This study is a nonrandomized, single-center, prospective cohort study. We evaluated patients who had been admitted to our hospital for myocardial infarction and discharged after treatment. Eligible patients had a history of acute myocardial infarction and provided written informed consent to participate. Exclusion criteria were as follows: (1) previously diagnosed with atrial fibrillation, (2) implanted pacemaker, cardioverter-defibrillator, or any electrical devices, and (3) skin problems such as allergic contact dermatitis. Our prospective study enrolled 73 adults aged 55 years or older from April 2020 to November 2020. Among them, 2 participants dropped out due to loss of the device before data acquisition.

ATP-C120 is a single-lead ECG monitoring device that can continuously monitor the ECG signals for as long as 14 days (11 days if the device is connected to a smartphone via Bluetooth) when attached to the skin over the area of the heart (Figure 1). The device weighs about 13 g, with dimensions of 95.0 × 50.6 × 8.3 mm. This is the smallest of the contemporary wearable patch devices worldwide.

When the device is attached to the patient, several predefined methods are used to prevent the occurrence of noise or signal loss. First, the skin is cleansed and disinfected using a 70% ethanol solution. Skin hair is removed if necessary. Subsequently, the protective film is removed from the patient-side surface of the device. The device is placed at the left third intercostal space, tilted inward 45 degrees. A continuous ECG signal is recorded to a memory card for 11 days. Subsequently, the device is linked to a computer and the data are downloaded and analyzed by a specific program (AT-report) provided by ATsens.

According to institutional Good Clinical Practice for medical devices, we attached the experimental ATP-C120 device to participating patients. We obtained demographic data, as well as past and present medical and drug administration history, and conducted physical examinations (height, body weight, and vital signs such as systolic and diastolic blood pressure and pulse). In addition, laboratory parameters (complete blood count, electrolyte, blood urea nitrogen, creatinine, estimated glomerular filtration rate, liver function tests, lipid panel, fasting blood sugar, and glycated hemoglobin A_1c or HbA_1c) and the 12-lead ECG results before the attachment of the ATP-C120 device were obtained. We detached the device after 11 (SD 5) days and recorded the date and time. Two independent cardiologists analyzed the recorded data for arrhythmic detection.

We hypothesized that ATP-C120 could detect 10% of new-onset atrial fibrillation in patients with postmyocardial infarction. We set the type I error as .05 and confidence limit as 5%. Application of these parameters resulted in 139 participants. The attrition rate was set as 5% and, thus, the final sample size was 146 participants. However, we only enrolled 73 patients because of limited enrollment time and funding, which was adjusted by the project manager of the Korean Health Industry Development Institute.

Data are presented as numbers and frequencies for categorical variables and as mean (SD) for continuous variables. The incidence of atrial fibrillation followed by myocardial infarction is described as proportions and 95% CIs. A 2-sided P value of <.05 was indicative of a statistically significant difference. To evaluate interobserver reliability and interdevice reliability, Cohen κ coefficient was calculated. For comparisons between patients with or without atrial tachycardia, chi-square test (or Fisher exact test when any expected count was <5 for a 2 × 2 table) was performed for categorical variables. Statistical analyses were performed using R (version 3.1.0; The R Foundation for Statistical Computing).

The study was reviewed and approved by the Institutional Review Board of Seoul National University Bundang Hospital (B-2003/603-002).

A total of 71 patients who had a history of acute myocardial infarction were included in the analyses. The baseline characteristics are shown in Table 1. The mean age was 67.6 (SD 8.3) years, and 59 (83%) patients were men. Among the study population, 23 (32%) patients were clinically diagnosed with ST-segment elevation myocardial infarction, and 40 (56%) participants were attached with the ATP-C120 device within 6 months of acute myocardial infarction. Patients with previous heart failure were not enrolled in this study. The average left ventricular ejection fraction (LVEF) was 57.1% (SD 8.2%), and pro–B-type natriuretic peptide level was 370.3 (SD 505.3) pg/L. For medication, 61 (86%) participants received aspirin, whereas 37 (52%) participants received P2Y12 inhibitor. In addition, among the study population, 56 (79%) patients received β-blockers, 23 (32%) patients received renin-angiotensin system inhibitors, and 18 (25%) patients received calcium channel blockers.

