Absence of change of signal-averaged electrocardiogram identifies patients with ventricular arrhythmias who are non-responders to amiodarone

Abstract

Objectives: The aim of this study was to assess the ability of a non-invasive study, the signal-averaged ECG (SAECG), to predict the effect of amiodarone at ventricular level. Background: Amiodarone is the main drug drug used in the treatment of ventricular arrhythmias. Standard ECG does not detect any change in QRS complex resulting from amiodarone therapy. SAECG is more sensitive than ECG for detecting changes in QRS complex. Methods: The study examined the effects of amiodarone on SAECG in relation to the results of programmed ventricular stimulation in 68 patients with old myocardial infarction, spontaneous and inducible sustained ventricular tachycardia (VT). Results: Amiodarone prolonged the total QRS duration (dur) (129±28 vs. 140±30 ms, P<0.05) and low amplitude signal (LAS) dur (45±20 vs. 51±20 ms, P<0.1), whereas the root-mean-square voltage of the last 40 ms of QRS complex (RMS 40) was significantly reduced (20±16 vs. 14±9 μV, P<0.05). Changes in SAECG parameters did not differ significantly in patients in whom amiodarone prevented the inducibility of VT ( n=15) and those in whom VT remained inducible with amiodarone ( n=53), but in baseline QRS duration was significantly shorter in patients in whom amiodarone prevented the VT induction (118±26 vs. 133±28 ms, P<0.05). In patients in whom amiodarone did not prolong the cycle length of VT ( n=15), SAECG did not change significantly (QRS dur 131±29 vs. 132±27 ms, LAS 42±20 vs. 42±19 ms, RMS 40 22±14 vs. 19±11 μV). Comparison of the SAECG data in patients with no inducible VT and those with slowed VT differed significantly ( P<0.05) between the control state and the recording with amiodarone. Conclusions: The effects of amiodarone on VT inducibility are predicted by a shorter baseline QRS duration and the degree of drug-induced prolongation of filtered QRS duration. Amiodarone prolonged the QRS duration, LAS duration and decreased RMS 40; this effect was more important in patients with no inducible VT and in those with only slowed VT, than in patients with unchanged or accelerated VT. The absence of changes of QRS duration predicted the induction of a more rapid or not slowed VT with amiodarone with a sensitivity of 87% and a specificity of 83%. Therefore, SAECG appears as an useful and simple means to predict the effects of amiodarone in patients with myocardial infarction and VT.