Effects of Atrioventricular Intervals on Right Atrial Monophasic Action Potential Duration during Pacing or Reciprocating Tachycardia

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We evaluated the relationship between changes in the atrioventricular (AV) intervals and right atrial monophasic action potential duration at 90% repolarization (RA-MAPD90) in humans. In 4 patients, RA-MAPD90 was measured during AV reciprocating tachycardia (AVRT, n=2) or AV node reentrant tachycardia (AVNRT, n=2) and atrial or ventricular pacing at similar cycle lengths. In 10 patients, RA-MAPD90 was measured during continuous atrioventricular sequential pacing at AV intervals of 0, 50, 100, 150, 200, 250, 300, 350msec for 90sec at a cycle length of 333-400msec. In patients with AVRT, the RA-MAPD90 during tachycardia was shorter than RA-MAPD90 during RA or RV pacing. In patients with AVNRT, RA-MAPD90 during tachycardia was similar or longer than RA-MAPD90 during RA or RV pacing. As the AV interval was increased from 0msec to 150msec, the peak right atrial pressure decreased from 8-12mm Hg to 2-3mm Hg. RA-MAPD90 decreased to its minimal value at an AV interval of 150msec. The maximal difference in the RA-MAPD90 obtained by changing the AV interval was 22.5±3.0msec. We conclude that 1) a very short AV or VA interval causes an increase in RA-MAPD90 which correlates with an increase in RA pressure, and 2) RA-MAPD90 during supraventricular tachycardia is different from RA-MAPD90 during atrial or ventricular pacing. Thus, a contractionexcitation feedback mechanism may exist in the human atrium.