Predictors of systolic augmentation from left ventricular preexcitation in patients with dilated cardiomyopathy and intraventricular conduction delay

Echocardiographic quantification of left ventricular asynchrony predicts an acute hemodynamic benefit of cardiac resynchronization therapy

OBJECTIVES

We sought to determine whether radial left ventricular (LV) asynchrony in patients with heart failure predicts systolic function improvement with cardiac resynchronization therapy (CRT).

BACKGROUND

We quantified LV wall motion by echocardiography to correlate the effects of CRT on LV systolic function with wall motion synchrony.

METHODS

Thirty-four patients underwent echocardiographic phase analysis of LV septal and lateral wall motion and hemodynamic testing before CRT. Phase relationships were measured by the difference between the lateral (Phi(L)) and septal (Phi(S)) wall motion phase angles: Phi(LS) = Phi(L) - Phi(S). The absolute value of Phi(LS) was used as an order-independent measure of synchrony: the absolute value Phi(LS) = the absolute value of Phi(L) - Phi(S).

RESULTS

Three phase relationships were identified (mean +/- SD): type 1 (n = 4; peak positive LV pressure [dP/dt(max)] 692 +/- 310 mm Hg/s; Phi(LS) = 5 +/- 6 degrees, synchronous wall motion); type 2 (n = 17; dP/dt(max) 532 +/- 148 mm Hg/s; Phi(LS) = 77 +/- 33 degrees, delayed lateral wall motion); and type 3 (n = 13; dP/dt(max) 558 +/- 154 mm Hg/s; Phi(LS) = -115 +/- 33 degrees, delayed septal wall motion, triphasic). A large absolute value of Phi(LS) predicted a larger increase in dP/dt(max) with CRT (r = 0.74, p < 0.001). Sixteen patients were studied during right ventricular (RV), LV and biventricular (BV) pacing. Cardiac resynchronization therapy acutely reduced the absolute value of Phi(LS) from 104 +/- 41 degrees (OFF) to 86 +/- 45 degrees (RV; p = 0.14 vs. OFF), 71 +/- 50 degrees (LV; p = 0.001 vs. OFF) and 66 +/- 42 degrees (BV; p = 0.001 vs. OFF). A reduction in the absolute value of Phi(LS) predicted an improvement in dP/dt(max) in type 2 patients for LV (r = 0.87, p = 0.005) and BV CRT (r = 0.73, p = 0.04).

CONCLUSIONS

Echocardiographic quantification of LV asynchrony identifies patients likely to have improved systolic function with CRT. Improved synchrony is directly related to improved hemodynamic systolic function in type 2 patients.

Resynchronization Therapy for Congestive Heart Failure

Ventricular contraction is achieved by the coordinated electrical activation of the ventricles through the action of the cardiac conduction system. In the presence of left bundle branch block (LBBB) or interventricular conduction delay (IVCD), the ventricular contraction pattern is desynchronized and the stroke volume is reduced as a consequence. In patients with congestive heart failure (CHF) due to systolic dysfunction, the presence of LBBB or IVCD further degrades ventricular function, contributing directly to the severity of their CHF symptoms. Cardiac resynchronization therapy (CRT) through biventricular pacing relieves CHF symptoms and improves functional status in patients with medically refractory heart failure due to left ventricular systolic dysfunction and LBBB or IVCD. The benefits of CRT are due to improvement in the ventricular activation sequence, resulting in a more coordinated and efficient ventricular contraction. In addition to symptomatic benefits, available data support the hypothesis that CRT alters the natural history of CHF in patients with intraventricular conduction delay.

