Hemodynamic implications of left bundle branch block

Persistent left bundle branch block in a patient with dilated cardiomyopathy that improved with low dose carvedilol therapy

A 43-year-old Japanese woman with dilated cardiomyopathy had complete left ventricular bundle branch block (CLBBB), which had persisted for at least two years. At the time of admission, the serum brain natriuretic peptide (BNP) concentration was 502 pg/mL (normal range, 0-18 pg/mL), the left ventricular diastolic dimension (LVDd) was 59 mm, the left ventricular systolic dimension (LVDs) was 54 mm, the %fractional shortening (FS) was 8%, and the left ventricular ejection fraction (LVEF) was 19.7% by echocardiography. Low dose carvedilol was initiated for the treatment of heart failure. Adverse effects, such as progression of cardiac conduction disturbances, did not occur after initiation of carvedilol therapy. About one year after initiation of carvedilol therapy, the CLBBB disappeared and a significant improvement in left ventricular function was noted. The LVDd was 44 mm, the LVDs was 30 mm, the %FS was 33%, and the LVEF was 61%, and the serum BNP concentration was decreased to 18.5 pg/mL. We describe a case in which low dose carvedilol was effective for treating both CLBBB and left ventricular function.

Evaluation of left ventricular diastolic functions in patients with frequent premature ventricular contractions from right ventricular outflow tract

This study was sought to examine the effects of repetitive monomorphic premature ventricular contractions (PVCs) on left ventricular (LV) diastolic function. Thirty-three symptomatic patients (Study group, 10 males, mean age 40 +/- 8 years) with normal LV systolic function and repetitive PVCs originating from the right ventricular outflow tract (RVOT-PVCs) on 24-h Holter monitoring, and 30 healthy controls (Control group, 9 males, mean age 37 +/- 9 years) were enrolled in the study. None of the patients had structural heart disease. Diastolic function was assessed by echocardiographic mitral inflow pattern and tissue Doppler imaging. The study group displayed a lower E/A ratio, longer isovolumetric relaxation time (IVRT), and longer E-wave deceleration time (EDT). In the study group 13 patients showed impaired relaxation. While mean values of the systolic velocity (Sa), early diastolic velocity (Ea), and early/late diastolic velocity (Ea/Aa) ratio were significantly lower in the study group, the Aa velocity and E/Ea ratio were significantly higher. Ea velocity was <10 cm/s in 7 study patients. Mitral inflow pattern and Ea velocity was normal in all controls. Significant correlations were found between ventricular premature beats percentage and early to late transmitral flow velocity ratio, EDT, IVRT, Ea velocity, the Ea/Aa ratio, and the E/Ea ratio. In multivariate analysis, total PVC count and age were found to be independent predictors of impaired relaxation. These results suggest that repetitive monomorphic RVOT-PVCs lead to abnormalities of LV diastolic function that may contribute to clinical symptoms in patients with structurally normal hearts.

Reversible left ventricular dyssynchrony and dysfunction resulting from right ventricular pre-excitation

We report observations in a 7-year-old girl with right ventricular pre-excitation due to an accessory atrioventricular pathway (AP), and depressed cardiac function. Echocardiographic findings consisted of left ventricular (LV) dilatation with asynchronous ventricular wall motion and diminished LV ejection fraction. Electrophysiological study revealed a para-Hisian AP. She underwent successful AP ablation, after which asynchronous ventricular wall motion disappeared. Cardiac size and function were normal after 3 months follow-up. These findings suggest that ventricular pre-excitation leading to asynchronous ventricular motion was a possible cause of LV dilation and dysfunction and that catheter ablation reversed undesirable cardiac remodelling in this patient.

Nonpharmacologic therapy in heart failure: an overview

Heart failure therapy has seen significant changes over the past few decades. Therapies aimed at various pathophysiologic states have been and are currently used in the treatment of heart failure. Despite this, incidence and mortality continue to rise. Nonpharmacologic therapy plays a significant and life-saving role in certain subsets of patients. This review will discuss the current evidence and future direction of nonpharmacologic therapy as it pertains to surgical options, devices, and exercise.

