Hemodynamic responses to rapid pacing: a model for tachycardia differentiation.

The hemodynamic responses to rapid atrial and ventricular pacing were examined in 10 closed-chest anesthetized dogs in an attempt to distinguish hemodynamically stable from unstable tachycardias. Pressure monitoring catheters were placed in the femoral artery, right atrium, and right ventricle to measure mean arterial pressure, mean right atrial pressure, and mean right ventricular pressure at baseline heart rate and after rapid high right atrial and right ventricular apex pacing. Pressures recorded during rapid pacing (average of the pressures at 30 and 60 seconds of pacing) at pacing rates of 180, 250, and 280/minute were compared to those recorded initially at baseline heart rates. Rapid right ventricular apex pacing resulted in significant increases in mean right atrial pressure (from 6 +/- 1 mmHg (mean +/- standard error) to 12 +/- 1 mmHg, a 100% increase, P less than 0.001) and mean right ventricular pressure (from 11 +/- 1 mmHg to 16 +/- 1 mmHg, a 45% increase, p less than 0.02) with marked hemodynamic compromise (mean arterial pressure decreased from 85 +/- 6 mmHg to 50 +/- 6 mmHg, a 41% decrease, P less than 0.01). These parameters remained stable (no statistically significant difference from baseline) during high right atrial pacing. In half of the dogs high right atrial pacing at rates greater than or equal to 250 resulted in atrioventricular Wenckebach. Thus, it is concluded that mean right atrial pressure and mean right ventricular pressure may be useful in distinguishing hemodynamically significant tachycardias, and in the future design of antitachycardia devices.