Although extending the duration of ambulatory electrocardiographic monitoring beyond 24 to 48 hours can improve the detection of arrhythmias, lead-based (Holter) monitors might be limited by patient compliance and other factors. We, therefore, evaluated compliance, analyzable signal time, interval to arrhythmia detection, and diagnostic yield of the Zio Patch, a novel leadless, electrocardiographic monitoring device in 26,751 consecutive patients. The mean wear time was 7.6 ± 3.6 days, and the median analyzable time was 99% of the total wear time. Among the patients with detected arrhythmias (60.3% of all patients), 29.9% had their first arrhythmia and 51.1% had their first symptom-triggered arrhythmia occur after the initial 48-hour period. Compared with the first 48 hours of monitoring, the overall diagnostic yield was greater when data from the entire Zio Patch wear duration were included for any arrhythmia (62.2% vs 43.9%, p <0.0001) and for any symptomatic arrhythmia (9.7% vs 4.4%, p <0.0001). For paroxysmal atrial fibrillation (AF), the mean interval to the first detection of AF was inversely proportional to the total AF burden, with an increasing proportion occurring after 48 hours (11.2%, 10.5%, 20.8%, and 38.0% for an AF burden of 51% to 75%, 26% to 50%, 1% to 25%, and <1%, respectively). In conclusion, extended monitoring with the Zio Patch for ≤14 days is feasible, with high patient compliance, a high analyzable signal time, and an incremental diagnostic yield beyond 48 hours for all arrhythmia types. These findings could have significant implications for device selection, monitoring duration, and care pathways for arrhythmia evaluation and AF surveillance.
Ambulatory electrocardiography is a widely used diagnostic tool to detect arrhythmias for a variety of symptoms and conditions. Because of memory and technical limitations, ambulatory electrocardiographic (ECG) monitors have historically provided either short-term (24 to 48 hour) continuous monitoring (Holter) or longer term intermittent (triggered) monitoring (event or loop recorder). Continuous ECG monitoring longer than the traditional 24- to 48-hour duration might improve the diagnostic yield of infrequent arrhythmias. However, such technologies have generally been limited by patient compliance, the analyzable wear time, and electrode skin irritation. We, therefore, investigated the patient compliance, device analyzable time, and diagnostic yield of a novel, leadless, wearable monitor for extended ambulatory ECG monitoring.
Methods
We performed a cross-sectional study of patients receiving a single-use, long-term, continuous, cardiac monitoring patch for clinical indications. The Zio Patch monitor (iRhythm Technologies, San Francisco, California) is a compact (123 × 53 × 10.7 mm), lightweight (34 g), and water-resistant, cutaneous single-lead ECG monitor that provides ≤14 days of continuous ECG data obtained from a single vector. The single-use device is placed over the patient’s left pectoral region with skin adhesive and is typically applied by trained technicians at the ordering ambulatory clinic. A button can be pressed by the patient to annotate symptoms ( Figure 1 ). After completion of the monitoring period, the patient mails the device and diary to the data processing center, where the data are analyzed, and a report is generated and sent to the ordering physician.
We obtained de-identified data from the device manufacturer and servicer (iRhythm Technologies) for all patients who had completed Zio Patch monitoring for clinical indications from January 1, 2011 to December 31, 2011. These data were transferred to us after removal of all patient-, physician-, and site-level identifiers. We included all Zio Patch data from consecutive patients receiving first-time patches at the enrolling site. We excluded data for repeated or subsequent Zio Patch monitoring to minimize confounding by indication. A local institutional review board and the Veterans Affairs Palo Alto Health Care System research and development committee approved the present study.
The clinical indication for monitoring was ascertained from a free-text variable that was entered by the ordering provider. Trained research staff aggregated the indications into 11 categories: palpitations, AF, syncope or presyncope, bradycardia, supraventricular tachycardia (SVT), unspecified tachycardia, ventricular tachycardia (VT), pause, second degree Mobitz II or third degree (complete) atrioventricular block, polymorphic VT (including torsade de pointes and ventricular fibrillation), and other indications. If a patient had >1 clinical indication, all indications were retained for analysis.