Early and late QRS morphology and width in biventricular pacing: relationship to lead site and electrical remodeling

48 patients (40 Male), mean age 68 +/- 8 years, in III-IV class, with intraventricular conduction delay, received a biventricular pacemaker. Heart failure aetiology was non-ischemic in 60%. Left ventricular lead positioning was inferior in 5 patients (10%), posterior in 12 (25%), lateral in 18 (37%) and anterior in 13 (27%). QRS duration and axis were evaluated in sinus rhythm, and during right ventricular pacing, left ventricular pacing and biventricular pacing, the last early after implant and late after 8.8 +/- 4.3 months. QRS duration (ms) was 154 +/- 29 in sinus rhythm, 175 +/- 28 during right ventricular pacing, 196 +/- 31 during left ventricular pacing, 122 +/- 23 during biventricular pacing "early" and 120 +/- 18 during biventricular pacing "late." All the differences were statistically significant, but not between "early" and "late" biventricular pacing. Mean QRS axis ( degrees ) was -27 +/- 32 in sinus rhythm, -75 +/- 4 during right ventricular pacing, 112 +/- 41 during left ventricular pacing, -82 +/- 51 during biventricular pacing "early" and -80 +/- 42 during biventricular pacing "late." Only the difference between left ventricular pacing and all the other groups was statistically significant. QRS axis did not significantly differ according to left ventricular lead site during left and biventricular pacing. "Late" compared with "early" biventricular pacing axis showed variation >30 degrees in 35% of patients, in spite of no significant changes in QRS duration and x-ray positioning.

CONCLUSION

Biventricular pacing significantly reduced QRS width, which persisted long-term. Left and biventricular pacing axis was poorly related to left ventricular lead positioning. Biventricular pacing axis variability over time may suggest a role of electrical remodeling.

Quantitation of basal dyssynchrony and acute resynchronization from left or biventricular pacing by novel echo-contrast variability imaging

OBJECTIVES

This study sought to test a novel echocardiographic method based on contrast variability imaging (CVI), to quantify cardiac dyssynchrony and magnitude of resynchronization achieved by left ventricular (LV) and biventricular (BiV) pacing therapy.

BACKGROUND

Left ventricular or BiV pacing is a promising new therapy for patients with heart failure and intraventricular conduction delay. However, precise quantitation of the extent of resynchronization achieved remains scant.

METHODS

Ten patients treated with BiV or LV pacing therapy were studied. Echo-contrast was infused slowly, and gated images were acquired before and during contrast appearance. The temporally normalized variance derived from 30 to 50 sequential beats was determined at each pixel to yield the CVI image-displaying improved wall delineation. Systolic regional fractional area of radial sectors was calculated with active and temporarily suspended (AAI) pacing. All analyses were performed blinded to both patient and treatment.

RESULTS

Pacing increased septal inward motion from -20.4 +/- 9.6% to -30.5 +/- 14.0%, whereas lateral wall motion occurred earlier with no net magnitude change. Both spatial and temporal dyssynchrony in the LV declined nearly 40% with LV or BiV pacing (p < or = 0.001), and this correlated with increasing ejection fraction (31% to 39%; p < 0.02; p < 0.004 for correlation with dyssynchrony).

CONCLUSIONS

The new imaging and regional dyssynchrony analysis methods provide quantitative assessment of resynchronization analogous to that previously obtained only by tagged magnetic resonance imaging. This could provide a useful noninvasive method for both identifying candidates and following long-term therapy.

Current status and future expectations for multisite pacing in heart failure

The number of patients with congestive heart failure (CHF) has achieved astonishing proportions. It is a debilitating and usually lethal condition, aside from being responsible for an enormous proportion of health care expenditures. Advances in medical therapy have not been sufficient to significantly improve prognosis, and heart transplantation can only benefit a minority of patients. Biventricular pacing has emerged as a promising form of therapy for patients with severe, medical refractory CHF with ventricular conduction defects. However, there are many technical issues to be solved, and better methods of selecting patients who respond favorably to this form of therapy are yet to be developed. This article reviews the rationale, delivery modes, and available data supporting multisite cardiac pacing as an alternative form of therapy for the failing heart.