Left bundle-branch block--pathophysiology, prognosis, and clinical management

Given its broad use as a screening tool, the electrocardiogram (ECG) has largely become one of the most common diagnostic tests performed in routine clinical practice. As a result, the finding of left bundle-branch block (LBBB) in the absence of a well-defined clinical setting has become relatively frequent and raises questions and often concerns. While in the absence of clinically detectable heart disease LBBB does not necessarily imply poor outcomes, physicians should be aware of the role of LBBB in stratifying risk of cardiovascular events and death in subjects with both ischemic and nonischemic heart disease. This paper reviews historical landmarks, pathophysiologic features, prognostic implications, and clinical management of LBBB in apparently healthy subjects and those with heart disease.

Cardiac Resynchronization Treatment of Heart Failure

Cardiac resynchronization therapy (CRT) is well established as a treatment for patients with moderate to severe heart failure on optimal medical therapy. Early studies demonstrated improved functional capacity and evidence of reverse remodeling; more recently, CRT has been associated with a survival benefit in advanced heart failure both with and without a defibrillator. We review the eight landmark trials in CRT. To date, criteria have focused on electrical delay, but echocardiographic parameters emphasize the importance of mechanical delay or ventricular dyssynchrony. With the exponential rise in implants, new issues have emerged, such as optimal device programming, identifying appropriate candidates, and accounting for cases without clinical benefit from CRT.

The effects of ventricular asynchrony on myocardial perfusion

Asynchronous depolarization and contraction sequence, secondary to intraventricular conduction defects or to permanent right ventricular apical pacing, is associated with adverse effects that may be clinically evident in the failing heart. Experimental and clinical studies have suggested that asynchronous ventricular contraction deteriorates left ventricular performance and induces unfavourable left ventricular remodelling. Although such contraction does not appear to affect resting coronary artery blood flow, it increases endomyocardial pressure during diastole and decreases regional myocardial perfusion in the interventricular septum. The magnitude of these effects may correlate with the duration of the asynchrony. Despite these detrimental effects, there is no evidence that ventricular asynchrony reduces collateral myocardial blood flow, myocardial oxygen consumption or cardiac efficiency, neither in patients with normal coronary arteries, nor in patients with coronary artery disease. Furthermore, in patients with acute ischaemic syndromes, ventricular asynchrony exerts a neutral effect on the ischaemic myocardium. Cardiac resynchronization therapy improves left ventricular systolic and diastolic function without an increase in myocardial oxygen consumption or energy cost. This therapy may decrease the inhomogeneity in regional oxidative metabolism, myocardial perfusion and cardiac efficiency. Further experimental and clinical studies are needed on this area.

Comparison of myocardial contrast echocardiography with SPECT in the evaluation of coronary artery disease in asymptomatic patients with LBBB

OBJECTIVE

The non-invasive assessment of coronary artery disease (CAD) in patients with left bundle branch block (LBBB) is troublesome. In this study, we investigated the diagnostic accuracy of myocardial contrast echocardiography (MCE) with adenosine to detect CAD in asymptomatic patients with LBBB, and we compared it with single photon emission computed tomography (SPECT) with adenosine.

METHODS

Forty-seven patients with LBBB, and no previously documented CAD, initially underwent SPECT imaging and 1-3 days later MCE. Coronary arteriography was performed within 1 week from the latter procedure.