Arrhythmia adjudication was performed and coded using a 2-step process. First, the servicer applied a digital signal processing algorithm to continuously recorded ECG data to identify potential arrhythmia episodes. The algorithm, cleared using the 510(k) method by the Food and Drug Administration for clinical use, detects potential arrhythmias by detection of the heart rate, irregularity, and morphology. The algorithm then uses the heart rate increase from the preceding portion of heart rate regularity (sinus rhythm) to confirm a candidate episode. Next, trained and certified cardiovascular technicians employed by the servicer re-examined the detected arrhythmia episodes to confirm the diagnoses and to classify the arrhythmia where appropriate. Because the algorithm assigns an arrhythmia classification to every portion of the continuous recording, a second detected rhythm (including artifact) occurring in the middle of an arrhythmia event can cause the event to be classified as multiple discrete episodes. These episodes are reclassified on review by technicians to a single arrhythmia event, when appropriate. Arrhythmia adjudication was performed for clinical findings by technicians with no knowledge of the present study.
The episodes were classified into 3 categories according to the type of arrhythmia: first occurrence, first symptomatic occurrence (if occurring 45 seconds before or after patient triggering), and longest duration. The arrhythmias were classified into the following independent, but not mutually exclusive, categories: atrial fibrillation (AF), pause >3 seconds, second-degree Mobitz II or complete atrioventricular block, SVT, VT, and symptomatic bradycardia. The AF burden was further calculated as the percentage of analyzable time. We segmented the AF burden into the following categories of paroxysmal AF (<1%, 1% to 25%, 26% to 50%, 51% to 75%, and 76% to 99%) and chronic AF (100%). For analytical purposes, we did not count chronic AF as an arrhythmia event or toward the diagnostic yield. This method has been shown to have excellent agreement with simultaneously acquired Holter recordings for the detection of AF (κ = 1.0) and quantification of AF burden (r = 0.96).
The total wear time was calculated from the point of activation to the point of the last recorded analyzable signal. Wear time end points of 2, ≥6, and ≥13 days were used to mark the comparison points of the typical 48 hours (Holter), 1 week, and 2 weeks of ECG monitoring. The device analyzable time fraction was defined as the proportion of the total wear time that the ECG signal is interpretable (sufficiently free of noise) by the arrhythmia detection algorithm.
Descriptive statistics were performed using STATA, version 11 (StataCorp, College Station, Texas) for analysis. Continuous variables and proportions were compared using the t test and chi-square test, respectively, and p <0.05 was considered significant. All analyses were performed by 2 of us (D.D.H., M.P.T.) and were independently verified and reproduced by a second statistician (X.X.).
Results
Of the 28,038 consecutive Zio Patch studies from January 2011 to December 2011, we included 26,751 first-time studies (95.4%) of unique patients and excluded 1,287 repeat studies from the present analysis.
The mean age was 60.2 ± 18.7 years, and 54.5% of the patients were women. The mean wear time was 7.6 ± 3.6 days. The median wear time was 7.0 days (25th to 75th percentile interquartile range 5.9 to 9.3); 95.9% wore the device >48 hours, 74.3% wore the device ≥6 days, and 16.1% wore the device ≥13 days. The median analyzable time, expressed as a percentage of the total wear time, was 99% (interquartile range 94% to 99%); 87.1% of the patients had an analyzable time the equivalent of ≥22 hr/day. No significant difference was found in age or wear time between the genders.
The provider-reported clinical indications are listed in Table 1 ; the most prevalent indications were palpitations, atrial fibrillation, and syncope or presyncope.
| Variable | Patients (n) |
|---|---|
| Palpitations | 10,786 (40.3) |
| AF | 6,493 (24.3) |
| Syncope or presyncope | 4,029 (15.1) |
| Bradycardia | 964 (3.6) |
| SVT | 570 (2.1) |
| Unspecified tachycardia | 547 (2.1) |
| VT | 187 (0.7) |
| Pause | 48 (0.2) |
| AV block ∗ | 44 (0.2) |
| Polymorphic VT, torsade de pointes, VF | 6 (0.0) |
| Other indications † | 3,557 (13.4) |
∗ Second-degree Mobitz II or third-degree AV block.
† Providers reported unspecified arrhythmias, nonarrhythmic cardiovascular indications, or no indication, exclusive of indications listed.
The overall prevalence of single and multiple arrhythmias is listed in Table 2 . Arrhythmias, not counting chronic AF, were detected in 16,142 patients (60.3%). Of all the patients, 12,298 (46.0%) had a single arrhythmia and 3,083 (11.5%) had multiple arrhythmias (not including chronic AF). Chronic AF was present in 2,003 patients (7.5%), and 761 of these patients (2.8%) had other arrhythmias, in addition to chronic AF.
