MICROVOLT T-WAVE ALTERNANS - ITS CLINICAL SIGNIFICANCE IN THE ASSESSMENT OF THE RISK OF SUDDEN CARDIAC DEATH AMONG PATIENTS WITH HYPERTROPHIC CARDIOMYOPATHY
Background: Some patients with hypertrophic cardiomyopathy (HCM) are at significant risk of premature sudden death. Identification of the risk factors may enable effective prevention of adverse cardiac events in these patients. Assessment of the microvolt T-wave alternans (MTWA) is a recognized non-invasive diagnostic test used in risk stratification of sudden cardiac death (SCD). However, the number of reports on the frequency of occurrence of MTWA in HCM is small.
Aim: Evaluation of the prognostic value of MTWA in predicting the risk of arrhythmic events (sudden cardiac death, documented VT/VF, appropriate ICD discharge) in patients with HCM.
Methods: 122 patients with HCM underwent detailed clinical assessment and ECG- and echocardiographic examination. They underwent 24-hour ambulatory ECG monitoring, and the following elements were analysed: 1) arrhythmias, 2) heart rate variability (HRV) and the QT segment, 3) the presence of ventricular late potentials (LP), 4) heart rate turbulence (HRT). MTWA assessment was made during a test on a treadmill (Cambridge Heart). In accordance with the adopted criteria, the test was interpreted as negative, positive or indeterminate. Subsequently, positive and indeterminate results were described collectively as MTWA(+) and negative results as MTWA(-). Then the patients were divided into two groups: Group 1 – 57 patients (46,7%) with MTWA(-), and Group 2 – 65 patients (53,2%) with MTWA(+). In order to stratify the risk, the following were adopted as composite primary endpoints: sudden cardiac death or hospitalization for life-threatening arrhythmias (VT/VF), and appropriate ICD discharge.
Results: The mean follow-up period of the patients was 57±8 months; during that time, events that met the criteria for the endpoint occurred in 16 patients. On the basis of univariate analysis, 10 variables with a significant influence on the occurrence of an event were selected (unexplained syncope, NT-proBNP values elevated above 411 pg/ml, size of the left atrium over 44mm, diastolic thickness of the interventricular septum over 25 mm, the presence of MTWA(+), the QRS width>90 msec, QTc>467 msec, QTd>70 msec, SDNN<110 msec, and sinus rhythm turbulence parameters TS<2,9 ms/2RR). These variables were then included in a multivariate analysis. The model from a Cox regression analysis showed that the presence of unexplained syncope (HR = 1,4), MTWA(+) (HR=1,5), size of the left atrium over 44mm (HR=5), and the thickness of the interventricular septum over 25 mm (HR=1,5) increased the risk of sudden events.
- Patients with hypertrophic cardiomyopathy had a significant percentage of positive results of the microvolt T-wave alternans test (MTWA+),
- Positive MTWA test result in patients with hypertrophic cardiomyopathy can help to identify patients at risk of sudden cardiac death.