Cardiac contractility modulation by electric currents applied during the refractory period

Inotropic effects of electric currents applied during the refractory period have been reported in cardiac muscle in vitro using voltage-clamp techniques. We investigated how electric currents modulate cardiac contractility in normal canine hearts in vivo. Six dogs were instrumented to measure regional segment length, ventricular volume (sonomicrometry), and ventricular pressure. Cardiac contractility modulating (CCM) electric currents (biphasic square pulses, amplitude +/-20 mA, total duration 30 ms) were delivered during the refractory period between pairs of electrodes placed on anterior and posterior walls. CCM significantly increased index of global contractility (E(es)) from 5.9 +/- 2.9 to 8.3 +/- 4.6 mmHg/ml with anterior CCM, from 5.3 +/- 1.8 to 8.9 +/- 4.0 mmHg/ml with posterior CCM, and from 6.1 +/- 2.6 to 11.0 +/- 7.0 mmHg/ml with combined CCM (P < 0.01, no significant change in volume axis intercept). End-systolic pressure-segment length relations showed contractility enhancement near CCM delivery sites, but not remotely. Relaxation was not influenced. CCM increased mean aortic pressure, but did not change peripheral resistance. Locally applied electrical currents enhanced global cardiac contractility via regional changes in myocardial contractility without impairing relaxation in situ.

Cardiac resynchronization therapy restores optimal atrioventricular mechanical timing in heart failure patients with ventricular conduction delay

We characterized the relationship between systolic ventricular function and left ventricular (LV) end-diastolic pressure (LVEDP) in patients with heart failure (HF) and baseline asynchrony during ventricular stimulation. The role of preload in the systolic performance improvement that can be obtained in HF patients with LV stimulation is uncertain.We measured the maximum rate of increase of LV pressure, LVEDP, aortic pulse pressure (PP) and the atrioventricular mechanical latency (AVL) between left atrial systole and LV pressure onset in 39 patients with HF. Two subgroups were identified: "responder" if PP improved, or "nonresponder."Maximum hemodynamic improvement occurred at an atrioventricular (AV) delay that did not decrease LVEDP. Left ventricular and biventricular (BV) stimulation increased systolic hemodynamics significantly, despite no significant increase in LVEDP. All parameters decreased when the LVEDP was decreased by shorter AV delay. Left ventricular and BV stimulation provided better hemodynamics than right ventricular (RV) stimulation. For the nonresponder subgroup, systolic hemodynamics only worsened during AV delay shortening. For the responder subgroup, optimum PP was achieved when AVL was near zero. Restoration of optimal left atrial-ventricular mechanical timing partly contributes to the hemodynamic improvements observed in this patient subgroup. However, preload alone cannot explain the differences seen between RV and BV stimulation and the contradictory PP decreases even at maximal preload in the nonresponder subgroup. These results may be explained by a site-dependent mechanism such as the degree of ventricular synchrony. Caution should be taken in these patients when optimizing AV delays using echocardiography techniques that focus on LV inflow.

Management of heart failure: use of biventricular pacing

Congestive heart failure (CHF) is a clinical syndrome that affects more than 4 million people in the United States. The grim prognosis for this population has led to a search for new therapies to treat CHF. Resynchronization of the ventricles is one such therapy. The pathophysiology associated with conduction defects and the evolution of the use of pacing technologies for this patient population will be discussed. Early data have been encouraging, suggesting that patients may gain important hemodynamic, functional, and quality-of-life improvements with biventricular pacing.

