within the core market of 6.5 million tests is the mobile cardiac telemetry segment with our Zio AT products. We have just over 10% market share there. Have been growing that share nicely since we introduced Zio AT back in 2019. Have seen really good momentum with AT recently in the last two quarters, which has contributed to that growth that I mentioned. A meaningful opportunity to grow our share of the MCT segment more in line with that 70% share that we have on the long-term continuous monitoring side.
Importantly, often high overlap and correlation in terms of the prescriber base for both long-term continuous and MCT. We have a real opportunity to grow our share in that MCT segment. In terms of TAM expansion opportunity, two that I'd point to, again, international, 5 million tests outside the U.S. I'll talk about the countries that we're prioritizing and have entered into recently. That is a meaningful opportunity for us. Within the U.S., again, 27 million patients that we believe are candidates for cardiac monitoring with Zio. These are patients that are showing up in primary care today with cardiac palpitations noted in their medical records, yet only 6.5 million tests are being done. A real opportunity as we move into primary care to capture those 27 million patients. Starting with international.
International really has not been a contributor to growth for the company historically. Over 98% of our revenue is from within the U.S. We have a small business outside the U.S. in the U.K. We have seen volumes grow there nicely. We are trying to secure NHS-wide reimbursement. That is an effort that has been ongoing for several years now and hopefully break through there in terms of getting NHS-wide reimbursement. We have a nice business today in the private sector within the U.K., but ultimately want to be able to serve that entire market. Late last year, we entered into four Western European countries: Switzerland, Spain, Austria, and the Netherlands. That was stood up in late 2024, so really just getting started. France and Germany are also on the list longer term. Those are big market opportunities.
Take a little longer to turn on for us, but those are on the roadmap as well. Japan, second biggest market outside the U.S., 1.6 million ACM tests done per year there. Received regulatory approval in Japan late last year and a reimbursement decision just a couple of months ago. We have now launched in Japan. Initially, we will be operating under the local Holter rate in Japan, which was a somewhat disappointing outcome for us, to be honest. We do believe we are bringing more value to the patients there than traditional Holter monitors. The feedback was very clear. We need to generate in-market evidence of Zio relative to Holter monitors on the market in Japan. That will be our effort over the next year or two to develop that evidence, get back in the reimbursement process, and ultimately secure higher reimbursement. Now back to the U.S.
I've mentioned this 27 million number a couple of times now. Breaking that down, over 15 million patients are showing up today in primary care, again, with symptoms suggestive of an underlying arrhythmia. Yet only 6.5 million tests are being done per year. A real opportunity as we're pushing upstream into primary care to capture those 15 million patients. Those are all candidates for Zio and really should be monitored with Zio. In addition to that, another 16 million that have risk factors suggestive of an underlying arrhythmia. These patients may not necessarily be showing up in primary care with symptoms. Could be masked by other diseases, whether it be diabetes, hypertension, and another disease that essentially masks the symptoms of the arrhythmias.
We've been generating a lot of clinical evidence that I'll hit here in a minute that show there are significant undiagnosed arrhythmias in these populations. Again, our view is these patients should be proactively monitored. I mentioned before, easy to do business with. It's critical for us to make Zio easy to get on patients, easy for clinicians to adopt into their workflows to make this 27 million patient opportunity a reality for us. We're approaching this in kind of a two-pronged strategy. First, we have a land and expand strategy. This has always been kind of fundamental to our business, where we open an account typically through cardiology or electrophysiology as the clinical champion. They introduce Zio into the account. We quickly look to expand into other departments across that account. Primary care is one opportunity for expansion. Neurology, nephrology, emergency room, or other opportunities.
We try to get after all of those. That is one strategy. That has been really at work for several years now. We have organized our sales team, organized our commercial strategies to really drive this land and expand model. The second approach here is the top-down focus on this, what we call innovative channel. There are some logos noted on the page here. These are value-based entities, primary care entities that own the risk of the patient. These are often big accounts that have a nationwide presence and a very powerful kind of one-to-many selling model here. Early in the effort here, but seeing really good signs that this is opening up in a meaningful way for us. There is a data point on the slide here. Across these five accounts represented on the page here, over 30,000 patients monitored.
