| Abstrakt: |
Background: Controversy 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.Methods: Twenty 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 atriallypaced rates: 5, 25, and 45 beats/min above rest, denoted as A paced,r + 5, A paced, r + 25, and A paced,r + 45, respectively. Left atrial myocardial motion and transmitral flow were timed echocardiographically.Results: During atrial sensing, raising heart rate shortened optimal AV delay by 25 ± 6ms (P < 0.001). During atrial pacing, raising heart rate from A paced,r+5 to A paced,r+25 shortened it by 16±6 ms; A paced,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).Conclusions: Hemodynamic 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. [ABSTRACT FROM AUTHOR] |