Retiming the failing heart: principles and current clinical status of cardiac resynchronization

Left or biventricular (BiV) pacing, or cardiac resynchronization therapy, was proposed nearly 10 years ago as an adjunctive treatment for patients with advanced heart failure (HF) complicated by discoordinate contraction due to intraventricular conduction delay. Since then, both short-term and a growing number of long-term clinical trials have reported on the mechanisms and short- and mid-term efficacy of this approach, with encouraging results. Therapy is implemented with novel pacing systems incorporating an endocardial lead to stimulate the lateral free wall via a cardiac vein, and often a right ventricular (RV) apex lead to provide BiV stimulation. A third atrial sensing lead monitors intrinsic rhythm and provides timing data to ensure ventricular pre-excitation. Modulation of the electronic atrial-ventricular (AV) time delay can optimize contractile synchrony, enhance the contribution of atrial systole, and reduce mitral regurgitation. Individuals with advanced HF, a wide QRS complex often with an AV time delay, and evidence of contraction dyssynchrony in viable myocardium represent the target patient group. Short-term studies reveal systolic augmentation and chamber efficiency from pacing resynchronization that can be substantial. Long-term studies reveal improved symptoms and exercise capacity, and some report reversal of chronic cardiac dilation. However, important questions regarding long-term efficacy and mortality impact, optimal mode for pacing stimulation, and role of combined pacing/cardioverter/defibrillation devices remain unresolved. Here we review pathophysiologic mechanisms, short- and long-term clinical results, and future directions of this new and promising therapy.

Biventricular pacing in congestive heart failure: a boost toward finer living

With 550,000 new cases each year, congestive heart failure is a major medical problem. Several medical therapies, including digoxin, angiotensin-converting enzyme inhibitors, and beta-blockers, have reduced the number of re-hospitalizations and slowed the progression of congestive heart failure. Angiotensin-converting enzyme inhibitors, some beta-blockers, and the combination of hydralazine with nitrates have improved survival. Despite these benefits, medical therapy frequently fails to improve quality of life. Biventricular pacing has been introduced to resynchronize mechanical and electrical asynchrony frequently observed in patients with heart failure. The most recent pacing trials show an improvement in quality of life and functional class. Long-term data are needed to determine the effect of biventricular pacing on survival. The acute hemodynamic studies suggest that resynchronization pacing therapy may predict a positive long-term benefit for many patients with congestive heart failure.

Echocardiographic prediction of long-term response to biventricular pacemaker in severe heart failure

BACKGROUND

Biventricular pacing substantially improves LV systolic function and symptom status in some patients with dilated cardiomyopathy.

AIMS

To assess whether the long-term benefit could be predicted from the echocardiographic parameters.

METHODS AND RESULTS

Sixteen patients with dilated cardiomyopathy who underwent atrio-biventricular pacemaker implantation were analyzed in two groups: the responders (n=11) were those with a symptomatic improvement of one or more NYHA functional class; the non-responders (n=5) failed to improve at follow-up (7.6+/-5 months). Echocardiography was performed at baseline, the day after the implantation and then every 3 months. Besides the conventional parameters, the following variables were included: LV diastolic filling time (DFT); the duration of mitral regurgitation (dMR); and LV dP/dt obtained from the continuous wave mitral regurgitation curve. While the baseline DFT and dP/dt were not significantly different between non-responders and responders (256+/-105 vs. 358+/-115, P=0.14 and 564+/-199 vs. 468+/-117, P=0.44, respectively), the QRS width (149+/-15 vs. 175+/-24 ms, P=0.05) and the dMR (343+/-70 vs. 443+/-49 ms, P=0.007) were higher in the responders. The changes of dMR, DFT and QRS width by pacing were not significantly different between groups (P=0.18, 0.30 and 0.77, respectively). However, the change of LV dP/dt by pacing in the responders was significantly different than for non-responders (from 468+/-117 to 676+/-216 mmHg/s vs. from 564+/-199 to 483+/-94, P=0.002). An acute increase in LV dP/dt over 22% by pacing yielded only two false negatives and no false positives in predicting the long-term responsiveness.

CONCLUSION

Patients with longer QRS and dMR are more likely to benefit from atrio-biventricular stimulation. The acute changes of Doppler derived LV dP/dt may provide valuable information in predicting the long-term response to biventricular pacing.

