Last updated on November 2017

CRT IMPLANT STRATEGY USING THE LONGEST ELECTRICAL DELAY FOR NON-LEFT BUNDLE BRANCH BLOCK PATIENTS (ENHANCE CRT)


Brief description of study

CRT IMPLANT STRATEGY USING THE LONGEST ELECTRICAL DELAY FOR NON-LEFT BUNDLE BRANCH BLOCK PATIENTS (ENHANCE CRT)

Detailed Study Description

Numerous clinical studies have evaluated the benefits of biventricular pacing compared to optimal medical therapy1,2. However, some patients, who have undergone a successful implantation of a biventricular pacing device, do not have a measurable improvement in cardiac performance or symptoms3. Such patients are generally considered to be CRT non-responders. Clinical studies have suggested that there may be many factors that contribute to the non-responder rate and there is a considerable degree of interpatient and intrapatient variability. Some of these factors include the absence of significant areas of dyssynchrony prior to device implantation, etiology of heart disease (ischemic versus nonischemic), coronary sinus lead position, and inadequate device programming based on patient-specific physiology4. An ongoing area of important investigation for CRT is to reduce the non-responder rate.

Historically, CRT response in RBBB patients has not been as positive as it has been for LBBB patients.5 Early studies assessing the impact of LV lead position on the non-responder rate have suggested that the ideal lead position is in the lateral or posterolateral wall.6,7 The lateral or posterolateral wall lead position has worked well in LBBB patients.8 The same anatomical implant strategy may or may not be effective for RBBB patients as evidenced by the high nonresponder rate.

The anterior vein may be an alternative LV lead location for nonresponders. Research has shown that the anterior vein has not been a popular choice for LV lead placement in the past.9 The lack of use may be due to its proximity to the right ventricle. Physicians have tried to circumvent this issue by placing the lead as basal as possible in the anterior vein to stimulate the left ventricle and promote CRT. Research has shown that if the LV lead is successfully placed in the middle or basal portion of the anterior vein, then there isn’t an increase in heart failure or death.10 The downfall of this strategy is that when the distal end of the lead is placed in the basal portion of the anterior vein, then the LV lead is not anchored securely in the anterior vein. The usefulness of the anterior vein in CRT can be evaluated with the four electrodes that are available on the Quartet LV lead. The physician can program the basal electrode of the Quartet LV lead while securely anchoring the distal portion of the LV lead in the apex of the anterior vein.

QRS widening and morphology changes are associated with ventricular dysynchrony. A substudy of the MADIT-CRT trial investigated whether LBBB and non-LBBB patients with a wide QRS (> 130ms) benefit from CRT. Patients with LBBB, wide QRS and CRT had slower heart failure progression and decreased risk of ventricular tachyarrhythmias. Non-LBBB patients with wide QRS did not experience any clinical benefit from CRT.11 A substudy of the CARE-HF trial examined whether electrocardiographic characteristics at baseline can predict long term health outcomes. While LBBB and RBBB were not independent predictors of mortality and unplanned hospitalizations, the results revealed that the presence of RBBB is associated with higher mortality and unplanned hospitalization than the presence of LBBB12. The authors note that the poor outcome of the RBBB patients could be due to non-response to CRT.

Clinical Study Identifier: TX8485

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Feather Wafford

Baptist Health Clinical Research Center & Lexington Cardiac Research Foundation
Lexington, KY USA
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