QRS broadening due to terminal distortion is associated with the size of myocardial injury in experimental myocardial infarction.

Introduction: Not only repolarization, but also depolarization ECG indexes reflect the progression of ischemic injury. The aim was to assess the QRS duration and morphology dynamics during the prolonged coronary occlusion and their association with the myocardial area at risk (MaR) and final infarct size (IS).

Methods: In pigs, myocardial infarction was induced by inflation of an angioplasty balloon in the left descending artery (LAD), and ECG was continuously recorded. QRS duration was calculated on a beat-to-beat basis during the occlusion period. Single photon emission computed tomography (SPECT) was performed for the assessment of MaR, and IS was assessed by magnetic resonance imaging (MRI).

Results: All animals developed an anteroseptal infarction with MaR 40±9% and IS 23±7%. Two peaks of QRS widening were found in all animals: the early peak immediately after LAD occlusion and the late one 17.7±4.1min later. No association was found between MaR and IS and either QRS width or the degree of QRS widening at the early peak. QRS duration on the late peak correlated with both MaR (r=0.61; p=0.007) and IS (r=0.55; p=0.018).

Conclusion: The QRS widening at the late peak, but not at the early peak, is associated with the size of myocardial injury, suggesting different underlying mechanisms.