Effects of single- and biventricular pacing on temporal and spatial dynamics of ventricular contraction

Resynchronization is frequently used for the treatment of heart failure, but the mechanism for improvement is not entirely clear. In the present study, the temporal synchrony and spatiotemporal distribution of left ventricular (LV) contraction was investigated in eight dogs during right atrial (RA), right ventricular apex (RVa), and biventricular (BiV) pacing using tagged magnetic resonance imaging. Mechanical activation (MA; the onset of circumferential shortening) was calculated from the images throughout the left ventricle for each pacing protocol. MA width (time for 20-90% of the left ventricle to contract) was significantly shorter during RA (43.6 +/- 17.1 ms) than BiV and RVa pacing (67.4 +/- 15.2 and 77.6 +/- 16.4 ms, respectively). The activation delay vector (net delay in MA from one side of the left ventricle to the other) was significantly shorter during RA (18.9 +/- 8.1 ms) and BiV (34.2 +/- 18.3 ms) than during RVa (73.8 +/- 16.3 ms) pacing. Rate of LV pressure increase was significantly lower during RVa than RA pacing (1,070 +/- 370 vs. 1,560 +/- 300 mmHg/s) with intermediate values for BiV pacing (1,310 +/- 220 mmHg/s). BiV pacing has a greater impact on correcting the spatial distribution of LV contraction than on improving the temporal synchronization of contraction. Spatiotemporal distribution of contraction may be an important determinant of ventricular function.

Patient selection for biventricular pacing

INTRODUCTION

Biventricular pacing improves functional status in the majority of patients with drug-refractory heart failure, dilated cardiomyopathy, and interventricular conduction delay. The aim of this study was to analyze the baseline clinical and functional data of a cohort of patients implanted with a biventricular stimulation system in a single-center experience, to verify if the pathophysiologic characteristics of patients affect outcome, and to determine if preliminary identification of the right candidates for the new therapy is possible with noninvasive parameters.

METHODS AND RESULTS

Since March 1999, 52 patients with advanced heart failure (idiopathic cardiomyopathy 50%, ischemic cardiomyopathy 35%, other etiology 15%) and left bundle branch block underwent cardiac resynchronization and were followed prospectively. Paired analysis over mean (+/- SD) follow-up of 348 +/- 154 days showed an overall significant decrease of QRS width (baseline 194 +/- 33.2 msec vs follow-up 159.6 +/- 20.1 msec), New York Heart Association (NYHA) functional class (baseline 3.2 +/- 0.5 vs follow-up 2.3 +/- 0.5), quality-of-life score (baseline 54 +/- 25 vs follow-up 25 +/- 16), and increase of maximal VO2 (baseline 12.6 +/- 2.5 mL/kg/min vs follow-up 15.0 +/- 3.3 mL/kg/min). There were 80% responders (documented, persistent decrease > or = 1 NYHA class) and 20% nonresponders (same NYHA class or decline of status; need for heart transplant; death due to progressive pump failure). No significant differences in baseline clinical and functional variables between the two subgroups were observed. In responders, there was a highly significant global improvement of all variables; in nonresponders, no parameters changed between baseline and follow-up.

CONCLUSION

These data confirm the role of biventricular pacing in improving the functional status of the great majority of a selected patient population having advanced heart failure and left bundle branch block with wide QRS complex. Basal demographic, clinical, and functional characteristics are not helpful in preliminary selection of responders. Simple evaluation of NYHA class confirms favorable outcome (improvement of functional and hemodynamic status).

