Utility of microvolt T-wave alternans to predict sudden cardiac death in patients with cardiomyopathy

Prognostic Evaluation of Microvolt T-Wave Alternans in Hypertrophic Cardiomyopathy: 9-year Clinical Follow-up

BACKGROUND

Sudden cardiac death (SCD) resulting from ventricular arrhythmia is the main complication of hypertrophic cardiomyopathy (HCM). Microvolt T-wave alternans (MTWA) is associated with the occurrence of ventricular arrhythmias in several heart diseases, but its role in HCM remains uncertain.

OBJECTIVE

To evaluate the association of MTWA with the occurrence of SCD or potentially fatal ventricular arrhythmias in HCM patients in a long-term follow-up.

METHODS

Patients diagnosed with HCM and NYHA functional class I-II were consecutively selected. At the beginning of the follow-up, the participants performed the MTWA evaluation using the modified moving average during the stress test. The results were classified as altered or normal. The composite endpoint of SCD, ventricular fibrillation, sustained ventricular tachycardia (SVT) or appropriate implantable cardiac defibrillation (ICD) therapy was assessed. The level of significance was set at 5%.

RESULTS

A total of 132 patients (mean age of 39.5 ± 12.6 years) were recruited and followed for a mean of 9.5 years. The MTWA test was altered in 74 (56%) participants and normal in 58 (44%). Nine events (6.8%) occurred during the follow-up, with a prevalence of 1.0%/year - six SCDs, two appropriate ICD shocks and one episode of (SVT). Altered MTWA was associated with non-sustained ventricular tachycardia on Holter (p = 0.016), septal thickness ≥30 mm (p < 0.001) and inadequate blood pressure response to effort (p = 0.046). Five patients with altered MTWA (7%) and four patients with normal MTWA (7%) had the primary outcome [OR = 0.85 (95% CI: 0.21 - 3.35, p=0.83)]. Kaplan-Meir event curves showed no differences between normal and altered MTWA.

CONCLUSION

Altered MTWA was not associated with the occurrence of SCD or potentially fatal ventricular arrhythmias in HCM patients, and the low rate of these events during long-term follow-up suggests the good prognosis of this heart disease.

Inhibition of Ca2+-dependent protein kinase C rescues high calcium-induced pro-arrhythmogenic cardiac alternans in rabbit hearts

Cardiac alternans closely linked to calcium dysregulation is a crucial risk factor for fatal arrhythmia causing especially sudden death. Calcium overload is well-known to activate Ca²⁺-dependent protein kinase C (PKC); however, the effects of PKC on arrhythmogenic cardiac alternans have not yet been investigated. This study aimed to determine the contributions of PKC activities in cardiac alternans associated with calcium cycling disturbances. In the present study, action potential duration alternans (APD-ALT) induced by high free intracellular calcium ([Ca²⁺]_i) exerted not only in a calcium concentration-dependent manner but also in a frequency-dependent manner. High [Ca²⁺]_i-induced APD-ALT was suppressed by not only BAPTA-AM but also nifedipine. On the other hand, PKC inhibitors BIM and Gö 6976 eliminated high [Ca²⁺]_i-induced APD-ALT, and PKC activator PMA was found to induce APD-ALT at normal [Ca²⁺]_i condition. Furthermore, BIM effectively prevented calcium transient alternans (CaT-ALT) and even CaT disorders caused by calcium overload. Moreover, BIM not only eliminated electrocardiographic T-wave alternans (TWA) caused by calcium dysregulation, but also lowered the incidence of ventricular arrhythmias in isolated hearts. What's more, BIM prevented the expression of PKC α upregulated by calcium overload in high calcium-perfused hearts. We firstly found that pharmacologically inhibiting Ca²⁺-dependent PKC over-activation suppressed high [Ca²⁺]_i-induced cardiac alternans. This recognition indicates that inhibition of PKC activities may become a therapeutic target for the prevention of pro-arrhythmogenic cardiac alternans associated with calcium dysregulation.

Presumed arrhythmic death in consecutive survivors of acute myocardial infarction--implications for primary implantable cardioverter defibrillator implantation

AIM

To describe the occurrence of arrhythmic death among survivors of acute myocardial infarction (AMI) and the availability of a primary implantable cardioverter defibrillator (ICD).

METHODS

Consecutive patients who fulfilled the criteria for AMI admitted to the Sahlgrenska University Hospital during 21 months were prospectively followed for 2 years with a focus on echocardiography and mode of death.

RESULTS

Among the 471 patients, for whom information on ejection fraction (EF) was available and who survived the first week, 10 patients died between days 7 and 30 - of whom one had an arrhythmic death. Among the 461 survivors on day 30, 34 patients (7.4%) had an EF of 30% or less. Among these, 24 were judged to be available for ICD implantation, of whom one died an arrhythmic death during follow-up. Among the remaining 10 patients who were excluded from ICD indication because of either high age and/or severe comorbidity, two patients died an arrhythmic death. Among the remaining 427 patients who had an EF greater than 30%, six died an arrhythmic death. Thus, 10 patients, with EF assessed, died an arrhythmic death between day 7 and 2 years after AMI, but only one would have received an ICD according to the Multicenter Automatic Defibrillator Implantation Trial II criteria and clinical judgement.

CONCLUSION

Of the 471 consecutive survivors of AMI, 10 (2%) died an arrhythmic death, of whom only one would have received an ICD according to current guidelines and clinical judgement. Predictors of subsequent arrhythmic death after an AMI, useful on a per patient basis, remain an unmet need.

T-wave alternans and sudden cardiac death

Sudden cardiac death (SCD) is the leading cause of mortality in patients with ischemic heart disease and left ventricular dysfunction. The majority of SCD are due to ventricular tachyarrhythmias. SCD strikes many asymptomatic patients and often is the first manifestation of heart disease. Thus, reliable determination of arrhythmic risk is warranted to guide preventive therapy. To highlight the prognostic value of microvolt-level electrical alternans of the T-wave (MTWA) in patients at risk for SCD, most of the pertinent published articles in the Medline, Scopus, and EBSCO Host research databases have been reviewed. MTWA has been proposed to be a strong and independent predictor of all-cause and arrhythmic mortality. The high predictive value of MTWA in patient with cardiomyopathy varies significantly depending on the population studied. Combining with other indices or having serial MTWA readings could overcome MTWA limitations. Redefining MTWA readings may expand its prognostic utility.