| Variable | Patients (n) | All Patients With Arrhythmia (%) | Women (%) |
|---|---|---|---|
| Detected arrhythmias (excluding chronic AF) | 16,142 (60.3) | 100.0 | 52.0 |
| Single arrhythmias (excluding chronic AF) | 12,298 (46.0) | 76.2 | 56.5 |
| Multiple arrhythmias (excluding chronic AF) | 3,083 (11.5) | 19.1 | 39.7 |
| Chronic AF | 2,003 (7.5) | — | 39.4 |
| No other arrhythmias | 1,242 (4.6) | — | 45.2 |
| ≥1 Other arrhythmias | 761 (2.8) | 4.7 | 30.0 |
| No arrhythmia | 10,609 (39.7) | — | 58.3 |
The distribution and time to the detection of each category of asymptomatic arrhythmias are listed in Table 3 . Overall, the mean and median time to the first arrhythmia was 1.7 ± 2.2 days and 0.8 day (interquartile range 0.2 to 2.4), and the mean and median time to the first symptom-triggered arrhythmia was 3.0 ± 2.9 days and 2.1 days (interquartile range 0.8 to 4.4), respectively. Among the patients with arrhythmias, the most common was SVT.
| Variable | All Patients (%) | All Patients With Arrhythmia (%) | Women (%) | Time to First Arrhythmia | Time to First Symptomatic Arrhythmia | ||||
|---|---|---|---|---|---|---|---|---|---|
| Mean ± SD (days) | Median (IQR) | Occurring After 48 hrs (%) | Mean ± SD (days) | Median (IQR) | Occurring After 48 hrs (%) | ||||
| Any arrhythmia | 60.3 | 100.0 | 52.0 | 1.7 ± 2.2 | 0.8 (0.2–2.4) | 29.9 | 3.0 ± 2.9 | 2.1 (0.8–4.4) | 51.1 |
| Atrial fibrillation burden (%) | 17.3 | 28.7 | 41.0 | 1.4 ± 2.1 | 0.4 (0.1–1.8) | 23.4 | 2.7 ± 2.8 | 1.8 (0.6–4.0) | 47.2 |
| <1 | 2.9 | 4.8 | 46.2 | 2.2 ± 2.7 | 1.2 (0.3–3.3) | 38.0 | 3.8 ± 3.6 | 2.7 (0.9–5.7) | 57.4 |
| 1–25 | 4.8 | 7.9 | 41.1 | 1.2 ± 1.8 | 0.4 (0.1–1.5) | 20.8 | 3.2 ± 2.9 | 2.3 (0.9–4.7) | 56.5 |
| 26–50 | 1.3 | 2.1 | 40.4 | 0.7 ± 1.3 | 0.1 (0–0.6) | 10.5 | 2.6 ± 2.8 | 1.5 (0.4–3.9) | 40.4 |
| 51–75 | 0.6 | 1.0 | 35.4 | 0.6 ± 1.2 | <0.1 (0–0.6) | 11.2 | 2.2 ± 2.2 | 1.6 (0.6–3.3) | 39.3 |
| 76–99 | 0.3 | 0.4 | 43.0 | 0.2 ± 0.4 | <0.1 (0–0.3) | 1.4 | 1.8 ± 2.9 | 0.7 (0.2–1.7) | 23.1 |
| 100 (chronic AF) | 7.5 | — | 39.4 | — | — | — | — | — | — |
| Pause >3 s | 3.7 | 6.1 | 38.9 | 2.8 ± 2.9 | 1.7 (0.6–4.0) | 46.6 | 3.0 ± 3.1 | 1.8 (0.8–5.1) | 42.9 |
| Mobitz II or complete AV block | 1.4 | 2.3 | 37.3 | 2.2 ± 2.9 | 1.0 (0.3–2.7) | 34.1 | 2.3 ± 2.8 | 1.0 (0.6–3.1) | 36.6 |
| SVT (beats) | |||||||||
| ≥4 | 45.9 | 76.1 | 56.1 | 1.9 ± 2.3 | 1.0 (0.3–2.6) | 32.3 | 3.4 ± 3.0 | 2.5 (1.1–5.1) | 59.1 |
| ≥8 | 30.8 | 51.1 | 57.1 | 1.4 ± 1.9 | 0.6 (0.2–1.8) | 23.3 | 3.3 ± 2.9 | 2.3 (1.0–4.9) | 58.0 |
| VT (beats) | |||||||||
| ≥4 | 12.3 | 20.4 | 36.1 | 3.4 ± 3.2 | 2.6 (0.9–5.2) | 58.3 | 3.7 ± 3.1 | 3.0 (1.1–5.6) | 63.3 |
| ≥8 | 4.7 | 7.8 | 34.7 | 3.0 ± 3.0 | 2.1 (0.5–4.6) | 51.2 | 3.6 ± 3.2 | 2.7 (1.0–5.6) | 61.0 |
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