Diagnosis and Treatment
Cardiac Resynchronization Therapy (CRT)
Key Points
����Progression of LV systolic dysfunction to clinical HF is frequently
accompanied by impaired electromechanical coupling, which may
further diminish effective ventricular contractility.
������ The most common disruptions are prolonged AV (first-degree AV block) and
prolonged interventricular conduction, most commonly left bundle-branch block
(LBBB).
������ Prolonged interventricular and intraventricular conduction causes regional
mechanical delay within the left ventricle that can result in reduced ventricular
systolic function, altered myocardial metabolism, functional mitral regurgitation,
and adverse remodeling with ventricular dilatation.
������ Prolongation of the QRS duration occurs in approximately one-third of patients
with advanced HF and has been associated with ventricular electromechanical
delay (���dyssynchrony���).
����QRS duration and dyssynchrony both have been identified as
predictors of worsening HF, sudden cardiac death (SCD), and total
death.
����Modification of ventricular electromechanical delay with multisite
ventricular pacing (commonly called ���biventricular pacing��� or CRT)
can improve ventricular systolic function, reduce metabolic costs,
ameliorate functional mitral regurgitation, and, in some patients,
induce favorable remodeling with reduction of cardiac chamber
dimensions.
Treatment
����CRT is indicated for:
������ patients who have left ventricular ejection fraction (LVEF) ���35%, sinus rhythm,
LBBB with a QRS duration ���150 ms, and NYHA class II, III, or ambulatory IV;
symptoms on guideline-directed medical therapy (GDMT). ���
(I-A for NYHA III/IV; I-B for NYHA II)
����CRT can be useful for patients on GDMT who have LVEF ���35%:
������ sinus rhythm, LBBB with a QRS duration 120-149 ms, and NYHA class II, III, or
ambulatory IV symptoms. (IIa-B)
������ sinus rhythm, a non-LBBB pattern with a QRS duration ���150 ms, and NYHA
class III/ambulatory class IV symptoms. (IIa-A)
������ with AF if: (IIa-B)
������ the patient requires ventricular pacing or otherwise meets CRT criteria and
������ AV nodal ablation or pharmacologic rate control will allow near 100%
ventricular pacing with CRT.
������ and are undergoing new or replacement device placement with anticipated
requirement for significant (>40%) ventricular pacing. (IIa-C)
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