RESULTS

The overall sensitivity, specificity, positive predictive value, negative predictive value, diagnostic accuracy, and kappa index of concordance of SPECT were 73%, 72%, 44%, 90%, 72%, and 0.37+/-0.13, respectively, whereas those of MCE were 91%, 92%, 77%, 97%, 92%, and 0.77+/-0.1, respectively (p<0.05 for all comparisons). Significant CAD was present in 11 patients (23%). Left anterior descending coronary artery was involved in 8 patients, left circumflex artery in 2 patients, and right coronary artery in 4 patients. Concerning the left anterior descending artery disease detection, SPECT had a sensitivity of 75%, a specificity of 79%, a positive predictive value of 43%, a negative predictive value of 94%, and a diagnostic accuracy of 79%. The respective values of MCE were 100% for all of the above variables.

CONCLUSIONS

MCE with adenosine has a higher global diagnostic accuracy compared to SPECT for the detection of CAD in patients with LBBB, mainly due to the poor specificity of SPECT concerning perfusion defects detection in the left anterior descending artery territory.

The deleterious consequences of right ventricular apical pacing: time to seek alternate site pacing

BACKGROUND

The purpose of this article is to critically review the data accumulated to date from studies evaluating the hemodynamic and clinical effects of right ventricular apical pacing during conventional permanent cardiac pacing. The data from studies comparing the effects of right ventricular apical pacing and alternate site ventricular pacing are also reviewed.

METHODS

We conducted a MEDLINE and journal search of English-language reports published in the last decade and searched relevant papers.

RESULTS

Although intraventricular conduction delay in the form of left bundle branch block (LBBB) has traditionally been viewed as an electrophysiologic abnormality, it has now become abundantly clear that it has profound hemodynamic effects due to ventricular dyssynchrony, especially in patients with heart failure. These deleterious effects can be significantly ameliorated by cardiac resynchronization therapy effected by biventricular or left ventricular pacing. However, not only is spontaneous LBBB harmful, but the iatrogenic variety produced by right ventricular apical pacing in patients with permanent pacemakers may be equally deleterious. In this review new evidence from recent studies is presented, which strongly suggests a harmful effect of our long-standing practice of producing an iatrogenic LBBB by conventional right ventricular apical pacing in patients receiving permanent pacemakers. This emerging strong new evidence about the adverse hemodynamic and clinical effects of right ventricular apical pacing would dictate a reassessment of our traditional approach to permanent cardiac pacing and direct our attention to alternate sites of pacing, such as the left ventricle and/or the right ventricular outflow tract or septum, if not for all patients, at least for those with left ventricular dysfunction. Indeed, current convincing data on alternate site ventricular pacing are encouraging and this approach should be actively pursued and further investigated in future studies.

CONCLUSIONS

Not only is spontaneous permanent LBBB harmful to our patients, but the iatrogenic variety produced by right ventricular apical pacing during conventional permanent pacing may also be deleterious to some patients. The compelling evidence presented herein cannot be ignored; it may dictate a change of attitude toward right ventricular apical pacing directing our attention to alternate sites of ventricular pacing and avoidance of the right ventricular apex.

Implantable devices for management of chronic heart failure: defibrillators and biventricular pacing therapy

PURPOSE OF REVIEW

With chronic heart failure already an epidemic in the USA, its prevalence is expected to rise significantly in the future. Despite improved survival with pharmacologic therapy, the morbidity and mortality of patients with heart failure remain high. The purpose of this review, therefore, is to present recent data on the non-pharmacologic, device-based treatment of patients with chronic heart failure.

RECENT FINDINGS

The implantable cardioverter-defibrillator has become standard treatment for the prevention of sudden, arrhythmic death. Recent well-designed clinical trials have led to device-based therapy as an important component in the management of patients with systolic left ventricular dysfunction (resulting from both ischemic and non-ischemic etiologies) and symptomatic chronic heart failure. Implantable cardioverter-defibrillator therapy alone (without biventricular pacing) results in a significant reduction in the overall mortality of patients with mild and moderate heart failure. Biventricular pacing (or cardiac resynchronization therapy) with or without a back-up implantable cardioverter-defibrillator, compared with optimal pharmacologic therapy, improves symptoms, quality of life, exercise tolerance, left ventricular function, and the survival of patients with advanced heart failure, a left ventricular ejection fraction of 35% or less, and intraventricular conduction delays (QRS > 120 ms), although up to approximately 30% of patients do not respond to cardiac resynchronization therapy. Ongoing and planned studies should clarify which patients are most likely to respond to cardiac resynchronization therapy and elucidate its role in those with a normal (< 120 ms) QRS (approximately 70% of patients with heart failure).

