**4. ECG measurements**

Classically, the presence of Left Bundle Branch Block (LBBB) was considered of major prog‐ nostic importance, associated with the occurrence of sudden death in patients with ischemic heart disease. This was based on earlier studies, most of them performed before the era of percutaneous coronary revascularization [39].

In more recent investigations, especially those resulting from secondary analyses of MUSTT and MADIT-II trials, it has become clear that QRS prolongation is related with mortality af‐ ter MI, although the magnitude of the relationship between abnormal intraventricular con‐ duction and SCD in CHD remains unclear [40].

In an analysis of MUSTT trial, the authors noted that patients with LBBB had lower ejection fractions and higher incidence of symptomatic heart failure, suggesting that the increase in overall mortality was probably due to a sicker population [41].

In the MADIT-II cohort with prolonged QRS its duration (QRSd) was found to be an inde‐ pendent predictor of SCD in medically managed patients (HR 2.12) but not in ICD-treated patients (HR 0.77).This was attributed to the fact that ICD-treated MADIT II patients died predominantly of non-sudden HF, and QRSd would not predict HF mortality [42]

In the cardiac resynchronization therapy trial (MADIT-CRT), CRT dramatically reduces the progression of HF in patients with a low ejection fraction and a wide QRS complex. QRS du‐ ration and morphology was considered an important prognostic factor indicating more ad‐ vanced cardiac pathology [43].

Other electrocardiographic parameters in which the prognostic value was evaluated were T-wave alternant (MTWA), the signal-averaged ECG (SAECG) and QT parameters and dynamics [44].

One of the parameters with more consistent results was MTWA. TWA consist of a fluctua‐ tion of the amplitude or morphology of the T wave every other beat assessed during exer‐ cise testing or atria pacing [45].

A positive MTWA determined an approximately 2.5-fold higher risk of cardiac death and life-threatening arrhythmia and showed a very high negative predictive value both in ische‐ mic [46] and no ischemic patients . According to guidelines, it is a recommendation class IIa the use of TWA to improve the diagnosis and risk stratification of patients with ventricular arrhythmias [14].

In a small study in patients post-MI and EF less than or equal to 30%, microvolt TWA was better than QRS duration at identifying a high-risk group and also a low-risk group unlikely to benefit from ICD therapy [47].

SAECG permits the identification of low-amplitude signals (microvolt level) at the end of the QRS complex referred to as late potentials. These indicate regions of abnormal myocar‐ dium with slow conduction believed to serve as markers of the substrate for reentrant ven‐ tricular tachyarrhythmias [48]. It has a high negative predictive value but its value is lower after coronary revascularization. [49]