The incidence of arrhythmias as detected by ATP-C120 and confirmed by 2 cardiologists (C1 and C2) is shown in Table 2. One participant was concordantly diagnosed with atrial fibrillation by both cardiologists (Figure 2A). The cardiologists determined that atrial premature beats occurred in 65 (92%) (C1) and 60 (85%) patients (C2), and ventricular premature beats occurred in 38 (54%) (C1) and 44 (62%) patients (C2). No ventricular fibrillation was recorded and only 1 nonsustained ventricular tachycardia event was noted by both cardiologists (Figure 2B). Remarkably, 40 (56%) patients (according to both C1 and C2) showed paroxysmal atrial tachycardia, which was sustained less than 2 minutes (Figure 2C).

In Table 3, additional analyses of patients with atrial tachycardia are shown.

In general, there were no significantly different characteristics between patients with atrial tachycardia and those without atrial tachycardia. The timing of monitoring after acute myocardial infarction was not significantly different (55% vs 45%; P=.56). The LVEF (mean 56.1%, SD 8.6% vs mean 57.9%, SD 7.8%; P=.35) and the size of left atrium or left atrial volume index (mean 32.3, SD 8.9 vs mean 35.6, SD 12.9; P=.31) were not significant contributors to atrial tachycardia. However, among medications, the use of β-blockers made a significant difference (70% vs 90%; P=.04) (Table 3). Furthermore, when we analyzed participants based on different β-blocker dosages, there were no significant differences (Table 4).

Lastly, reported adverse events associated with the ATP-C120 patch are described in Table 5. Among the participants, 21 (30%) complained of itching during the patch monitoring period, 2 (3%) experienced abrasion (Figure 3A), 1 experienced bullae (Figure 3B), and 1 showed erosion but fully recovered without scarring or altered pigmentation (Figure 3C).

In this study, we analyzed 71 patients’ ECG signals after myocardial infarction for 11 days. Several studies reported that myocardial infarction may be associated with new-onset arrhythmias. In particular, some fatal arrhythmic events such as ventricular tachyarrhythmia often occur during or immediately after acute myocardial infarction [2,3]. Prolonged conventional ECG monitoring increases the detection rate of arrhythmic events [10]. Therefore, we designed the study to detect arrhythmias in patients with postmyocardial infarction, using the ATP-C120, a new patch device. This device is a single-lead ECG monitoring device that can continuously monitor the ECG signal for up to 11 days. The ATP-C120 has recently demonstrated that its diagnostic capability and safety compares to conventional ECG monitoring systems [11].

In this study, potentially fatal arrhythmias such as ventricular tachyarrhythmias or atrial fibrillation, which can produce devastating events, were scarcely detected. However, a moderate number of participants with postmyocardial infarction had nonsustained atrial tachycardia events. Several studies reported that nonsustained atrial tachycardia and paroxysmal atrial fibrillation share similar electrical stimulating pathways [12]. Other studies reported that episodes of atrial tachycardia may cause the remodeling of the pulmonary vein cardiomyocytes and the left atrium, and that atrial tachycardia is potentially related to arrhythmogenesis of paroxysmal atrial fibrillation [13]. Although in our study the device only detected 1 exact paroxysmal atrial fibrillation, a moderate number of nonsustained atrial tachycardia episodes were recorded, indicating the unstable hemodynamic and electrical impulses of the atria after myocardial infarction.

β-Blocker therapy after myocardial infarction is necessary for survival [14]. Therefore, guidelines based on randomized controlled and large observational studies recommend β-blocker therapy for all patients after myocardial infarction [15,16]. In our study, nonsustained atrial tachycardia was more frequently found in patients who were not receiving β-blocker therapy. The antiarrhythmogenic effect of β-blocker therapy may stabilize atrial electrophysiology. Therefore, this study suggests that long-term β-blocker therapy after myocardial infarction for prevention of atrial degeneration and new-onset atrial fibrillation needs to be further investigated. Interestingly, the dose of β-blocker did not affect the incidence of paroxysmal atrial tachycardia. This implies that β-blockers may be important when used at any tolerable dose after acute myocardial infarction.

This study was a comprehensive analysis of the incidence of postmyocardial infarction arrhythmias. One major limitation of our study was the small number of patients. Therefore, only a few clinically important arrhythmic events were recorded. However, this does not indicate that prolonged monitoring after myocardial infarction only shows trivial arrhythmic episodes. This study showed that there was an interestingly high incidence of supraventricular arrhythmic events. This infers the need for further investigation regarding the progression to atrial fibrillation and fatal complications after arrhythmic episodes.

A wearable ECG monitoring patch device is easy to apply and can detect ECG rhythm disturbances in patients with postmyocardial infarction. Further study is necessary regarding clinical implications and therapeutic approaches for early detected arrhythmias after myocardial infarction to prevent adverse outcomes among patients.