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Relation of QRS Duration to Response to Cardiac Resynchronization Therapy in Patients With Left Bundle Branch Block
Biagio Sassone1, Matteo Bertini2, Matteo Beltrami3
1Department of Cardiology, SS.ma Annunziata Hospital, Azienda Unità Sanitaria Locale Ferrara, Cento, Ferrara, Italy; Department of Cardiology, Delta Hospital, Azienda Unità Sanitaria Locale Ferrara, Lagosanto, Ferrara, Italy.
Insights
In patients with left bundle branch block (LBBB), a wider QRS duration with less left ventricular dyssynchrony (LVdys) may predict a poorer response to cardiac resynchronization therapy (CRT), especially in nonischemic cardiomyopathy.
Area of Science:
- Cardiology
- Medical Imaging
- Electrophysiology
Background:
- Left ventricular dyssynchrony (LVdys) is crucial for successful cardiac resynchronization therapy (CRT).
- Left bundle branch block (LBBB) often indicates LVdys, but not all LBBB patients benefit from CRT.
- Predicting CRT response in LBBB patients remains a clinical challenge.
Purpose of the Study:
- To investigate the relationship between QRS duration and LVdys in LBBB patients undergoing CRT.
- To identify predictors of non-response to CRT in this patient population.
- To explore differences in this relationship based on the etiology of cardiomyopathy.
Main Methods:
- Retrospective study of 165 LBBB patients who received CRT.
- Responders defined by a ≥15% reduction in LV end-systolic volume at 6 months.
- LVdys assessed by the delay in peak systolic velocities between septum and lateral wall using tissue Doppler imaging.
Main Results:
- Non-responders (39%) had significantly larger QRS duration (172 ± 24 ms vs 160 ± 16 ms) and lower LVdys (46 ± 42 ms vs 72 ± 31 ms) compared to responders (61%).
- A QRS duration to LVdys ratio (QRS/LVdys) >3 predicted non-responsiveness with 66% sensitivity and 80% specificity.
- In nonischemic cardiomyopathy, increased QRS duration correlated inversely with LVdys (p=0.006).
Conclusions:
- In LBBB patients with nonischemic cardiomyopathy and marked QRS widening, reduced LVdys may lead to lower CRT response rates.
- The QRS/LVdys ratio is a potential predictor of CRT non-responsiveness.
- Further research is needed to optimize CRT selection in LBBB patients.
Abstract:
Left ventricular (LV) dyssynchrony (LVdys) is a necessary condition for successful cardiac resynchronization therapy (CRT). Despite left bundle branch block (LBBB) representing a reliable surrogate of LVdys, not all LBBB patients will respond to CRT. Our aim was to investigate the relation between QRS duration and LVdys in patients with LBBB who underwent CRT. We retrospectively studied 165 patients with LBBB who underwent CRT implantation according to the current guidelines. A 6-month reduction of LV end-systolic volume ≥15% identified responders to CRT. Baseline LVdys was defined as the delay between peak systolic velocities of the interventricular septum and lateral wall assessed by color-coded tissue Doppler imaging. Baseline characteristics of responders (61%) and nonresponders (39%) were comparable except for larger QRS complex (172 ± 24 vs 160 ± 16 ms, p <0.001) and lower degree of LVdys (46 ± 42 vs 72 ± 31 ms, p <0.001) in nonresponders. Receiver-operating characteristic curve analysis demonstrated that an optimal cut-off value of 3 for the ratio of QRS duration and LVdys (QRS/LVdys) yielded a sensitivity of 66% and specificity of 80% to predict nonresponsiveness to CRT; QRS/LVdys >3 remained an independent predictor at multivariate analysis. In patients with nonischemic origin of cardiomyopathy, the linear regression analysis documented a significant inverse relation between QRS duration and LVdys, as dyssynchrony progressively decreased as QRS widening increased (p = 0.006). This was not evident in patients with ischemic origin. In conclusion, in LBBB patients with nonischemic origin and marked QRS widening, the absence of LVdys may account for a lower response to CRT compared with patients with intermediate QRS widening.