Pacing For Patients With Congestive Heart
Failure And Dilated Cardiomyopathy

Satish Goel, M.D., FACC

 

Introduction

With the developments that improve survival in patients with left ventricular dysfunction (medical therapy with ace inhibitors, b blockers, Coronary artery bypass surgery and automatic implantable cardioverter defibrillators) congestive heart failure (CHF) is a problem being seen with increased frequency by the practicing cardiologist. It is estimated that there are currently more than 2 million people with heart failure due to left ventricular dysfunction in the United States. The annual incidence of heart failure in the United States is 400,000 new cases each year and will undoubtedly increase further with a population that is gradually aging. In addition mortality in the setting of heart failure has remained disproportionately high, with many of these deaths being sudden and presumed arrhythmic.

Background

Epidemiological studies suggest that 20-30% of the patients diagnosed with symptomatic CHF have intraventricular conduction disorders characterized by a discordant contraction pattern and wide QRS. Presence of a left bundle branch block may result in delayed contraction of the lateral wall of the lt. ventricle (LV). This asynchronous contraction of the LV may result in further deterioration of systolic function and increased myocardial oxygen demand. Bi-ventricular pacing attempts to improve this condition by resynchronizing the contraction of the LV.

Technique

Biventricular pacing involves placement of an additional pacing lead on the epicardial surface of the LV, besides a conventional pacing in the Rt. Ventricle. This is performed in an effort to resynchronize the contraction of the LV. Placing a lead in the cavity of the LV can result in complications due to thromboembolization, as thrombi frequently form on the surface of these leads. Therefore the LV lead is placed epicardially on the surface of the LV. In the initial experience, the LV leads were placed via a thoracotomy or through a throracoscopy. Understandably this procedure can add significantly to the morbidity and mortality of these already sick patients. Subsequently a technique was developed where the pacing wire can be positioned on the surface of the LV transvenously. The venous return form the myocardium consists of multiple veins that are located on the surface of the heart which join to form the Coronary Sinus (CS). The CS then drains into the right atrium. It is possible to cannulate and CS from the right atrium and retrogradely place a pacing lead which is the positioned into one of its branches on the surface of the LV.

 

Results Of Clinical Studies Of BiVentricular Pacing in Heart Failure

There have been several acute hemodynamic and clinical follow up studies which have generally shown advantageous results of biventricular pacing. 3 clinical studies are worth mentioning here :

The MIRACLE (Multicenter InSync Randomized Clinical Evaluation) Trial

NYHA functional class III or IV, LVEF <35% on stable heart failure pharmacological regimen.

Randomization protocol is shown below.

Results

Met primary endpoints

  • QOL improvement
  • NYHA classification improvement
  • 6-min walk improvement

Met secondary endpoints

  • LVEDD decrease was significant
  • Increase in ejection fraction was significant
  • Significant decrease in hospital days

Based On the above study, the Food and Drugs Administration (FDA) approved the biventricular pacing device for the following indication:

  • Moderate to Severe Heart Failure (NYHA Class III/IV)
  • QRS ³ 130 ms
  • LV Ejection Fraction £ 35%
  • Stable, Optimal Medical Therapy

Path CHF study

Single Blinded randomized crossover, controlled trial for patients with moderate to severe cardiomyopathy and bundle branch block.

53 patients included in Europe over 7 centers.

Results showed 28% improvement in LV contraction ( dP/dT), 16% increase in pulse pressure, prolongation of 6min walk test by 60 meters, improvement in peal Vo2 by 23% and improvement in Quality of life and NYHA classification.

The MUSTIC ( Multi-Site Stimulation In Cardiomyopathy)Trial

Patients with advanced dilated cardiomyopathy with QRS duration >150ms received Biventricular pacemakers and were then randomized to VVI pacing at 40 BPM and VDD biventricular pacing . Results showed 23% improvement in 6 min walk distance and 32% increase in quality of life.

Ongoing Trials

More clinical trials are ongoing to look at improvement in various clinical parameters and possible mortality benefit from biventricular pacing. To this date there is no data to suggest any mortality benefit from biventricular pacing.

The COMPANION trial is a muticenter randomized North American trial where patients with dilated cardiomyopathy and intraventricular conduction delay are randomized to 1) bi-ventricular pacing, 2) bi-ventricular pacing with an AICD and 3) no device (control).

The end points include mortality, number of hospitalizations, improvement in quality of life and exercise tolerance.

The VecToR study again is a randomized trial of bi-ventricular pacing in patients with dilated cardiomyopathy, NYHA class II-IV and QRS duration >140ms. Endpoints are similar to the COMPANION trial.

The PAVE trial: Patients undergoing AV Node ablation secondary to chronic AF are randomized to Rt. Ventricular, LV or bi-ventricular stimulation. The study is powered to evaluate the effect on exercise tolerance and QOL.

Future Directions in BiVentricular Pacing Research

  1. Optimal site for LV pacing is still to be determined. Preliminary data suggest that the mid lateral LV pacing may produce best results.
  2. The LV lead technology will also need to be improved. New leads may offer access to, and stability within, veins otherwise inaccessible to the pacing specialist. The Guidant Easy-Track lead system and the Medtronic 10512 lead are currently in investigational protocols.
  3. It is still not known whether lone LV pacing can provide equivalent or even superior results in comparison with bi-ventricular pacing.
  4. Baseline QRS widening necessary for improvement with bi-ventricular pacing has to be investigated.
  5. Since patients who are candidates for bi-ventricular pacing are also at risk for sudden cardiac death, it is not known if combined use of bi-ventricular pacemaker and implantable cardioverter defibrilator may be associated with reduction in total mortality.

Conclusions

Placement of a LV lead transvenously can be achieved safely with a high degree of success. Based on the results of the MIRACLE trial, biventricular pacing for treatment of certain patients with congestive heart failure has been approved by the FDA. Several trials are still undergoing enrollment to evaluate clinical improvement with this form of therapy. Effect of bi-ventricular pacing on mortality is not known. Economic benefit studies also need to be conducted to evaluate the cost/benefit of this therapy.

www.dcmsonline.org February, 2002/ Jacksonville Medicine

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