Effect of blood pressure on vascular hemodynamics in acute tachycardia.

Paroxysmal supraventricular tachycardia is accompanied by hypotension, which can affect vascular hemodynamics. Here, we hypothesized that a fall in blood flow as a result of hypotension has a larger effect on hemodynamics in medium-sized peripheral arteries compared with increased pulsatility in rapid pacing. To test this hypothesis, we experimentally and theoretically investigated hemodynamic changes in femoral, carotid, and subclavian arteries at heart rates of 95-170 beats/min after acute pacing. The arterial pressure, blood flow, and other hemodynamic parameters remained statistically unchanged for heart rates ≤ 135 beats/min. Systemic pressure and flow velocities, however, showed an abrupt decrease, resulting in larger alteration of hemodynamic parameters for heart rates ≥ 155 beats/min after pacing (initial period) and then recovered close to baseline after several minutes of pacing (recovery period). During the initial period, the pressure dropped from 88 mmHg (baseline) to 44 mmHg, and the flow velocity decreased to about one-third of baseline at heart rate of 170 beats/min. A hemodynamic analysis showed a velocity profile with a near-wall retrograde flow or a fully reversed flow during the initial period, which vanished at the recovery period. It was concluded that the initial fall of blood flow due to pressure drop led to transient flow reversal and negative wall shear stress because this phenomena was not observed at the recovery period. This study underscores the significant effects of hypotension on vascular hemodynamics, which may have relevance to physiology and chronic pathophysiology in paroxysmal supraventricular tachycardia.