br Role of ICD treatment In patients

Role of ICD treatment In patients with VT associated with various structural Aminoallyl-UTP diseases, ICD therapy is recommended even if the target VT is successfully ablated and no VT is inducible after catheter ablation [29]. This is because, in such patients, the same VT and/or new VT recurs during the follow-up period because of the presence of an arrhythmogenic myocardium in the heart and/or progression of the underlying heart diseases (prior myocardial infarction, idiopathic dilated cardiomyopathy, arrhythmogenic RV dysplasia, or cardiac sarcoidosis). In addition, ICD therapy is also recommended for primary prevention of sudden cardiac death in patients with an impaired left ventricular function (which is usually indicated by a lower left ventricular ejection fraction of <30–35%) without clinically documented VTs [29–31]. On the other hand, in patients after ToF repair, the left ventricular ejection fraction is usually preserved, although myocardial hypertrophy and/or dilation of the right ventricle persists and could work as an arrhythmogenic substrate long after successful catheter ablation. Therefore, it is reasonable that ICD therapy is recommended in patients with aborted sudden cardiac death and/or ventricular fibrillation. ICD therapy is also recommended in patients in whom programmed electrical stimulation induces nonclinically documented microreentrant and/or nonreentrant VT in addition to the clinically documented macroreentrant VT. In such patients, the arrhythmogenic substrate might be extensively present in the heart. However, indication of ICD therapy is controversial in patients in whom hemodynamically stable clinically documented macroreentrant VT is successfully treated and no other VT is inducible after catheter ablation. We encountered few such patients (Case 1) because these patients were treated before ICD devices were available in our country. Although the clinical outcomes of these patients have been uneventful, supplemental treatment with ICDs may be necessary in such patients because recurrences of VT after successful catheter ablation have been reported. Unlike that for secondary prevention, the effectiveness of ICD therapy and/or catheter ablation for primary prevention of sudden cardiac death has not yet been established. Although several factors (left and/or RV dysfunction, late corrective surgery, a wider QRS width, and presence of pulmonic valve regurgitation and/or RVOT stenosis) have been proposed as future risks of cardiac events in patients after ToF repair [4,32–35], the risk evaluation method and/or therapeutic approach (using ICDs, catheter ablation, or antiarrhythmic drugs) for primary prevention of sudden cardiac death should be studied further.
Summary and conclusions
Conflict of interest
Introduction Ventricular tachycardia (VT) and ventricular fibrillation (VF) leading to sudden cardiac death (SCD) are responsible for significant morbidity and mortality in patients with myocardial infarction (MI). Identification of MI patients who are prone to VT/VF allows for an indication of implantable cardioverter-defibrillator (ICD) placement. For this purpose, there has been an increase in research on the noninvasive risk stratification of lethal ventricular arrhythmias and SCD. To date, various noninvasive methods such as signal-averaged electrocardiography (SAECG) [1–4], microvolt T-wave alternans (MTWA) [5–7], heart rate variability (HRV) [8–10], and heart rate turbulence (HRT) [11,12] have been developed, and currently, MTWA and SAECG are widely used for risk stratification in patients with prior MI.
Microvolt T-wave alternans (MTWA) Recently, an alternative method of measuring T-wave alternans, the time-domain modified moving average (MMA) method, has been developed [25]. The MMA method applies the noise-reduction principle of signal averaging. The T-wave amplitude and morphology of odd and even beats were averaged for each 15-s period and were superimposed, and the maximum difference of each median complex was reported as the T-wave alternans values. The MMA method allows MTWA analysis during routine 24-h Holter monitoring, and a number of studies have suggested its utility for predicting malignant ventricular arrhythmias, SCD, and cardiovascular and total mortality [25–33]. The Finnish Cardiovascular Study demonstrated that the NPV of the MMA method for SCD was 98.6%, which was comparable to the results of a meta-analysis with the spectral method [26,34]. The MMA method may be superior to the spectral method in that the MMA method does not require a special protocol for maintaining the stationary heart rate. Taken together, an increasing amount of data suggests that the MTWA test is a promising risk stratifier of malignant ventricular arrhythmias. It is currently recommended as a Class IIa, Level of Evidence A risk-stratification tool among post-MI patients [35].