SUMMARY

Device therapy (implantable cardioverter-defibrillator and cardiac resynchronization therapy) should be considered an integral, but adjunctive, part of the management of patients with chronic heart failure who are receiving appropriate medical therapy. The type of device used will depend on the individual patient's clinical characteristics.

Cardiac Resynchronization Therapy

Left ventricular (LV) dysynchrony, generally defined as the effect of intraventricular conduction defects or bundle branch block to produce nonsynchronous ventricular activation, places the failing heart at a further mechanical disadvantage. The deleterious effects of ventricular dysynchrony include suboptimal ventricular filling, paradoxical septal wall motion, reduced LV contractility, increased mitral regurgitation, and poor clinical outcomes (eg, increased hospitalization and mortality). The clinical and mechanical manifestations of ventricular dysynchrony can be treated by simultaneously pacing both the right and left ventricles usually in association with right atrial sensing, resulting in atrial-synchronized biventricular pacing or cardiac resynchronization therapy (CRT). The weight of evidence supporting the routine use of CRT in patients with heart failure with ventricular dysynchrony is now quite substantial. More than 4000 patients have been evaluated in randomized controlled trials of CRT, and several thousand additional patients have been assessed in observational studies and in registries. Data from these studies have consistently demonstrated the safety and efficacy of CRT in patients with New York Heart Association class III and IV heart failure. Cardiac resynchronization therapy has been shown to significantly improve LV structure and function, New York Heart Association functional class, exercise tolerance, quality of life, and morbidity and mortality.

Pulsus alternans caused by 2:1 left bundle branch block

Pulsus alternans was caused by 2:1 left bundle branch block in a patient with a left ventricular ejection fraction of 50% and normal coronary arteries. The observations documented the profound depressant hemodynamic effect of complete left bundle branch block in the setting of minimal systolic left ventricular function.

Cardiac resynchronization therapy for the management of chronic heart failure

While numerous pathophysiologic mechanisms may lead to the onset and progression of chronic systolic heart failure, a variety of electrophysiologic abnormalities seen in the setting of chronic left ventricular dysfunction may also contribute to the natural history of the disease. Atrial, atrial-ventricular, and inter- and intraventricular conduction disturbances may place the failing ventricle at a further mechanical disadvantage, thus contributing to the functional impairment and poor outcomes associated with chronic heart failure. In the early 1990s, attempts at treating patients with end-stage systolic heart failure using conventional pacing strategies met with equivocal results. However, this work did provide further insight into the electromechanical consequences of advanced heart failure and suggested that atrial-synchronized biventricular pacing, or cardiac resynchronization therapy, might provide better and more consistent symptomatic and hemodynamic improvement. Several landmark clinical trials have evaluated the safety and efficacy of cardiac resynchronization therapy in New York Heart Association (NYHA) class III and IV heart failure. These studies have consistently shown statistically significant improvements in quality of life, NYHA functional class ranking, exercise tolerance, and left ventricular reverse remodeling. Some studies have suggested reductions in morbidity and mortality. This latter observation has been confirmed by a recent large-scale outcomes study. Thus, cardiac resynchronization therapy should be routinely considered in eligible NYHA class III and IV heart failure patients with ventricular dyssynchrony.

Radiofrequency catheter ablation of premature ventricular complexes from right ventricular outflow tract improves left ventricular dilation and clinical status in patients without structural heart disease

OBJECTIVES

The present study evaluated clinical benefits of radiofrequency catheter ablation (RFA) for premature ventricular complexes from right ventricular outflow tract (RVOT-PVC) in patients without structural heart disease.

