Evolution of QRS duration after myocardial infarction: Clinical consequences

The natural history of late potentials after acute myocardial infarction (A MI) has been studied in the first 2 years following myocardial infarction ( MI). The purpose of the study was to assess the influence of some time dela ys since MI, including a time delay longer than 2 years on signal-averaged ECG (SAECG). SAECG was recorded at 40-Hz high pass filtering in 40 patients 10 days after acute MI (SAECG 2), then repeated 6-12 months later (mean 9 +/- 3 months) (SAECG 2), and then, 2-4 years later (mean 3 +/- 2 years) (SA ECG 3). QRS duration, root mean square voltage of the last 40 ms of QRS (RM S 40), and low amplitude signal duration (LAS) were measured at the first ( 1), second (2), and third recording (3). Results: (***P < 0.001) [GRAPHICS] The analysis of individual results showed a lengthening QRS duration at the third recording only in patients who had a decreased left ventricular ejec tion fraction (LVEF) at the third recording. In 12 patients with LVEF > 40% , QRS duration did not change at the first and third recording (104 +/- 15 vs 101 +/- 12 ms). In ail 28 patients, but one with LVEF ( 40%, QRS duratio n increased from 107 +/- 12 to 128 +/- 28 ms***. There was no correlation b etween QRS duration and LVEF at the second recording and no correlation bet ween QRS duration increase at the third recording and the presence or not o f late potentials at the first recording. QRS duration lengthening at the t hird recording was significantly correlated with a left ventricular (LV) di latation occurrence at the two-dimensional echocardiogram. All arrhythmic e vents, but two, occurred in patients who developed a QRS duration prolongat ion and were significantly correlated (P < 0.01) to a mean longer QRS durat ion (132 +/- 20 ms) than in patients without arrhythmic events (113 +/- 27 ms). In conclusion, the patients with a LV impairment, and who developed a LV dilatation several months after AMI, presented a delayed lengthening of QRS duration noted only at least 2 years after infarction. These patients a re at risk of arrhythmic events.