80% of those patients, and these were both symptomatic and asymptomatic patients, but over 80% came back with an arrhythmia diagnosed in the report. It is clear that there are undiagnosed arrhythmias out in these patient populations. There is real benefit in proactively monitoring these groups. Primary care, again, has been an effort we've been getting after for several years. We mentioned on our Q1 call, over 30% of our volume is now being prescribed out of the primary care channel. Really making good progress there. That is not the stopping point, right? We will continue to see a meaningful shift upstream into primary care. As it relates to the innovative channel, this second channel here, that's a subset of over 30%. Think of that as kind of low single digits in terms of current volume.
That was essentially zero two years ago, if not 18 months ago. This is a new emerging segment for us, very encouraging. This is our opportunity to get to that 27 million patient population that I mentioned. Related to that, Margaret mentioned, I think you said personal medicine or targeted medicine. We are absolutely approaching that with that mindset. We are developing algorithms that will essentially work with our innovative channel partners to say, "Target this patient population, and you will get an 80% diagnostic yield." We can broaden that and take it down to 40%. We can tighten it and take it to 90%. Really kind of dialing in that fidelity of monitoring these patient populations and finding those undiagnosed arrhythmias in the patient population, ultimately to prevent downstream health care costs, right?
The pitch to these entities are these patients will get diagnosed sometime and somewhere. You kind of have the choice. You can proactively monitor these patients, diagnose them at home with Zio, low cost. Or you can leave these patients to be, and they're going to show up in the emergency room with a clinical event. That will cost you thousands of dollars. Again, the ROI is very clear here. We believe we're just getting started and really excited about the opportunity. In terms of our kind of competitive advantage to essentially secure the opportunities that I just laid out, I would say it's multifaceted. AI, again, is a big component of our business. It's been a critical enabler. You really cannot deliver the scale and the volumes that we deliver without utilizing AI tools.
That is, together with the IDTF, the clinical operations backend, allows us to serve, again, over 2 million patients and really scale with our accounts. We have a first-mover advantage. I mentioned we were the pioneer in this segment. We have a great brand reputation in the market. We are the market leader. There is high confidence and physician agreement with the clinical report that we're delivering, over 99% agreement with the clinical report that we deliver at the end of the wear. Clear provider preference there. I mentioned workflow a few times now. That is critically important. EHR integration is something that we have been pursuing for several years. Over 40% of our volume is now through EHR integrations. We have an Epic partnership that I'll mention here in a minute. That is, again, as important as being clinically superior.
You got to be easy to do business with, particularly as you're looking to move upstream into primary care and capture those 27 million patients. I mentioned our collaboration with Epic Aura. So this is something we announced about a year ago. Really excited about this. I mentioned EHR integrations across all EHR providers, not just Epic. Now represents about over 40% of our volume today. The benefits are twofold. One, again, we're embedding Zio within the clinical workflows of our clinicians, of our physicians, making it easier to prescribe Zio and ultimately to read the report at the end of the service. Epic Aura kind of takes that even further and really lowers the amount of resources required to get to EHR integration today. With a traditional integration, it can sometimes be a six-month effort with an account, a heavy burden on their IT resources. Epic Aura significantly reduces that.
This is something that we announced over a year ago. We now have a little bit less than 10 customers integrated from an Epic standpoint, seeing really good early results there. Small numbers, again, less than 10 accounts, but on average, kind of a 20% uptick in volume pre and post integration. It makes our business very sticky once an account kind of invests with us into EHR integration. This is something we're going to continue to lean into. In terms of where we go from here, today our Zio monitor really just collects ECG data. We see a real opportunity to start developing additional vital signs onto our platform. We announced a technology licensing agreement with BioIntelliSense about a year ago, a little more than a year ago, to start to bring other parameters onto our monitor. PPG-based vital signs, accelerometry-derived vital signs.
That can be respiration rate, heart rate variability, SpO2. A lot of opportunity that this affords us. One, it will deepen our competitive moat within our existing business, within our core business. The more insight, the more clinical value we can deliver, the more we'll remain the provider-preferred device. It starts to open up other opportunities for us, right? The more information you're gathering from patients, the more insights you can ultimately deliver. This will open up opportunities in sleep, hypertension, heart failure. This is something we're really excited about. Near term, Zio MCT is our next-generation device. That remains our focus and our priority. Next generation after that, we'll start to incorporate these multivital signs. We're excited about what that can do for us. Of course, all of that data only matters if you can make sense of it.
