Cardiac resynchronisation therapy

Last revised by Henry Knipe on 5 May 2023

Cardiac resynchronisation therapy (CRT) refers to simultaneous biventricular or multisite pacing of the heart with a specialized biventricular cardiac pacemaker (CRT-P) with or without an implantable cardioverter-defibrillator (CRT-D) and is a treatment option in moderate to severe heart failure.

Cardiac resynchronisation therapy has been performed since the 1990s and constituted a big advancement in the therapy of patients with heart failure with the first biventricular pacing device implanted in 1994 1.

The typical indication of cardiac resynchronisation therapy is the improvement of cardiac hemodynamics and symptoms in heart failure with left ventricular dysfunction to prevent hospitalization and reduce mortality, especially in the setting of left bundle branch block (LBBB) and/or cardiac dyssynchrony 1-5. According to the European Society of Cardiology (ESC Guidelines 2021), this includes symptomatic patients (NYHA class II, III and IV) with heart failure with reduced ejection fraction (LVEF <35%) and the following 1:

  • LBBB morphology and QRS ≥150 ms (I)

  • LBBB morphology and QRS 130-149 ms (IIa)

  • non-LBBB morphology and QRS ≥150 ms (IIa)

Clinical characteristics that favor a biventricular pacemaker over a defibrillator with cardiac resynchronisation therapy include 1:

  • non-ischemic cardiomyopathy

  • shorter life expectancy and major comorbidities

  • poor renal function

  • patient preference

Contraindications to cardiac resynchronization therapy are heart failure with QRS <130 ms and no indication for right ventricular pacing, further relative contraindications include the following:

  • right bundle branch block

  • non-left bundle branch block patterns with a QRS <150 ms

  • extensive comorbidities with severely limited survival (e.g. < 1 year)

Cardiac resynchronisation therapy comprises the implantation of a biventricular pacing device either a pacemaker or implantable cardioverter-defibrillator with two or more bipolar or multipolar pacing leads. The procedure includes the following steps:

  • venous access via axillary, cephalic or subclavian veins

  • insertion and placement of the right ventricular lead

  • insertion and placement of the left ventricular lead into the coronary sinus and most suitable lateral or posterolateral cardiac veins

  • insertion of the atrial lead

  • device placement into an infraclavicular subcutaneous pocket of the left or right chest wall

Complications of cardiac resynchronisation device placement include the following 1,4:

A chest x-ray will show a biventricular cardiac conduction device with leads in the right ventricle and left ventricle and generally one in the right atrium.

Echocardiography can be used for the evaluation of mechanical dyssynchrony and in the prediction of response to cardiac resynchronisation therapy as well as for follow-up and to assess reverse remodeling 5,6.

Cardiac CT might be conducted for the evaluation of coronary sinus anatomy and in the setting of complications.

Cardiac MRI can be of use in the preprocedural evaluation of the heart and the assessment of the following 5:

The latter might be of use in the selection of a pacemaker versus a defibrillator 7.

Preprocedural imaging evaluation might include the following 1:

The radiology report after device placement should include a description of the biventricular pacemaker:

  • cardiac lead position (right ventricle, coronary sinus, right atrium near the right atrial appendage)

  • complications such as pericardial effusion and pneumothorax

Cardiac resynchronisation therapy combined with optimal medical therapy has been shown not only to improve symptoms, left ventricular ejection fraction and quality of life but also to promote reverse remodeling and to reduce hospitalizations morbidity and mortality in patients with heart failure 1-4,8.

Factors predicting response and improved outcome to cardiac resynchronization therapy include 2-5,9:

Factors that are less likely associated with a positive or suboptimal response include 2,3:

  • non-left bundle branch block QRS morphology such as right bundle branch block

  • ischemic cardiomyopathy or extensive myocardial scar

  • suboptimal medical therapy

  • suboptimal lead position

  • moderate to severe secondary mitral regurgitation

  • right ventricular systolic dysfunction

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