BACKGROUND

It is unknown whether PVC causes left ventricular (LV) dilation, which is a well-recognized precursor of LV dysfunction and heart failure, and whether eliminating PVC by RFA produces clinical benefits in patients with RVOT-PVC.

METHODS

Frequency of PVC per total heart beats by 24-h Holter monitoring, left ventricular ejection fraction (LVEF), left ventricular end-diastolic internal dimension (LVDd), mitral regurgitation (MR) by echocardiogram, cardiothoracic ratio (CTR) by chest radiogram, and New York Heart Association (NYHA) functional class of 40 patients with RVOT-PVC without structural heart disease were evaluated before and 6 to 12 months after RFA.

RESULTS

Before RFA, a subgroup of patients with frequent (>20%) PVC demonstrated significantly enlarged LVDd and CTR, reduced LVEF, increased MR, and deteriorated NYHA functional class as compared to the subgroup with rare (<20%) PVC (54 +/- 1 mm vs. 45 +/- 1 mm, 52 +/- 2% vs. 46 +/- 1%, 66 +/- 2% vs. 73 +/- 2%, 1.2 +/- 0.2 degree vs. 0.4 +/- 0.1 degree, and 1.8 +/- 0.2 vs. 1.3 +/- 0.1, respectively; p < 0.05). Furthermore, ablating RVOT-PVC readily produced the improvement of all these abnormalities (47 +/- 1 mm, 41 +/- 1%, 72 +/- 2%, 0.3 +/- 0.1 degree, and 1.0 +/- 0.0, respectively; p < 0.05 compared with before RFA).

CONCLUSIONS

These findings suggest that frequent (>20%) RVOT-PVC may be a possible cause of LV dysfunction and/or heart failure, and RFA produces clinical benefits in these patients.

Left bundle branch block induces ventricular remodelling and functional septal hypoperfusion

AIMS

Left ventricular (LV) dilatation, hypertrophy, and septal perfusion defects are frequently observed in patients with left bundle branch block (LBBB). We investigated whether isolated LBBB causes these abnormalities.

METHODS AND RESULTS

In eight dogs, LBBB was induced by radio frequency ablation. Two-dimensional echocardiography showed that 16 weeks of LBBB decreased LV ejection fraction (by 23+/-14%) and increased LV cavity volume (by 25+/-19%) and wall mass (by 17+/-16%). The LV septal-to-lateral wall mass ratio decreased by 6+/-9%, indicating asymmetric hypertrophy. After onset of LBBB, myocardial blood flow (MBF, fluorescent microspheres) and systolic circumferential shortening [CS(sys), magnetic resonance (MR) tagging] decreased in the septum to 83+/-16% and -11+/-20% of baseline, respectively, and increased in LV lateral wall to 118+/-12% and 180+/-90% of baseline, respectively. MBF and CS(sys) values did not change over 16 weeks of LBBB. Changes in external mechanical work paralleled those in CS(sys). Glycogen content was not significantly different between septum and LV lateral wall of LBBB hearts (16 weeks) and control samples, indicating absence of hibernation.

CONCLUSIONS

The asynchronous ventricular activation during LBBB leads to redistribution of circumferential shortening and myocardial blood flow and, in the long run, LV remodelling. Septal hypoperfusion during LBBB appears to be primarily determined by reduced septal workload.

Robotic arrhythmia surgery and resynchronization

Over the last decade, significant technological advancements have occurred in cardiac surgery. One such breakthrough has been the use of robotic telemanipulation systems, which allow the surgeon to perform cardiac surgery through a minimally invasive approach. As a result, surgery for atrial fibrillation and resynchronization therapy for congestive heart failure have been increasingly incorporated into the surgeon's armamentarium.

Robotically assisted left ventricular epicardial lead implantation for biventricular pacing

OBJECTIVES

Ventricular resynchronization might be achieved in a minimally invasive fashion using a robotically assisted, direct left ventricular (LV) epicardial approach.

