His bundle pacing to avoid electrical dyssynchrony with traditional right ventricular pacing: Importance of heart size

Optimizing conduction system pacing lead placement utilizing the image overlay technique

The His-bundle has several locations from which conduction system pacing can be achieved. Some locations offer better sensing, thresholds and paced QRS durations. Existing techniques to aid repositioning of an already deployed, but sub-optimally placed lead, include either simple memory of the initial lead position combined with its observation on an x-ray review screen or utilizing an additional vascular access and pacing lead with the first lead serving as a real-time marker (Two-lead technique). We describe a novel, readily available, cost-efficient, imaging-based approach to assist in the re-positioning of a pacing lead for His-bundle pacing (the Image Overlay Technique).

His-Optimized and Left Bundle Branch-Optimized Cardiac Resynchronization Therapy: In Control of Fusion Pacing

Fusion pacing, which exploits conduction via the intrinsic His-Purkinje system, forms the basis of recent cardiac resynchronization therapy (CRT) optimization algorithms. However, settings need to be constantly adjusted to accommodate for changes in AV conduction, and the algorithms are not always available (eg, depending on the device, in case of AV block or with atrial fibrillation). His-optimized cardiac resynchronization therapy (HOT-CRT), and left-bundle branch optimized cardiac resynchronization therapy (LOT-CRT) which combines conduction system pacing with ventricular fusion pacing, provide constant fusion with ventricular activation (irrespective of intrinsic AV conduction). These modalities provide promising treatment strategies for patients with heart failure, especially in those with chronic atrial fibrillation who require CRT (in whom the atrial port is usually plugged and can be used to connect the conduction system pacing lead).

Structural heart disease, not the right ventricular pacing site, determines the QRS duration during right ventricular pacing

Right ventricular (RV) pacing causes changes in the heart's electrical and mechanical activation patterns. The QRS duration is a useful surrogate marker of electrical dyssynchrony; a longer QRS duration during RV pacing indicates poor prognosis. However, the mechanisms underlying a longer QRS duration during RV pacing remain unclear; hence, we investigated factors predicting QRS prolongation during RV pacing. We enrolled 211 patients who underwent catheter ablation for supraventricular tachyarrhythmia and showed no bundle branch block. Three-dimensional mapping for the QRS duration during RV pacing from the RV outflow to RV apex was performed, and differences in the QRS duration were analyzed. The predisposing factors causing QRS > 160 ms during RV apical pacing were also analyzed. The QRS durations at baseline and during RV pacing from the RV outflow and at the RV apex were 85.0 ± 7.5 ms, 163.7 ± 17.1 ms, and 156.2 ± 16.1 ms, respectively. With respect to the QRS duration, there was a significant correlation between RV outflow and RV apical pacing (r = 0.658, p < 0.001). Difference in the QRS duration between the RV outflow and RV apex in each patient was only 12.5 ± 10.4 ms. Logistic multivariable regression analysis identified baseline QRS duration [odds ratio (OR) 1.24, 95% confidence interval (CI) 1.15-1.33, p < 0.01], interventricular septum thickness (OR 1.20, 95% CI 1.02-1.40, p = 0.025), left atrial diameter (OR 1.08, 95% CI 1.01-1.16, p = 0.024), and E/e' (OR 1.23, 95% CI 1.12-1.35, p < 0.01) as significant predictors of QRS prolongation during RV apical pacing. The QRS duration during RV pacing largely depends not on the pacing site, but on the underlying structural heart diseases.

His-Optimized Cardiac Resynchronization Therapy With Ventricular Fusion Pacing for Electrical Resynchronization in Heart Failure

OBJECTIVES

This study sought to evaluate the effectiveness of His-optimized cardiac resynchronization therapy (HOT-CRT) for reducing left ventricular activation time (LVAT) compared to His bundle pacing (HBP) and biventricular (BiV) pacing (including multipoint pacing [MPP]), using electrocardiographic (ECG) imaging.

BACKGROUND

HBP may correct bundle branch block (BBB) and has shown encouraging results for providing CRT. However, HBP does not correct BBB in all patients and may be combined with univentricular or BiV fusion pacing to deliver HOT-CRT to maximize resynchronization.

METHODS

Nineteen patients with a standard indication for CRT, implanted with HBP without correction of BBB and BiV (n = 14) or right ventricular (n = 5) leads, were prospectively enrolled. Patients underwent ECG imaging while pacing in different configurations using different LV electrodes and at different HBP ventricular pacing (VP) delays. The primary endpoint was reduction in LVAT with HOT-CRT, and the secondary endpoints included various other dys-synchrony measurements including right ventricular activation time (RVAT).

RESULTS

Compared to HBP, HOT-CRT reduced LVAT by 21% (-17 ms [95% confidence interval [CI]: -25 to -9 ms]; p < 0.001) and outperformed BiV by 24% (-22 ms [95% CI: -33 to -10 ms]; p = 0.002) and MPP by 13% (-11 ms [95% CI: -21 to -1 ms]; p = 0.035). Relative to HBP, HOT-CRT also reduced RVAT by 7% (-5 ms [95% CI: -9 to -1 ms; p = 0.035) in patients with right BBB, whereas RVAT was increased by BiV. The other electrical dyssynchrony measurements also improved with HOT-CRT.

CONCLUSIONS

HOT-CRT acutely improves ventricular electrical synchrony beyond BiV and MPP. The impact of this finding needs to be evaluated further in studies with clinical follow-up. (Electrical Resynchronization and Acute Hemodynamic Effects of Direct His Bundle Pacing Compared to Biventricular Pacing; NCT03452462).