Left ventricular paced activation in cardiac resynchronization therapy patients with left bundle branch block and relationship to its electrical substrate

Figures

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  Figure 1. Electrical relationships key to cardiac resynchronization: analytical plan. AVD = atrioventricular delay; LV = left ventricle; RV = right ventricle.

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  Figure 2. Intrinsic conduction in left bundle branch block. A: Intrinsic left ventricular electrical delay (qLV) varies little between the distal and proximal bipoles of quadripolar leads in both ischemic and nonischemic patients. B: A similar trend is seen in RV sense to LV sense time (RVs–LVs), an automated device-based surrogate of intrinsic LV electrical delay. However, this measurement is significantly less than qLV (32% ± 15%). LV = left ventricle; RV = right ventricle.

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  Figure 3. Characteristics of intrinsic conduction gradients: effect of pacing. A: Representative tracings of RV and LV intrinsic electrical delay (qLV) from the electrophysiology lab recording system. Intervals were measured from the onset of the surface QRS to the RV (qRV), LV distal (D1-M2), and LV proximal (M3-P4) bipoles. B: Gradients, defined as ≥20 ms difference between qLV at the distal and proximal LV bipoles, are thought to be confined to patients with ischemic disease yet are present in a similar proportion in nonischemic patients. C: Resolution (or exacerbation) of intrinsic conduction gradients during LV (left) or RV (right) pacing. Each line represents 1 patient with nonischemic (solid) or ischemic (dashed) etiology. Gradients are highlighted in gray.D: In both ischemic and nonischemic patients, a majority of gradients are functional, as they are resolved by changing the direction of ventricular activation with RV or LV pacing. Exacerbation of existing gradients was rare. LV = left ventricle; RV = right ventricle.

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  Figure 4. Characteristics of right ventricular and left ventricular pacing in left bundle branch block. A: RV paced to LV sense time: schematic representation of the pacing protocol (left) and representative tracings from the electrophysiology lab recording system of time from the pacing artifact of the surface QRS during RV pacing (middle). LV electrical activation times during RV pacing (right) are significantly longer when measured at the proximal vs distal LV bipole regardless of etiology and 9% longer in patients with ischemic cardiomyopathy. B: LV paced to RV sense time: schematic representation of the pacing protocol (left) and representative tracings from the electrophysiology lab recording system of time from the pacing artifact of the surface QRS during LV pacing (middle). LV electrical activation times during LV pacing (right) with similar differences in conduction time are observed during distal (or proximal) LV pacing measured to the RV bipole. LV paced to RV sense times were significantly longer than the RV paced to LV sense times in all but the proximal bipole of nonischemic patients. C: Difference in paced conduction time [(LV pace to RV sense) – (RV pace to LV sense)] in…

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  Figure 5. Relationship between intrinsic LV electrical delay (qLV) and LV paced conduction in patients with left bundle branch block (LBBB). There is poor corelation between maximum intrinsic electrical delay (qLV) and LV pace to RV sense time (LVp–RVs) from the same bipole in both ischemic (A) ad nonischemic patients (B) with LBBB. This suggests that LV-paced conduction is largely independent of intrinsic electrical delay and electrical substrate and should be evaluated independently of qLV. LV = left ventricle; RV = right ventricle.

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  Figure 6. Left ventricular intraventricular conduction time: intrinsic and paced. A: Schematic representation of conduction time measurements during intrinsic conduction (left) and pacing from the distal LV bipole (middle) and the proximal LV bipole (right). B, C: Representative tracings from the electrophysiology lab recording system showing the intraventricular conduction time during intrinsic conduction (left) between the proximal and distal LV bipoles (ΔqLV), and paced conduction time measured from the pacing artifact on the surface QRS during LV-only pacing from the distal bipole to the local intracardiac electrogram on the proximal LV bipole (middle). Pacing was then reversed, and the interval between the proximal and distal LV bipoles was measured (left). Two different patients show variability in intraventricular paced conduction times: one short (45 ms) (B) and one long (95 ms) (C). D: LV epicardial paced conduction times are significantly longer than during intrinsic conduction (left) and are unrelated to pre-existing intrinsic conduction gradients (right). LV = left ventricle.

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  Supplemental Figure 1.