Again, this is where the AI capabilities are core to everything that we do. We will continue to invest in the AI part of our business. We have a second-generation deep-learned FDA-cleared algorithm. We are working on our third and real opportunity to continue to draw out more and more clinical insights for the patients that we serve today. Maybe a quick comment here. iRhythm has been on a journey to kind of professionalize and mature the company over the last several years. We had a new CEO join us, Quentin Blackford, about four years ago. He has revamped our leadership team and has really a leadership team that is ready and capable to go execute on everything that you just heard. Excited about what we're doing there. We're also building out the operational infrastructure of the company.
This has been an important part of everything that we do to make sure that we're enabling ourselves to get after those opportunities that I went through. I think most of you are familiar. We're working through FDA warning letter. That is our number one corporate priority in terms of remediation. Making very good progress there, excuse me. From a warning letter standpoint, we've completed 100% of the activities related to warning letter remediation, 80% complete on the 483 observations that we received in August last year, 80% complete, hitting every timeline and commitment that we laid out to the FDA at that time and look to be wrapping those activities up in the midpoint of this year. One other update, I know investors sometimes ask about the DOJ subpoena. We received that two years ago. We have been complying with that, providing documents to the DOJ.
There was a motion to compel for three documents, a handful of documents, summer of last year, asking us to waive attorney-client privilege. We did hear from a judge recently that they ruled in favor of the DOJ, asking us to turn over those documents. That is a recent update. I know that is a question we get from investors. I wanted to provide that update. I do not believe it materially changes anything in terms of potential outcomes here. It is a question we get. In full transparency, I wanted to provide that update. As I wrap here, maybe quickly back on the financial performance of the company. Again, $158.7 million of revenue in the first quarter, second consecutive quarter of over 20% growth. Again, seeing really nice building momentum in the company and excited about the setup for the year.
On a profitability standpoint, a big mention of the start, profitable growth. That has been a bigger and bigger focus for the company to make sure we continue to grow the company, but continue to do it in a profitable way. We want to see that profitability margin expand consistent with the top line as well. Gross margin saw 68.8%, 250 basis point improvement year- over- year relative to the first quarter of 2024. Negative 1.7% adjusted EBITDA margin, a 750 basis point improvement relative to Q1 2024. Seeing really good leverage in the business. We will continue to see really good leverage in the business. Importantly, the opportunity is really in the G&A part of our business.
If you were to break that leverage down, really getting after the G&A portion, continuing to invest in R&D and sales and marketing to really drive near and long-term growth for the company. From a guidance standpoint, we did take the opportunity to update guidance following our Q1 call early in the year. We were seeing very positive signs in the business and had confidence to raise revenue and profitability guidance despite being just a quarter into the year. New guidance for the year, $690 million-$700 million of revenue, 7.5%-8.5% adjusted EBITDA. Maybe just a couple of comments in terms of how we approach guidance. We want to be thoughtful with guidance. We want to bake in essentially what we have high confidence in and really hold back things that are maybe emerging in the business, right?
We've talked about innovative channel as a kind of early opportunity for us, seeing really good indicators that that is opening up for us in a meaningful way, has contributed to some of the performance more recently in the last two quarters. It's still early enough, though, where our predictability, our visibility into that segment is not high enough where we have confidence to really bake that in in a meaningful way in guidance. That's something we will leave outside of guidance. I will wrap here just with a synopsis of kind of how we view our opportunity to create long-term shareholder value creation, right? We have a clear set of opportunities. Hopefully, that was clear in the talk today. We're investing in both innovation from an R&D standpoint, from a technology standpoint, but also that operational infrastructure to support that growth.
We want to do that profitably. That is a big focus for us. We want to be good stewards of the business and really bring some fiscal discipline into the company. With that, I will wrap there. Really appreciate everyone's time today. Our breakout room is.
the Adler room.
Adler room. Thank you so much.
Thank you.
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