BACKGROUND

Approximately 10% of patients undergoing biventricular pacemaker insertion have a failure of coronary sinus (CS) cannulation. Rescue therapy for these patients currently is limited to standard open surgical techniques.

METHODS

Ten patients with congestive heart failure (New York Heart Association class 3.4 +/- 0.5) and a widened QRS complex (184 +/- 31 ms) underwent robotic LV lead placement after failed CS cannulation. Mean patient age was 71 +/- 12 years, LV ejection fraction (EF) was 12 +/- 6%, and LV end-diastolic diameter was 7.1 +/- 1.3 cm. Three patients had previous cardiac surgery, and five patients had a prior device implanted.

RESULTS

Nineteen epicardial leads were successfully placed on the posterobasal surface of the LV. Intraoperative lead threshold was 1.0 +/- 0.5 V at 0.5 ms, R-wave was 18.6 +/- 8.6 mV, and impedance was 1,143 +/- 261 ohms at 0.5 V. Complications included an intraoperative LV injury and a postoperative pneumonia. Improvements in exercise tolerance (8 of 10 patients), EF (19 +/- 13%, p = 0.04), and QRS duration (152 +/- 21 ms, p = 0.006) have been noted at three to six months follow-up. Lead thresholds have remained unchanged (2.1 +/- 1.4 V at 0.5 ms, p = NS), and a significant drop in impedance (310 +/- 59 ohms, p < 0.001) has been measured.

CONCLUSIONS

Robotic LV lead placement is an effective and novel technique which can be used for ventricular resynchronization therapy in patients with no other minimally invasive options for biventricular pacing.

Electrophysiological aids in congestive heart failure: supporting and synchronizing systole

Cardiac resynchronization therapy offers a new therapeutic approach for treating patients with ventricular dysynchrony and moderate to severe HF. Early experience suggests that it is safe and effective, with patients demonstrating significant improvement in both clinical symptoms as well as multiple measures of functional status and exercise capacity. Ongoing and future clinical trials should help to further validate the role of cardiac resynchronization in the treatment of patients with systolic HF.

Is the outcome of cardiac resynchronization therapy related to the underlying etiology?

This study was designed to examine the importance of the underlying cardiac pathology on outcome of cardiac resynchronization therapy (CRT), hypothesizing that myocardial infarction scar and other noncontractile segments represent limitations to the ability to resynchronize cardiac contraction in patients with congestive heart failure associated with dilated cardiomyopathy. From October 1999 to April 2002, 158 patients (mean age 65 years, 121 men) were included in a single center, longitudinal, comparative study. All patients had dilated cardiomyopathy and indications for CRT with a mean QRS duration of 174 ms. The patient population was divided into a coronary artery disease (CAD) group that included patients with significant CAD, and no indication, or a contraindication for revascularization, and a non-CAD group that included patients with nonischemic dilated cardiomypopathy. Follow-up data were collected at 3, 6, and 12 months, and yearly thereafter. The median follow-up was 11.2 months. In the CAD group, the LVEF increased from 0.29 to 0.34 (P < 0.0001), the 6-minute walk test distance increased from 310 to 463 m (P < 0.0001), and the percentage of patients in NYHA functional Class III-IV decreased from 83% to 23% (P = 0.04). In the non-CAD group, LVEF increased from 29% to 42% (P < 0.0001), the 6-minute walk test distance increased from 332 to 471 m (P < 0.0001), and the percentage of patients in NYHA functional Class III-IV decreased from 79% to 5%, (P < 0.0001). Comparison of the two groups showed that patients in the non-CAD group had a significantly greater increase in LVEF (P = 0.007) and decrease in NYHA class (P < 0.05). Patients with CAD or non-CAD significantly improved clinically during CRT. Non-CAD patients had a greater increase in LVEF and decrease in NYHA functional class than patients with CAD.

