[Quinidine and high-amplification ECG]

High-amplification ECG (HA ECG) is now used routinely to evaluate ventricular tachycardia. The effects of 300 to 600 mg quinidine were determined in 26 heart disease patients with spontaneous and inducible ventricular tachycardia. Programmed ventricular stimulation was performed and an HA ECG recorded (40 Hz high-pass filter) before and under treatment. The stimulation became negative under treatment in nine patients (group I), whereas the 17 others had persistent inducible tachycardia (group II). HA ECG tracings were modified in groups I and II, with a QRS duration increase of 7% and 8%, respectively, and RMS 40 decrease of 37% and 29%, and an LAS increase of 16% and 17%. Furthermore, one of the three group I and four of the seven group II patients who had a normal HA ECG tracing before treatment developed HA ECG abnormalities under treatment. An arrhythmia-inducing effect of the treatment was noted in three group II patients; this effect was not detected by HA ECG. In conclusion, changes in HA ECG tracings were seen during quinidine therapy of patients with ventricular tachycardia, and this effect was independent from the effect of antiarrhythmic agents on induction of the ventricular tachycardia. In addition, abnormalities of high-amplification ECG tracings developed in some patients under quinidine therapy. These data suggest that class I antiarrhythmic agents modify high-amplification ECG tracings and that these modifications fail to predict whether the treatment will prove effective.