Cardiac resynchronization therapy indications

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Sara Zand, M.D.[2] Bhaskar Purushottam, M.D. [3], Hardik Patel, M.D.

Overview

Cardiac resynchronization therapy (CRT) with or without an implantable cardiac defibrillator (ICD) is indicated in patients who have an LVEF less than or equal to 35%, left bundle branch block (LBBB) with a QRS duration greater than or equal to 0.15 seconds, and normal sinus rhythm, for the treatment of NYHA functional Class III or ambulatory Class IV heart failure symptoms in patients whose medical therapy has been optimized.

2021 ESC Guideline for Cardiac Resynchronization Therapy implantation

Abbreviations: AF: Atrial fibrillation; A-V: Atrio-ventricular; CRT: Cardiac resynchronization therapy ; HFrEF: Heart failure with reduced ejection fraction; ICD: Implantable cardioverter-defibrillato; LBBB:Left bundle branch block; LVEF: Left ventricular ejection fraction; NYHA:New York Heart Association; RV: = Right ventricular

Recommendations for cardiac resynchronization therapy implantation in patients with heart failure

(Class I, Level of Evidence A):

❑ CRT is recommended for symptomatic patients with HF in sinus rhythm with a QRS duration ≥150 ms and LBBB QRS morphology and with LVEF ≤35% despite optimal medical therapy in order to improve symptoms and reduce morbidity and mortality ❑ CRT rather than RV pacing is recommended for patients with HFrEF regardless of NYHA class or QRS duration who have an indication for ventricular pacing for high degree AV block in order to reducemorbidity including AF

(Class IIa, Level of Evidence B):

❑ CRT should be considered for symptomatic patients with HF in sinus rhythm with a QRS duration ≥150 ms and non-LBBB QRS morphology and with LVEF ≤35% despite OMT in order to improve symptoms and reduce morbidity and mortality ❑ CRT should be considered for symptomatic patients with HF in sinus rhythm with a QRS duration of130-149 ms and LBBB QRS morphology and with LVEF ≤35% despite optimal medical therapy in order to improve symptoms and reduce morbidity and mortality ❑ Patients with an LVEF ≤35% who have received a conventional pacemaker or an ICD and subsequently develop worsening HF despite optimal medical therapy and who have a significant proportion of RV pacing should be considered for upgrade to CRT

(Class IIb, Level of Evidence B) :

❑ CRT may be considered for symptomatic patients with HF in sinus rhythm with a QRS duration of 130-149 ms and non-LBBB QRS morphology and with LVEF ≤35% despite optimal medical therapy in order to improve symptoms and reduce morbidity and mortality

(Class III, Level of Evidence A) :

❑CRT is not recommended in patients with a QRS duration <130 ms who do not have an indication for pacing due to high degree AV block

The above table adopted from 2021 ESC Guideline

Cardiac resynchronization therapy

• CRT reduces morbidity and mortality.
• CRT improves cardiac function, and enhances quality of life.
• Several characteristics predictors of improvement in morbidity and mortality including the extent of reverse remodelling as the most important mechanisms of action of CRT.
• Patients with HFrEF and ischemic etiology have less improvement in LV function due to myocardial scar tissue, which is less likely to undergo favorable remodelling.
• Women may be more likely to respond to CRT than men, possibly due to smaller body and heart size.
• QRS duration predicts CRT response.
• QRS morphology is related to a beneficial response to CRT.
• Patients with left bundle branch block (LBBB) morphology are more likely to respond favorably to CRT, whereas there is less certainty about patients with non-LBBB morphology.
• Patients with LBBB morphology often have wider QRS durations, and there is a current debate about whether QRS durations or QRS morphology is the

the main predictor of a beneficial response to CRT.

• there is little evidence to suggest that QRS morphology or etiology of disease influence the effect of CRT on morbidity or mortality.
• Implantation of CRT is not recommended if QRS duration is <130 ms.
• If a patient is selected to receive an ICD and is in sinus rhythm, with a LBBB, CRT-D should be considered if the QRS is between 130 and 149 ms and is recommended if QRS is ≥ 150 ms.
• When LVEF is reduced, RV pacing may exacerbate cardiac dyssynchrony.
• This can be prevented by CRT, which might improve patient outcomes.
• CRT rather than RV pacing is recommended for patients with HFrEF regardless of NYHA class who have an indication for ventricular pacing in order to reduce morbidity, although no clear effect on mortality was observed.
• In patients with HFrEF who have received a conventional pacemaker or an ICD and subsequently develop worsening HF with a high proportion of RV pacing, CRT implantation is recommended.
• CRT is superior to RV pacing in patients undergoing atrioventricular (AV) node ablation in AF patients.
• In patients with AF, CRT-D compared with ICD, was not benefit and less than half of patients had >90% biventricular capture.
• CRT in patients with AF may be an option in selected patient with QRS≥ 150 ms, high biventricular pacing.
• When biventricular capture is <98%, it reflects a loss of resynchronization and poor prognosis in CRT.
• Patients with extensive myocardial scar will have less improvement in LV function with CRT.
• Pacing thresholds are higher in scarred myocardium and, if possible, lead placement should avoid such regions.
• Although patients with extensive scarring have an intrinsically worse prognosis, there is little evidence that they obtain less prognostic benefit from CRT.
• Optimization of AV intervals or interventricular delay intervals (VV intervals) after implantation by using echo- or electrocardiographic criteria or BP response may be considered for patients who have had no response to CRT.