CRITICAL PQ INTERVAL FOR THE APPEARANCE OF DIASTOLIC MITRAL REGURGITATION AND OPTIMAL PQ INTERVAL IN PATIENTS IMPLANTED WITH DDD PACEMAKERS

Diastolic mitral regurgitation (MR) may be induced by prolonging atrio ventricular (AV) delay, and a significant negative correlation has bee n described between the critical PQ interval for th-e appearance of di astolic MR and pulmonary capillary wedge pressure (PCWP) in patients w ith DDD pacemakers. We report the relationship between the critical PQ interval for the appearance of diastolic MR and the optimal PQ interv al in 11 patients (69.1 +/- 12.6 years). Cardiac output (CO) and PCWP were measured by Swan-Ganz catheter and transmitral bloodflow uas reco rded by pulsed-Doppler echocardiography. AV delay was prolonged stepwi se by 0.025 seconds starting from 0.065 seconds. The pacing rate was f ixed at 70 beats/min. CO was highest when the PQ interval wets 0.18 +/ - 0.04 seconds. There was a significant positive correlation between t he critical PQ interval for the appearance of diastolic MR and the PQ interval at which CO was the highest (r = 0.91, P < 0.01). The PQ inte rval at which CO was the highest was 0.02 +/- 0.02 seconds shorter tha n the critical PQ interval for the appearance of diastolic MR (P < 0.0 5). When the PQ interval was increased by 0.025 seconds from the criti cal PQ interval for the appearance of diastolic MR, CO decreased from 4.3 +/- 0.6 L/min to 4.1 +/- 0.6 L/min and PCWP increased from 7.5 +/- 6.4 mmHg to 8.5 +/- 7.3 mmHg (P < 0.05). In conclusion, the critical Pa interval for the appearance of diastolic MR may represent the upper limit of the optimal PQ interval and the AV delay should be set to no t exceed the critical PQ interval for the appearance of diastolic MR.