Characterization of impact-induced tachyarrhythmia utilizing propranolol, quinidine and pacing.

Direct impact of the heart on the right ventricle induces transient ventricular tachycardia. Preconditioning the heart with a moderate dose of propranolol (0.4 mg/Kg, IV) did not affect impact-induced tachyarrhthmia although effective beta adrenergic blockage was evident. A high dose of propranolol (1.6 mg/Kg, IV) or a moderate dose of quinidine (3 mg/Kg, IV) prevented impact-induced ventricular tachycardia. High-dose propranolol and quinidine, an agent with no beta blockade properties, share similar local effects on the myocardial cell membrane which was sufficient to prevent the tachyarrhythmia. Pacing of the right ventricular free wall at the impact site resulted in an ECG similar to that observed following impact. Pacing of the subjacent septem, the other possible arrhythmogenic site affected by the impact, resulted in a large aberrant S wave (Lead II) different from the QRS complex during impact-induced tachyarrhythmia. Therefore, impact-induced ventricular tachycardia originates from the impact site by a direct ventricular mechanism.