High-resolution and signal-averaged electrocardiography to separate post-myocardial infarction patients with and without ventricular tachycardia

High-resolution and signal-averaged ECG, 24 h Holter recordingand ejection fraction were used to separate post-myocardialinfarction patients with and without ventricular tachycardia(VT) among 150 individuals: 26 patients with an old myocardialinfarction and documented sustained VT, 104 patients with anacute myocardial infarction without sustained VT, who were followed-upfor 2 years, and 20 healthy volunteers. Bipolar orthogonal XYZleads were recorded, high-pass filtered at cut-off frequenciesof 25, 40, 60, 80 and 100 Hz, and combined to vector magnitudex² + Y²+ Z². The filtered QRS duration, the root-mean-squarevoltages of different time intervals and the durations of lowamplitude signals under different thresholds, both from theinitial and terminal QRS, were calculated. The sensitivity andspecificity of each parameter alone and in every combinationof two, three and four parameters (17 million different combinations)were computed both from non-averaged and averaged data. Thebest separation was achieved by 12 combinations all includingfour signal-averaged ECG parameters, with a sensitivity of 81%and a specificity of 79%. The parameters represented most were:filtered QRS duration at 25 Hz, RMS voltage of the last 50 msat 25 Hz, terminal LAS duration at 80 Hz, and RMS voltage ofthe last 20 ms at 80 Hz. Parameters of the initial QRS complexdid not improve either the sensitivity or the specificity ofthe method. In logistic regression analysis, the best combinationsof four signal-averaged ECG parameters separated VT patientsbetter (P<0·001) than non-sustained ventricular tachycardiaat Holter (P=0·001); left ventricular ejection fraction(P=0·01) or age (P=0·006). Parameters calculatedfrom averaged data gave better results than parameters calculatedfrom non-averaged data.