Hydralazine pharmacodynamics in the dog.

The pharmacodynamics of hydralazine, an arteriolar dilator, were studied in dogs with induced heart failure. The dogs were studied 5 days after heart failure was induced by injecting microspheres into the left circumflex coronary artery. All dogs had a stroke volume index less than 25 ml/beat/m2 of body surface and a left ventricular filling pressure greater than or equal to 16 mm of Hg. Approximately 1 mg of hydralazine/kg of body weight was administered orally each hour until the total systemic resistance index decreased below 1,700 dynes . s X cm-5 X m2. The drug effect was monitored hemodynamically until it dissipated. Hydralazine increased the cardiac index from 3.06 +/- 0.47 (+/- SD) to 6.81 +/- 0.87 L/min/m2 (P less than 0.01), stroke volume index from 20.9 +/- 1.6 to 36.8 +/- 9.3 ml/beat/m2 (P less than 0.01), and heart rate from 146.2 +/- 17.2 to 187.8 +/- 42.8 beats/min (P less than 0.05). It decreased mean arterial pressure from 111.5 +/- 20.4 to 83.8 +/- 4.7 mm of Hg (P less than 0.05) and total systemic resistance index from 2,903 +/- 149 to 992 +/- 83 dynes . s X cm-5 X m2 (P less than 0.001). It did not affect left ventricular filling pressure or contractility. Peak drug effect occurred at 3 to 5 hours after drug administration and duration of effect was 11 to 13 hours. Recurrence of ventricular dysrhythmias occurred in 2 dogs and 1 dog died during a recurrence. Hydralazine improved cardiac performance in the dog with left ventricular failure.