Continuous multi-day tracking of post-myocardial infarction recovery of cardiac electrical stability and autonomic tone using electrocardiogram patch monitors

Abstract

Background: Sudden cardiac death (SCD) risk is elevated following acute myocardial infarction (MI). The time course of SCD susceptibility post-MI requires further investigation.

Methods: In this observational cohort study, we employed state-of-the-art noninvasive ECG techniques to track the daily time course of cardiac electrical instability and autonomic function following ST-segment elevation myocardial infarction (STEMI) and non-STEMI (NSTEMI). Preventice BodyGuardian MINI-EL Holters continuously recorded ECGs for 7 days at hospital discharge and at 40 days for STEMI (N = 5) or at 90 days for NSTEMI patients (N = 5). Cardiac electrical instability was assessed by T-wave alternans (TWA) and T-wave heterogeneity (TWH); autonomic tone was determined by rMSSD-heart rate variability (HRV).

Results: TWA was severely elevated (≥60 μV) in STEMI patients (80 ± 10.3 μV) at discharge and throughout the first recording period but declined by 50% to 40 ± 2.3 μV (p = .03) by Day 40 and remained in the normal range (<47 μV). TWH, a related phenomenon analyzed from 12-lead ECGs, was reduced by 63% in the five STEMI patients from discharge to normal (<80 μV) at follow-up (105 ± 27.3 to 39 ± 3.3 μV, p < .04) but increased by 65% in a STEMI case (89 to 147 μV), who received a wearable defibrillator vest and later implantable cardioverter defibrillator. In NSTEMI patients, TWA was borderline abnormal (47 ± 3.3 μV) at discharge and declined by 19% to normal (38 ± 1.2 μV) by Day 90 (p = .05). An overall reciprocal increase in rMSSD-HRV suggested recovery of vagal tone.

Conclusions: This study provides proof-of-principle for tracking post-MI SCD risk in individual patients with implications for personalized therapy.

Keywords: ST-elevation myocardial infarction; T-wave alternans; T-wave heterogeneity; heart rate variability; non-ST-elevation myocardial infarction.

FIGURE 1

Illustration of the Preventice BodyGuardian MINI‐EL Holter and its placement on the torso in the V₄, V₅, and V₆ regions to optimize T‐wave alternans detection (Verrier et al., 2011)

FIGURE 2

QRS‐aligned templates showing T‐wave alternans (TWA) in representative ST‐elevation myocardial infarction (STEMI) (upper panel) and non‐ST‐elevation myocardial infarction (NSTEMI) patients (lower panel) on the first day after hospital discharge. In the STEMI patient, TWA was 79 μV, which was severely abnormal (≥60 μV). In the NSTEMI patient, TWA was 49 μV, which is above the cutpoint of abnormality (≥47 μV) but was 38% lower than in the STEMI patient

FIGURE 3

Time course of changes in T‐wave alternans (TWA) and heart rate variability (HRV) by analysis of square root of the mean of the sum of squares of differences between adjacent normal RR intervals (rMSSD) in five ST‐elevation myocardial infarction (STEMI) patients (group data). Upper panel: TWA was severely abnormal (≥60 μV) during the first 7 days after discharge but declined significantly to the normal range (<47 μV) by day 40, indicating a lowered level of risk for cardiac arrhythmias, and remained in the normal range during the second recording session. Lower panel: rMSSD‐HRV trended toward an increase during both recording periods. *p < .05 compared with discharge day

FIGURE 4

Time course of changes in T‐wave alternans (TWA) and heart rate variability (HRV) by analysis of square root of the mean of the sum of squares of differences between adjacent normal RR intervals (rMSSD) in five non‐ST‐elevation myocardial infarction (NSTEMI) patients (group data). Upper panel: TWA was in the borderline abnormal range (~47 μV) during the first recording period and in the normal range (<47 μV) during the second recording period, indicating a lowered level of risk for cardiac arrhythmias. Lower panel: A reciprocal increase in rMSSD‐HRV was prominent during the second follow‐up visit during a significant decline in TWA. *p < .05 compared with discharge day

FIGURE 5

Pattern of recovery of T‐wave heterogeneity (TWH) in the ST‐elevation myocardial infarction (STEMI) case who required a wearable defibrillator vest and implantable cardioverter defibrillator (ICD) (open bar) compared with STEMI patients (n = 5) without clinical indications for a vest or ICD (filled bar). At hospital discharge, TWH was abnormal (>80 μV) at 89 μV in the STEMI case. At the 40‐day follow‐up, TWH had increased by 65% to 147 μV. By comparison, in the five STEMI patients without indications for a vest or ICD, TWH was elevated (105 ± 27.3 μV) at hospital discharge. In the three patients with 12‐lead ECGs at the 40‐day follow‐up, TWH decreased by 63% to normal levels (39 ± 3.3 μV, *p < .04). Data are reported as means ± SEM

FIGURE 6

Time course of heart rate in ST‐elevation myocardial infarction (STEMI) (upper panel) and non‐ST‐elevation myocardial infarction (NSTEMI) patients (lower panel). Heart rate was remarkably stable from day to day in both groups, likely due to the fact that all patients were receiving beta‐blockade therapy