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

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.

Quantitative T-wave alternans analysis for guiding medical therapy: an underexploited opportunity

Reducing the toll of sudden cardiac death (SCD) remains a major challenge in cardiology, as it is the leading cause of adult mortality in the industrially developed world, claiming 310,000 lives annually in the United States alone. The main contemporary noninvasive index of cardiovascular risk, left ventricular ejection fraction (LVEF), has not proved adequately reliable, as the majority of individuals who die suddenly have relatively preserved cardiac mechanical function. Monitoring of T-wave alternans (TWA), a beat-to-beat fluctuation in ST-segment or T-wave morphology, is an attractive approach to risk stratification on both scientific and clinical grounds, as this ECG phenomenon has been shown using the FDA-cleared Spectral and Modified Moving Average methods to assess risk for cardiovascular mortality including SCD in studies enrolling >12,000 individuals with depressed or preserved LVEF. The evidence supporting TWA as a therapeutic target is reviewed.

Relation of T-wave alternans to mortality and nonsustained ventricular tachycardia in patients with non-ST-segment elevation acute coronary syndrome from the MERLIN-TIMI 36 trial of ranolazine versus placebo

We explored the utility of T-wave alternans (TWA) in predicting mortality in patients with non-ST-segment elevation acute coronary syndrome (NSTEACS). Maximum TWA was calculated using Modified Moving Average method from continuous electrocardiographic recordings in patients with left ventricular ejection fraction <40% and ventricular tachycardia (VT) ≥4 beats during index hospitalization or sudden cardiac death during the follow-up year and age- and sex-matched controls in the Metabolic Efficiency with Ranolazine for Less Ischemia in Non-ST Elevation Acute Coronary Syndrome-Thrombolysis In Myocardial Infarction (MERLIN-TIMI) 36 trial. All patients received standard therapy for NSTEACS plus ranolazine (n = 109) or placebo (n = 101). Median follow-up was 1 year. Baseline clinical characteristics did not differ between patients with elevated TWA (≥47 μV) compared with lower levels. Patients with TWA ≥47 μV at admission had increased risk of total mortality (adjusted odds ratio [ORadj] 2.35, p = 0.04) during follow-up and VT ≥4 beats (ORadj 2.70, p = 0.01) during hospitalization with a trend toward increased cardiovascular death risk (ORadj 2.18, p = 0.07) during follow-up. In patients receiving placebo, TWA ≥47 μV on day 6 was associated with increased risk of total mortality (OR 4.12, 95% confidence interval 1.25 to 13.64, p = 0.02) and cardiovascular death (OR 4.73, p = 0.01) during follow-up. No deaths occurred among patients with TWA ≥47 μV assigned to ranolazine. In conclusion, in patients with NSTEACS and left ventricular ejection fraction <40%, TWA ≥47 μV early after admission is associated with increased risk of mortality at 1 year and with nonsustained VT during hospitalization. TWA may be useful in risk estimation in patients with NSTEACS. The possibility that TWA may serve as a therapeutic target deserves further exploration.

Time-domain T-wave alternans is strongly associated with a history of ventricular fibrillation in patients with Brugada syndrome

AIMS

T-wave alternans (TWA) is an indicator of vulnerability to ventricular arrhythmias and is useful for predicting sudden cardiac death (SCD) in patients with various structural heart diseases. We evaluated whether high levels of time-domain TWA on ambulatory ECG (AECG) are associated with a history of ventricular fibrillation (VF) in Brugada syndrome (BrS) patients.

METHODS AND RESULTS

We examined the associations among VF history, family history of SCD, spontaneous type 1 electrocardiogram (ECG), late potentials, VF induction by programmed electrical stimulation, and TWA in 45 BrS patients (44 males; mean age, 45 ± 15 years). TWA analyzed from 24-h AECG recordings using the modified moving average method was positive in 13 of 43 patients (30%). Patients with a history of VF had a significantly higher incidence of a positive TWA test (82% vs. 13%; P < 0.001) and spontaneous type 1 ECG (92% vs. 38%; P = 0.007) than those without VF history. Multivariate analysis indicated that positive TWA (OR 7.217; 95% CI 2.503-35.504; P = 0.002) and spontaneous type 1 ECG (OR 5.530; 95% CI 1.651-34.337; P = 0.020) were closely associated with VF history. Spontaneous type 1 ECG had high sensitivity (92%) but low specificity (63%). Positive TWA was a reliable marker with high sensitivity and specificity (82% and 88%, respectively).

CONCLUSION

Elevated time-domain TWA on AECG confirms arrhythmia risk in symptomatic BrS patients without the need for provocative stimuli.

T-wave alternans as an arrhythmic risk stratifier: state of the art

Microvolt level T-wave alternans (MTWA), a phenomenon of beat-to-beat variability in the repolarization phase of the ventricles, has been closely associated with an increased risk of ventricular tachyarrhythmic events (VTE) and sudden cardiac death (SCD) during medium- and long-term follow-up. Recent observations also suggest that heightened MTWA magnitude may be closely associated with short-term risk of impending VTE. At the subcellular and cellular level, perturbations in calcium transport processes likely play a primary role in the genesis of alternans, which then secondarily lead to alternans of action potential morphology and duration (APD). As such, MTWA may play a role not only in risk stratification but also more fundamentally in the pathogenesis of VTE. In this paper, we outline recent advances in understanding the pathogenesis of MTWA and also the utility of T-wave alternans testing for clinical risk stratification. We also highlight emerging clinical applications for MTWA.