Interatrial Conduction Correlates with Optimal Atrioventricular Timing in Cardiac Resynchronization Therapy Devices

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

BACKGROUND

The interatrial conduction time (IACT) is relevant for atrioventricular delay optimization in cardiac resynchronization therapy (CRT) devices. However, this information cannot be easily used as it requires invasive measurements. We tested whether electrical activation of left atrium (LA) could be detected in CRT devices with left ventricular (LV) sensing and used to estimate IACT.

METHODS

The presence of LA activation on LV channel was evaluated in consecutive patients implanted with CRT and quadripolar LV leads whose sensing was temporarily set in the most proximal polarity (Ring LV4-housing). Estimates of IACT during sinus rhythm and atrial pacing were measured and compared with the values obtained with invasive catheterization of coronary sinus.

RESULTS

Among six patients (50% female; mean age 73.3 ± 4.9 years) included in the analysis, four (66%) had a visible LA signal on the LV channel. The mean IACT measured with device electrograms was 71 ± 8 ms and 133 ± 15 ms during sinus rhythm and atrial pacing, respectively. These values were equivalent to the measurements obtained during invasive catheterization. Both patients without evidence of LA activation had an LV lead with a short total interelectrodes distance (46 mm) resulting in a significant anatomical distance between Ring LV4 and LA.

CONCLUSIONS

In CRT devices with left ventricular sensing, LA signal could be detected and used to estimate IACT especially if long-spaced electrodes are used.

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

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 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.

RESULTS

During 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).

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.

Clinical response with adaptive CRT algorithm compared with CRT with echocardiography-optimized atrioventricular delay: a retrospective analysis of multicentre trials

AIMS

Adaptive cardiac resynchronization therapy (aCRT) is a novel algorithm for CRT pacing that provides automatic ambulatory selection between synchronized left ventricular (LV) or bi-ventricular (BiV) pacing and optimization of atrioventricular (AV) and inter-ventricular (VV) delays based on periodic measurement of intrinsic conduction. We aimed to compare the clinical response between aCRT and standard CRT in historical trials.

METHODS AND RESULTS

The treatment arm of the aCRT trial was compared with a pooled historical control (HC) derived from the CRT arms of four clinical trials (MIRACLE, MIRACLE ICD, PROSPECT, and InSync III Marquis) with respect to the proportion of patients who had an improved clinical composite score (CCS) at the 6-month follow-up. Patients in the HC underwent echocardiography-guided AV optimization after the implant. A propensity score model was used to adjust for 22 potential baseline confounders of the effect of CRT. Patients were stratified into quintiles according to the propensity score and the adjusted absolute treatment effect was obtained by averaging estimates across these quintiles. The propensity score model included 751 patients (aCRT: 266, historical trials: 485). The adjusted absolute difference in percent improved in CCS between the aCRT and HC arms was 11.9% [95% confidence interval (CI): 2.7-19.2%] favouring aCRT. The patients in the aCRT group were significantly more likely to have an improved CCS than the patients in the HC (odds ratio = 1.65, 95% CI: 1.1-2.5).

CONCLUSION

The aCRT algorithm may be associated with additional improvement in clinical response compared with historical CRT with echocardiographic AV optimization.

Discordant electrical and mechanical atrial delays affect intracavitary electrogram-based cardiac resynchronization therapy optimization

AIMS

It has been shown that atrioventricular (AV) delay optimization improves cardiac resynchronization therapy (CRT) response. Recently, an automatic algorithm (QuickOpt™, St Jude Medical), able to quickly identify the individual optimal AV interval, has been developed. The algorithm suggests an AV delay based on atrial intracavitary electrogram (IEGM) duration. We hypothesized that the difference between electrical and mechanical atrial delays could affect the effectiveness of QuickOpt method. The aim of this study was to test this hypothesis in 23 CRT patients who were recipients of St. Jude Medical devices.

METHODS AND RESULTS

Using echocardiography, aortic flow velocity time integral (VTI) was evaluated at baseline, at QuickOpt suggested AV delay and after reducing it by 25 and 50%. Mechanical inter-atrial delay (MIAD) derived from echo/Doppler and electrical inter-atrial delay (EIAD) derived from IEGM were also analysed. Optimal AV delay was identified by the maximal VTI. In 11 patients (Group 1) the maximal VTI was achieved at the AV delay suggested by the algorithm, in 6 patients (Group 2) after a 25% reduction, and in 6 patients (Group 3) after a 50% reduction. While EIAD was similar among the three groups, MIAD was significantly different (P< 0.001). MIAD was longer than EIAD in Group 1 (P= 0.028) and shorter than EIAD in Groups 2 (P= 0.028) and 3. (P< 0.001). Mechanical inter-atrial delay was the only independent predictor of the AV interval associated with the best VTI (R(2) = 0.77; P< 0.001).

CONCLUSION

Our results show that MIAD plays the main role in determining the optimal AV delay, thus caution should be taken when optimizing AV by IEGM-based methods.

Optimization of the atrioventricular delay during cardiac resynchronization therapy using a device for non-invasive measurement of cardiac index at rest and during exercise

AIMS

It is not clear whether cardiac resynchronization therapy (CRT) should only be optimized at rest or whether it is necessary to perform CRT optimization during exercise. Our study aims to answer this question by using an inert gas rebreathing method (Innocor®).

METHODS AND RESULTS

Twenty-seven patients with congestive heart failure and implanted CRT devices were included in the study. The aetiology of the heart failure was ischaemic in nine (33%) patients. Patients had low left ventricular ejection fraction (29 ± 8%) and enlarged LV end-diastolic diameters (63 ± 7 mm). Atrioventricular delay (AVD) was optimized at rest according to cardiac index (CI), measured by inert gas rebreathing (Innocor®). Thereafter, patients performed standardized, steady-state bicycle exercise at 30 W in sitting body position. Three AVDs were tested during exercise in a random sequence: optimized resting AVD (AVD(opt)) according to baseline measurement; AVD(opt) - 30 ms; and AVD(opt) + 30 ms. Cardiac index was measured in each AVD by inert gas rebreathing. Cardiac index increased significantly during exercise. However, neither AVD(opt) shortening nor prolongation during exercise had significant effect on CI (shortening of AVD(opt) - 30 ms was accompanied by a reduction of CI of 4.8%, prolongation of AVD(opt) + 30 ms was accompanied by a reduction of CI of 7.7%).

CONCLUSION

Shortening or lengthening of the AVD during exercise has no impact on CI in CRT patients. On the basis of our results, we conclude that in CRT patients the AVD should be programmed, fixed even during exercise.