The effects of ventricular rate and rhythm on the velocity and magnitude of left atrial appendage flow in patients with atrial fibrillation

The objective of the study was to determine if left atrial appendage filling and emptying is affected left ventricular rhythm and rate. 12 patients in atrial fibrillation (AF) with high degree AV block and an indwelling permanent pacemaker (PPM) were studied with the PPM programmed to VVT (triggered) mode. Modification of ventricular rate and rhythm was achieved by triggering the PPM using a programmable device delivering 5-volt monophasic signals transcutaneously. The ventricle was paced at 2 different rates (60 and 120 bpm) in a both regular (R) and an irregular rhythm (IR) simulating AF, and at 150 bpm in a regular rhythm. Doppler trans-esophageal (TEE) recordings of LAA inflow and outflow were performed during each of the 5 sequences, and 10 seconds of recording was analysed off-line for mean velocity of inflow (MLAAI) and outflow (MLAAO) (cm/s). Time-velocity integral (TVI) was determined by tracing Doppler recordings of LAA flow with a digital pen tc give a reading (cm) for magnitude of flow. RESULTS: MLAAI was significantly higher at a ventricular rate of 60 than at a rate of 120 in both R (p=0.004) and IR (p=0.001) rhythms and higher during R compared to IR at a rate of 120 bpm (p=0.05). MLAAI was higher at 60R (p=0.02) and IR (p=0.02) and at 120R (p=0.08) but not 120IR (p=0.4) than at 150 bpm. Similar results were obtained for MLAAO. TVI was higher during R compared to IR at 60 (p=0.02) and 120 (p=0.026) and at 60 compared to 120 during both R and IR. TVI was higher at 60R (p=0.01) and IR (p=0.005) and was higher at 120R (p=0.01) but not 120IR (p=0.185) compared to 150 bpm. CONCLUSIONS: Our results show that LAA flow has a higher velocity and a greater magnitude at slower compared to faster ventricular rates suggesting that ventricular rate control in patients with AF may be important for the prevention of thromboembolism, particularly in those who cannot take warfarin therapy. Furthermore, LAA flow had a higher velocity and a greater magnitude during a regular compared to an irregular ventricular rhythm suggesting that regularisation of the ventricular rhythm in AF may have a similar effect.