Biventricular pacing for heart failure

The completed trials of biventricular pacing in congestive cardiac failure are impressively encouraging as a novel therapy for the symptoms of a most devastating disease. The actual delivery of the LV pacing hardware and final patient selection criteria require further refinement, as it is clear that not all patients with heart failure respond favorably. What is clear is that all patients should be prescribed maximally tolerated, proven medical therapy before assessment as to the feasibility of biventricular pacing therapy. This should be the case until potentially proven otherwise in newly planned trials designed to assess the comparative efficacy of both approaches. It is difficult to see that the two approaches should be anything but complementary in their benefit. The expense and potential complication associated with any invasive procedure needs to be considered, however, and it would seem reasonable that all of these patients should be receiving maximally tolerated medical therapy before and after the implantation of a device. Finally, the effect of this therapy on mortality needs to be assessed and, consequently, the requirement for defibrillation capability considered in this population of patients with a known high incidence of sudden death.

Emerging indications for cardiac pacing

Substantial data have been accumulated and indications have been well delineated for pacemaker implantation in the treatment of sinus node dysfunction and heart block. However, many other indications have been proposed for pacemaker implantation. In this review, the authors examine available data regarding pacemaker implantation for new indications: neurally mediated syncope, hypertrophic obstructive cardiomyopathy, congestive heart failure, prevention of atrial fibrillation, and the relative merits of single-chamber and dual-chamber pacemakers.

Three dimensional echocardiography documents haemodynamic improvement by biventricular pacing in patients with severe heart failure

OBJECTIVES

To quantify the short term haemodynamic effects of biventricular pacing in patients with heart failure and left bundle branch block by using three dimensional echocardiography.

DESIGN

Three dimensional echocardiography was performed in 15 consecutive heart failure patients (New York Heart Association functional class III or IV) with an implanted biventricular pacing system. Six minute walk tests were performed to investigate the effect of biventricular pacing on exercise capacity. Data were acquired at sinus rhythm and after short term (2–7 days) biventricular pacing.

RESULTS

Compared with baseline values, biventricular pacing significantly reduced left ventricular end diastolic volume (EDV) by mean (SD) 4.0 (5.1)% (p < 0.01) and end systolic volume (ESV) by 5.6 (6.4)% (p < 0.02). Mitral regurgitant fraction was significantly reduced by 11 (12.1)% (p < 0.003) and forward stroke volume (FSV) increased by 13.9 (18.6)% (p < 0.02). Exercise capacity was significantly improved with biventricular pacing by 48.4 (43.3)% (p < 0.00001). Regression analyses showed that the percentage increase in FSV independently predicted percentage improvement in walking distance (r2 = 0.73, p < 0.0002). Both basal QRS duration and QRS narrowing predicted pacing efficacy, showing a significant correlation with %ΔEDV, %ΔESV, and %ΔFSV.

CONCLUSIONS

In five of 15 consecutive patients with heart failure and left bundle branch block, biventricular pacing induced a more than 15% increase in FSV, which predicted a more than 25% increase in walking distance and was accompanied by an immediate reduction in left ventricular chamber size and mitral regurgitation.

Three dimensional echocardiography documents haemodynamic improvement by biventricular pacing in patients with severe heart failure

OBJECTIVES

To quantify the short term haemodynamic effects of biventricular pacing in patients with heart failure and left bundle branch block by using three dimensional echocardiography.

DESIGN

Three dimensional echocardiography was performed in 15 consecutive heart failure patients (New York Heart Association functional class III or IV) with an implanted biventricular pacing system. Six minute walk tests were performed to investigate the effect of biventricular pacing on exercise capacity. Data were acquired at sinus rhythm and after short term (2-7 days) biventricular pacing.

RESULTS

Compared with baseline values, biventricular pacing significantly reduced left ventricular end diastolic volume (EDV) by mean (SD) 4.0 (5.1)% (p < 0.01) and end systolic volume (ESV) by 5.6 (6.4)% (p < 0.02). Mitral regurgitant fraction was significantly reduced by 11 (12.1)% (p < 0.003) and forward stroke volume (FSV) increased by 13.9 (18.6)% (p < 0.02). Exercise capacity was significantly improved with biventricular pacing by 48.4 (43.3)% (p < 0.00001). Regression analyses showed that the percentage increase in FSV independently predicted percentage improvement in walking distance (r(2) = 0.73, p < 0.0002). Both basal QRS duration and QRS narrowing predicted pacing efficacy, showing a significant correlation with %DeltaEDV, %DeltaESV, and %DeltaFSV.

