Production of increased right-to-left shunting by rapid heart rates in patients with tetralogy of Fallot.

A patient with tetralogy of Fallot who developed cyanosis and tachypnea during spontaneous attacks of paroxysmal atrial tachycardia had an increase in right-to-left shunting with a fall in arterial oxygen saturation from 96 to 43%. Duplication of the fast heart rate by atropine and atrial pacing reproduced these hemodynamic changes, while slowing the rate with propranolol reversed this effect. Subsequently, six patients with mild tetralogy of Fallot underwent rapid atrial pacing during cardiac catheterization. This primary increase in heart rate resulted in a fall in systemic oxygen saturation, an increase in percent right-to-left shunt, and an increase in the right ventricular outflow pressure gradient. These data suggest that further narrowing of the right ventricular infundibulum may occur during tachycardia. This experience indicates that paroxysmal atrial tachycardia should be added to the conditions that can cause increased cyanosis in some patients with tetralogy of Fallot. Other tachycardias may also augment right-to-left shunting.