Biventricular Resynchronization for Severe Heart Failure
Abstract & Commentary
Synopsis: Optimization of intraventricular activation intervals using sequential pacing provides further improvement in cardiac function in patients with left bundle branch block and congestive heart failure.
Source: Sogaard P, et al. Circulation. 2002;106: 2078-2084.
In this paper, sogaard and associates report a technique for the use of tissue Doppler imaging to optimize pacemaker program settings in biventricular devices used for the treatment of heart failure. Twenty patients participated in this elegant study. All had been referred for implantation of a biventricular pacemaker. The goal of biventricular pacing, also called cardiac resynchronization therapy (CRT), is to eliminate the negative hemodynamic effects seen with prolongation intraventricular conduction and activation. The patients had a mean age of 66 ± 8 years. Eleven had ischemic heart disease and 9 had nonischemic heart disease. All had sinus rhythm with chronic left bundle branch block and a QRS duration of at least 130 msec. The mean (±SD) QRS duration was markedly prolonged at 176 ± 25 msec. All patients were being treated with a standard heart failure regimen that included ACE inhibitors, diuretics, beta-blockers, and spironolactone. At the time of implant, 3 transvenous pacing leads were inserted, one positioned in the right atrium, one on the high intraventricular septum, and one on the left ventricular epicardial free wall via the coronary sinus. The high intraventricular septum was selected for the right ventricular lead to mimic normal right-sided activation and to get the widest difference in electrical activity recorded by the right ventricular and the left ventricular leads. The leads were connected to a dual chamber biventricular pacemaker with a programmable delay between the 2 ventricular outputs. Atrioventricular (AV) interval optimization was performed by determining the longest possible AV interval that did not result in truncation on the A wave measured by pulsed Doppler analysis of transmitral flow.
Three-dimensional echo and tissue Doppler recordings were performed on the day preceding and on the day after the pacemaker was implanted. Measurements were also repeated at 3 months. Measurements after implantation were performed during simultaneous right and left ventricular pacing and using 5 different intraventricular delay intervals (12, 20, 40, 60, and 80 msec) with either left ventricular or right ventricular preactivation. Thus, a total of 11 different intraventricular delays were examined with an equilibrium period of 10 minutes between each examination. Off-line analysis of the 3-D echocardiograms were performed and left ventricular end diastolic and end systolic volumes and ejection fractions were calculated. Using a 16-segment model, the percentage of segments with delayed longitudinal contraction was determined. In addition, the global systolic contraction amplitude (GSCA) was calculated as the average shortening amplitude of all 16 segments.
In patients with idiopathic dilated cardiomyopathy, delayed longitudinal contraction tends to be located in the lateral and posterior walls of the left ventricle. In patients with ischemic cardiomyopathy, abnormalities in contraction were more frequent in the septum and in the inferior wall. Exceptions to these general observations were however noted in both groups. Simultaneous biventricular pacing reduced the percentage of segments displaying delayed longitudinal contraction from 48.6 ± 16% to 23.2 ± 13%. The mean left ventricular ejection fraction improved from 22.4% to 29.7%. GSCA index increased by 32.6%. Sequential pacing using the optimal interventricular pacing interval could improve these parameters in all patients. However, no uniform pattern was observed. Left ventricular preactivation was superior in 9 patients whereas right ventricular preactivation was superior in the remaining 11 patients. For example, the ejection fraction improved from 22.4% ± 6% at baseline to 29.7 ± 5% with simultaneous biventricular pacing and further to 33.6 ± 6% with the optimal sequential ventricular pacing interval. The range of optimal preactivation intervals was narrow, with a range of 12-20 msec. Further increases in intraventricular delay decreased hemodynamic function.
Sogaard et al concluded that optimization of intraventricular activation intervals using sequential pacing provides further improvement in cardiac function in patients with left bundle branch block and congestive heart failure.
Comment by John P. DiMarco, MD, PhD
Cardiac resynchronization therapy is a new technique for improving symptoms of heart failure in patients with intraventricular conduction delays. In large trials, approximately 60-70% of patients treated with CRT have shown improvement in their heart failure symptom scores and during functional testing. Up until now, FDA- approved devices have all paced the right and left ventricle simultaneously. In this paper, Sogaard et al show that careful analysis of hemodynamic function using tissue Doppler imaging after changes in the pacing interval between the 2 ventricular leads can result in further improvements in cardiac function. Individual patients respond better to having early activation of either right or left ventricle. This may allow even a higher fraction of patients to achieve functional improvement with cardiac resynchronization.
This is an interesting preliminary study. However, it remains to be seen if this technique will actually result in long-term clinical benefit. Measurements made here were with the patient supine and at rest. It is not known if these hemodynamic changes would be consistent during physical activity or in the upright position. Also, the protocol used is involved and takes several hours to perform. This would be difficult to implement in a busy clinical practice. Finally, Sogaard et al placed their right ventricular lead high on the septum. Although this may be optimal for pacing it may not be optimal for defibrillation and many patients who receive a CRT device also need a defibrillator.
Resynchronization therapy offers potential benefits to many patients. The first generation devices only permit simultaneous right and left ventricular pacing. We can hope that further careful studies like this one will encourage the inclusion of more flexible programming that may further improve responses to CRT.
Dr. DiMarco is Professor of Medicine, Division of Cardiology University of Virginia, Charlottesville.
In this paper, sogaard and associates report a technique for the use of tissue Doppler imaging to optimize pacemaker program settings in biventricular devices used for the treatment of heart failure.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content. TESTING
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