CONCLUSIONS

In five of 15 consecutive patients with heart failure and left bundle branch block, biventricular pacing induced a more than 15% increase in FSV, which predicted a more than 25% increase in walking distance and was accompanied by an immediate reduction in left ventricular chamber size and mitral regurgitation.

Pacing for heart failure

Pacing for patients with severe heart failure without bradyarrhythmia has been proposed as an addition to medical therapy over the past decade. Alteration of the normal electrical activation sequence of the heart modifies its mechanical action, especially when ventricular function is poor. Both the site of ventricular-lead placement and timing with the atria have been manipulated in attempts to alleviate the symptoms of heart failure. Most recently, in addition to the conventional two leads used for pacing, a third lead to pace the left ventricle has been advocated in some patients with heart failure. We review the evidence for pacing in heart failure.

Upcoming therapies for heart failure

Treatment of maladaptive neurohormonal activation in congestive heart failure (CHF) has been successful because basic cardiovascular science findings have been confirmed or dismissed through the use of well-controlled, large-scale clinical trials. It should be no surprise that this exciting approach is evolving toward novel agents and devices directed toward other pathways involved in CHF neurohormonal/cytokine activation. Several of these are in advanced clinical development and are likely to play prominent roles in CHF therapy in the near future.

Effects of multisite biventricular pacing in patients with heart failure and intraventricular conduction delay

BACKGROUND

One third of patients with chronic heart failure have electrocardiographic evidence of a major intraventricular conduction delay, which may worsen left ventricular systolic dysfunction through asynchronous ventricular contraction. Uncontrolled studies suggest that multisite biventricular pacing improves hemodynamics and well-being by reducing ventricular asynchrony. We assessed the clinical efficacy and safety of this new therapy.

METHODS

Sixty-seven patients with severe heart failure (New York Heart Association class III) due to chronic left ventricular systolic dysfunction, with normal sinus rhythm and a duration of the QRS interval of more than 150 msec, received transvenous atriobiventricular pacemakers (with leads in one atrium and each ventricle). This single-blind, randomized, controlled crossover study compared the responses of the patients during two periods: a three-month period of inactive pacing (ventricular inhibited pacing at a basic rate of 40 bpm) and a three-month period of active (atriobiventricular) pacing. The primary end point was the distance walked in six minutes; the secondary end points were the quality of life as measured by questionnaire, peak oxygen consumption, hospitalizations related to heart failure, the patients' treatment preference (active vs. inactive pacing), and the mortality rate.

RESULTS

Nine patients were withdrawn from the study before randomization, and 10 failed to complete both study periods. Thus, 48 patients completed both phases of the study. The mean distance walked in six minutes was 22 percent greater with active pacing (399+/-100 m vs. 326+/-134 m, P<0.001), the quality-of-life score improved by 32 percent (P<0.001), peak oxygen uptake increased by 8 percent (P<0.03), hospitalizations were decreased by two thirds (P<0.05), and active pacing was preferred by 85 percent of the patients (P<0.001).

CONCLUSIONS

Although it is technically complex, atriobiventricular pacing significantly improves exercise tolerance and quality of life in patients with chronic heart failure and intraventricular conduction delay.

Biventricular pacing in heart failure: update on results from clinical trials

Biventricular pacing or resynchronisation therapy is a non-pharmacological therapy for patients with chronic heart failure. Since being originally described in 1994, biventricular pacing has become a subject of intense interest and investigation. This review analyses the results reported in observational series and randomised trials, and seeks to answer two questions. If it works, why does it work? Which heart failure patients will it benefit?