Cardiac Resynchronization Therapy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Associate Editor: Cafer Zorkun, M.D., Ph.D. [2] Assistant Editor: Atif Mohammad, MD

Introduction

Cardiac resynchronization therapy is a relatively new mode of therapeutic modality currently being used particularly in patients with advanced heart failure.Bi-ventricular pacing or pacing one of the ventricles with bundle branch block is referred to as Cardiac Resynchronization Therapy.

Currently CRT has been approved in patients with advanced HF patients benefit from simultaneous pacing of both ventricles (biventricular or BiV pacing) or of one ventricle in patients with bundle branch block. This approach is referred to as cardiac resynchronization therapy (CRT) . CRT can be achieved with a device designed only for pacing or can be incorporated into a combination device with an ICD.

Cardiac Resynchronization therapy has been approved for patients with advanced heart failure NYHA class III,IIV or patients with LVEF <35% and with QRS delay >120 ms.It has gain FDA approval for patients with NYHA class I OR II heart failure in the setting of QRS delay.

Mechanism of Benefit

CRT in Heart Failure

CRT has been known to benefit patients with left ventricular dyssynchrony.The mechanism is till unclear but it is known to improve contractile performance of cardiac chambers and hence result in reverse remodeling improving functional capacity and decreasing clinical outcomes of mortality and repeat hospitalizations.Basically, CRT causes improved cardiac myocyte depolarization as a result of cardiac resynchronization which improves cardiac systolic function causing contraction of the left ventricle and thus reducing wall stress and mitral regurgitation.This also improves ventricular remodeling .

Improved contractility of LV in patients with HF associated with IVCD or LBBB is known to reduce myocardial energy demands and oxygen consumption.

CRT has shown to cause reverse ventricular remodeling.A study conducted in Hong Kong showed long term clinical improvement in patients treated with CRT. But it is still not clear whether,clinical improvement and ventricular remodeling correlate with each other or ventricular remodeling is necessary for reduction in clinical signs and symptoms.

CRT in Afib

Cardiac resynchronization Therapy is mostly used in Chronic Afib in patients with a node ablation indication.CRT has shown to increases peak oxygen consumption and increased exercise duration as compared to standard RV pacing.It has shown to reduce atrial size and activation along with reduction in degrees of mitral regurgitation.It has also known to improve LVEF in patients with chronic Afib.
It is still not clearly known to benefit in patients in Afib with heart failure.
Observational studies have shown significant improvement when CRT is combined with AV node ablation.But there is not enough data to show benefits with other modes of therapy like pulmonary vein isolation.

Major Society Guidelines

Therefore, common indications for CRT implantation according to the recent guidelines of the American Heart Association/American College of Cardiology/Heart Rhythm Society (AHA/ACC/HRS),HFSA,

1. The 2008 ACC/AHA/HRS guidelines for device-based therapy of cardiac rhythm abnormalities included recommendations for both CRT devices and ICD implantation [44]. The guidelines did not include specific recommendations regarding when a device with both capabilities should be used.
2. The 2010 Heart Failure Society of America (HFSA) practice guidelines recommend that concomitant ICD placement be considered in NYHA class III or IV patients undergoing implantation of a biventricular pacing device according to HFSA criteria

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