Value of the electrocardiographic stress test by atrial pacing in the healing stages of experimental myocardial infarction.

To check up the value of atrial pacing (AP) in estimating the degree of healing in myocardial necrosis, an ECG study was carried out in 20 dogs with experimental myocardial infarction induced by ligation of the left descending coronary artery. The main ECG changes recorded after ligation i.e., Q waves in 14 animals (73%), S-T segment elevation in 14 (74%) and decrease of QRS voltage in 12 (63%), disappeared within a 7-day interval. Anesthesia with Nembutal 56--57 days after ligation and before AP application induced the occurrence of Q waves in 6 animals, S-T segment depression in 18 and T wave inversion in 12. AP during 20 minutes, at a heart rate of 200 beats/min, produced the appearance or the increase of S-T segment depression in 14 animals and T wave inversion in 12. These findings support the assumption that the AP stress test can be used for the evaluation of the necrosis degree in the healing stages of experimental myocardial infarction, but a correct interpretation of the ECG changes induced by AP should also take into account the previous abnormalities due to anesthesia.