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 atrioventricular (AV) delay, and a significant negative correhtion has been described between tbe critical PQ interval for the appearance of diastolic MR and pulmonary capillary wedge pressure (PCWP) in patients with DDD pacemakers. We report the relationship between the critical PQ interval for the appearance of diastolic MR and the optimal PQ interval in 11 patients (69.1 ± 12.6 years). Cardiac output (CO) and PCWP were measured by Swan-Ganz catheter and transmitral blood flow was recorded by pulsed-Doppler echocardiography. AV delay was prolonged stepwise by 0.025 seconds starting from 0.065 seconds. The pacing rate was fixed at 70 beats/min. CO was highest when the PQ interval was 0.18 ± 0.04 seconds. There was a significant positive correlation between the 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 interval at which CO was the highest was 0.02 ± 0.02 seconds shorter than the critical PQ interval for the appearance of diastolic MR (P < 0.05). When the PQ interval was increased by 0.025 seconds from the critical 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 PQ 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 not exceed the critical PQ interval for the appearance of diastolic MR.