[Signal averaged ECG and mechanisms of sudden death].

The aim of signal averaged electrocardiography is to detect late potentials (LP) which are markers of ventricular tachycardia. As sudden death is often due to ventricular fibrillation which can complicate ventricular tachycardia, some workers have suggested that the presence of LP may increase the risk of sudden death. We analysed the results of signal averaged ECG in 17 subjects who died suddenly and compared them with 8 patients who died from ventricular tachycardia. These two groups of patients were part of a general population of 450 subjects who underwent programmed ventricular stimulation and signal averaged ECG by Simson's method (25 Hz filter). Three parameters of this ECG were analysed: total QRS duration (Dur QRS), amplitude of the signal 40 ms before its termination (V 40), and the duration of the terminal activity less than 40 microV (Dur LP). The criteria of diagnosis of Lp were: Dur QRS greater than or equal to 120 ms, V 40 less than or equal to 20 microV, Dur LP greater than or equal to 40 ms. The results of signal averaged ECG of patients who died suddenly were different to those of patients who died from VT: Dur QRS 116 +/- 40 vs 140 +/- 25 ms, V 40 27 +/- 24 vs 7 +/- 8 microV, Dur LP 39 +/- 27 vs 59 +/- 14 ms. Only 8 patients who died suddenly had LP (47%) whereas all patients who died of VT had LP. A correlation was observed between the presence of LP and 2 factors: the LV ejection fraction which was significantly lower in patients with LP (28 +/- 8 vs 46 +/- 19%) and the results of programmed ventricular stimulation: patients with induced sustained VT less than 270/mn usually had LP (15/16). LP were usually absent (4/6) in cases of ventricular flutter (VT greater than or equal to 270/mn) or induced VF. The presence of LP in 2 patients could signify a risk of developing VT later on. In conclusion, 9/17 patients who died suddenly did not have LP. The risk of sudden death due to primary VF or V flutter cannot be predicted. Other causes of VF are even harder to identify.