Distinct impacts of heart rate and right atrial‐pacing on left atrial mechanical activation and optimal AV delay in CRT

Abstract

BackgroundControversy exists regarding how atrial activation mode and heart rate affect optimal atrioventricular (AV) delay in cardiac resynchronization therapy. We studied these questions using high‐reproducibility hemodynamic and echocardiographic measurements.MethodsTwenty patients were hemodynamically optimized using noninvasive beat‐to‐beat blood pressure at rest (62 ± 11 beats/min), during exercise (80 ± 6 beats/min), and at three atrially paced rates: 5, 25, and 45 beats/min above rest, denoted as Apaced,r+5, Apaced,r+25, and Apaced,r+45, respectively. Left atrial myocardial motion and transmitral flow were timed echocardiographically.ResultsDuring atrial sensing, raising heart rate shortened optimal AV delay by 25 ± 6 ms (P < 0.001). During atrial pacing, raising heart rate from Apaced,r+5 to Apaced,r+25 shortened it by 16 ± 6 ms; Apaced,r+45 shortened it 17 ± 6 ms further (P < 0.001).In comparison to atrial‐sensed activation, atrial pacing lengthened optimal AV delay by 76 ± 6 ms (P < 0.0001) at rest, and at ∼20 beats/min faster, by 85 ± 7 ms (P < 0.0001), 9 ± 4 ms more (P = 0.017). Mechanically, atrial pacing delayed left atrial contraction by 63 ± 5 ms at rest and by 73 ± 5 ms (i.e., by 10 ± 5 ms more, P < 0.05) at ∼20 beats/min faster.Raising atrial rate by exercise advanced left atrial contraction by 7 ± 2 ms (P = 0.001). Raising it by atrial pacing did not (P = 0.2).ConclusionsHemodynamic optimal AV delay shortens with elevation of heart rate. It lengthens on switching from atrial‐sensed to atrial‐paced at the same rate, and echocardiography shows this sensed‐paced difference in optima results from a sensed‐paced difference in atrial electromechanical delay.The reason for the widening of the sensed‐paced difference in AV optimum may be physiological stimuli (e.g., adrenergic drive) advancing left atrial contraction during exercise but not with fast atrial pacing.

Optimization of the atrioventricular delay in conduction system pacing

“…The RASL is a measure of the delay with which the device senses the atrial depolarization front through the atrial lead, compared to the beginning of its propagation from the sinus node (P wave onset on surface ECG). 21 , 28 In this way, an increased RASL could stand for an increased distance from the sinus node to the RA appendage and thus the RASL should be interpreted as a surrogate of RA enlargement. This delay is not negligible, as in our population it was on average 40 ms, therefore it should be taken into account for sAVD programming.…”

“…In all our patients the RA lead was placed in the appendage and all patients were in SR. The RASL is a measure of the delay with which the device senses the atrial depolarization front through the atrial lead, compared to the beginning of its propagation from the sinus node (P wave onset on surface ECG) 21 , 28 …”

“…In selective and nonselective HBP patients, EP-guided sAVD was obtained by subtracting from 150 ms the right atrial (RA) sensing latency (RASL) time and the His-ventricular (HV) interval. RASL was defined as the time from the onset of the P wave on the surface ECG to the time of local RA electrogram (EGM) as recorded and sensed by the atrial lead during SR. 21 This time was measured, by means of electronic callipers, on a simultaneous recording of the RA EGM and of surface ECG performed by the programmer during device interrogation, with the programmer's surface ECG leads connected to the patient. The HV interval was defined as the time interval between the onset of the HB potential and the onset of the QRS complex on the surface ECG: the interval was measured during the implantation procedure (Figure 2, panel A and C).…”

Interatrial conduction time from electrograms of cardiac resynchronization therapy devices with left ventricular sensing

“…Recently, Kyriacou et al also studied the effect of heart rate on timing of left atrial contraction showing that elevating heart rate by exercise shorted IACT; thus, causing an early LA activation 9 . On the other hand, this phenomenon was not observed whether heart rate was artificially increased by atrial pacing.…”

“…Recently, Kyriacou et al also studied the effect of heart rate on timing of left atrial contraction showing that elevating heart rate by exercise shorted IACT; thus, causing an early LA activation. 9 On the other hand, this phenomenon was not observed whether heart rate was artificially increased by atrial pacing. These findings suggested that the optimization of dynamic AV delay in CRT device should be set differently according to the atrial rhythm as the sensed-paced discrepancy could tend to increase at higher heart rates.…”