Background: Sudden cardiac death (SCD) mostly resulting from ventricular arrhythmia remains a cause of mortality in 19-30% of adults with congenital heart defects. Indications for implantable cardioverter-defibrillators in primary prophylaxis are still under research. MicrovoltT wave alternans (MTWA) is one of the SCD risk stratification methods. We determined the incidence of MTWA in these patients and its coincidence with ventricular arrhythmia, as well as risk factors of ventricular arrhythmia/SCD.
Methods: 204 patients with complex congenital heart anomalies and 45 healthy volunteers underwent ambulatory ECG monitoring, a cardiopulmonary test, B-type natriuretic peptide assessment, echocardiography and an MTWA test. After excluding technically inadequate traces, the remaining 179 patients and 43 controls were classified into MTWA positive (+), negative (-) and indeterminate (ind) subgroups. Additionally, MTWA (+) and MTWA (ind) formed an 'abnormal' group, labeled MTWA (non-).
Results: Abnormal MTWA was observed more frequently in the study group compared to controls (59 [33.0%] vs. 1 [2.3%], p = 0.000001). The MTWA (non-) group compared to MTWA (-) presented a higher number of males (61.0% vs. 37.5%, p = 0.005), predominance of patients with NYHA > I (44.1% vs. 25.0%, p = 0.007), pulmonary hypertension (16.9% vs. 0.8%, p = 0.00007), lower blood saturation (97% [73-100] vs. 99% [69-100], p = 0.0003), higher incidence of malignant arrhythmia (9 [15.2%] vs. 3 [2.5%], p = 0.003), lower peak oxygen consumption VO2 [mL/kg/min] (23.1 ± 5.9 vs. 26.3 ± 6.7, p = 0.002), higher VE//VCO2 slope (36.0 [25-74] vs. 31.0 [21-58], p = 0.01). Multivariate logistic regression analysis proved that pulmonary hypertension (OR = 13.7, p = 0.03), male gender (OR = 10.4,p = 0.00002), VE/VCO2 slope (OR = 1.07, p = 0.045) and VO2 (OR = 0.89, p = 0.04) increase the probability of MTWA (non-).
Conclusions: Abnormal MTWA is more frequent in adults with congenital heart diseases than in the healthy population. Its probability increases in patients demonstrating clinical findings conducive to lethal arrhythmia like heart failure and pulmonary hypertension.