Transient leftward QRS axis shift during treadmill exercise testing or percutaneous transluminal coronary angioplasty is a highly specific marker of proximal left anterior descending coronary artery disease.

The efficacy of transient QRS axis shift to the left as a predictor of proximal left anterior descending coronary artery (LAD) disease was assessed. By using receiver operating characteristic curve analysis, we indicated that the difference in modal QRS axis between before and after exercise was useful in detecting proximal LAD disease.