Evaluation of a QRS scoring system in acute myocardial infarction: Relation to infarct size, early stage left ventricular ejection fraction, and exercise performance

Recent studies suggest that the QRS scoring system (QRSs) using observations of Q- and R-wave duration and R Q and R S amplitude ratios in the standard electrocardiogram (ECG) is useful in estimating left ventricular function after acute myocardial infarction (AMI). The correlation of QRSs with infarct size determined by serum creatine kinase MB changes and early stage left ventricular ejection fraction (LVEF) determined by multiple gated equilibrium cardiac blood pool scintigraphy was studied in 32 patients with AMI using ECGs taken 3 and 7 days after onset. The relation of QRSs to exercise performance was also examined in 45 other patients who underwent heart rate limited low level exercise test (LLET) soon after AMI (12.3 ± 5.6 days, mean ± standard deviation). The QRSs of 7 days after onset significantly correlated with both infarct size and LVEF; infarct size (CK·g·Eq) = 5.24 QRSs + 8.50 (r = 0.72, p < 0.001), LVEF (%) = − 2.16 QRSs + 59.58 (r = − 0.71, p < 0.001). Patients with exercise tolerance of < 6 minutes had significantly higher QRSs than patients with exercise tolerance of 6 to 12 minutes or >12 minutes (9.0 ± 3.3 versus 4.5 ± 2.4 and 3.6 ± 2.2, p < 0.001, respectively). All patients with QRSs < 6 (24 of 45 patients) achieved exercise tolerance of > 5 minutes, whereas all patients who could not exercise for > 5 minutes (10 of 45 patients) had QRSs > 5. The relation between QRSs and the reasons for termination of LLET showed that patients with fatigue or dyspnea, or both, had significantly higher QRSs (8.7 ± 4.6) than those in target heart rate (5.4 ± 2.2, p < 0.05) and those in completed protocol (3.0 ± 1.7, p < 0.01), whereas patients with chest pain had intermediate QRSs (5.3 ± 2.7). The QRSs was significantly higher in patients with S-T changes during LLET (8.2 ± 4.5 versus 4.7 ± 2.8, p < 0.05). These data suggest that QRSs will be clinically useful not only as a variable correlating with infarct size and LVEF but also as an aid in early identification of exercise performance soon after AMI.