Decline in inducibility of sustained ventricular tachycardia from two to twenty weeks after acute myocardial infarction

To determine temporal evolution of sustained ventricular arrhythmias inducible after acute myocardial infarction (AMI), serial programmed ventricular stimulation (PVS) was performed in 27 patients 15 ± 4 and 150 ± 28 days after AMI. These patients did not have worsening of congestive heart failure or angina, coronary artery bypass surgery or spontaneous sustained ventricular tachycardia (VT) in the period between 2 PVS studies. During initial PVS, sustained VT or ventricular fibrillation (VF) was inducible in 17 patients (group I) and was not inducible in 10 (group II). Late PVS in group I induced sustained VT or VF in 8 patients (47%) and nonsustained VT or no VT in 9 (53%). A decrease in late inducibility of sustained VTVF was greater for arrhythmias induced during initial PVS by triple extrastimuli and burst pacing than for those induced by double extrastimuli (88% vs 25%, p < 0.04), but appeared to be unrelated to the morphologic characteristics or cycle length of the initially induced sustained VT or VF and to other clinical, hemodynamic or angiographic variables. During late PVS in 10 group II patients, sustained VT or VF remained noninducible in 9 (90% concordance); in 1 patient sustained VT was induced. During a mean follow-up of 14 ± 5 months since late PVS, none of 27 patients had spontaneous sustained VT and 2 patients in group I died suddenly. Thus, in survivors of AMI, inducibility of sustained VT or VF decreased by half during late PVS performed 5 months after the index AMI, but noninducibility 2 weeks after AMI had a high long-term reproducibility. These findings indicate the presence of an unstable electrophysiologic substrate in the first 3 to 6 months after AMI and should be taken into consideration when interpreting the results of PVS in patients with relatively recent myocardial infarction.