Relief of drug refractory angina by biventricular pacing in heart failure

Since cardiac resynchronization therapy (CRT) improves LV function at the cost of low energetic expenditure, the authors hypothesized that it may increase the threshold of drug refractory angina in selected patients with CHF and CAD who are not amenable to myocardial revascularization. From October 1999 to April 2002, 75 patients with CHF and CAD were treated with CRT. Drug refractory angina occurred nearly daily in 8 of the 75 patients. The mean age of these eight men was 71 years, mean NYHA functional Class 3.4 +/- 0.5, mean QRS duration (QRSd) 168 +/- 20 ms, and mean left ventricular ejection fraction (LVEF) 0.29 +/- 0.4. Diffuse CAD not amenable to myocardial revascularization was confirmed on angiography. At baseline, no patient was able to complete a 6-minute walk test because of angina. In the 6 months before CRT, the mean number of hospitalizations per patient for management of CHF or angina was 3.1 +/- 0.3. All patients underwent successful CRT. Mean QRSd decreased to 141 +/- 16 ms (P = 0.01 vs baseline). After 9 +/- 6.1 months, LVEF increased to 0.317 +/- 0.028 (P = 0.03 vs baseline), while the NYHA class decreased to 2.6 +/- 0.5 (P = 0.02 vs baseline). All patients also experienced a marked decrease in angina episodes, from a mean of 8.3 +/- 11.6 to 0.6 +/- 1.3 episodes/week (P < 0.05), and completed a 6-minute walk test, covering a mean distance of 337 +/- 68 m (vs 237 +/- 136 m at baseline, P = 0.007). No further hospitalization was necessary. The beneficial effects of CRT on overall cardiac function may include a better control of angina in severely symptomatic patients.

Cardiac resynchronization therapy for heart failure: biventricular pacing and beyond

In the early 1990s, attempts at treating patients with dilated cardiomyopathy and end-stage heart failure by using right-sided, dual-chamber pacing met with equivocal results. Although initially discouraging, this work did provide further insight into the electromechanical consequences of advanced heart failure and suggested that atrial-synchronized biventricular pacing, or cardiac resynchronization therapy, might provide better and more consistent symptomatic and hemodynamic improvement. Several studies have recently validated the safety and efficacy of cardiac resynchronization therapy in advanced heart failure. Data from these studies have shown statistically significant improvements in left ventricular ejection fraction, New York Heart Association class, exercise tolerance, and quality of life. Observed reductions in morbidity and mortality await confirmation from ongoing large-scale outcomes studies. This article reviews the evolution of pacing in heart failure and discusses the underlying mechanisms that are potentially responsible for the improvement seen in patients receiving cardiac resynchronization therapy. In addition, the results of recently completed clinical trials, as well as the status of ongoing clinical trials, are reviewed.

Cardiac resynchronization in chronic heart failure

BACKGROUND

Previous studies have suggested that cardiac resynchronization achieved through atrial-synchronized biventricular pacing produces clinical benefits in patients with heart failure who have an intraventricular conduction delay. We conducted a double-blind trial to evaluate this therapeutic approach.

METHODS

Four hundred fifty-three patients with moderate-to-severe symptoms of heart failure associated with an ejection fraction of 35 percent or less and a QRS interval of 130 msec or more were randomly assigned to a cardiac-resynchronization group (228 patients) or to a control group (225 patients) for six months, while conventional therapy for heart failure was maintained. The primary end points were the New York Heart Association functional class, quality of life, and the distance walked in six minutes.

RESULTS

As compared with the control group, patients assigned to cardiac resynchronization experienced an improvement in the distance walked in six minutes (+39 vs. +10 m, P=0.005), functional class (P<0.001), quality of life (-18.0 vs. -9.0 points, P= 0.001), time on the treadmill during exercise testing (+81 vs. +19 sec, P=0.001), and ejection fraction (+4.6 percent vs. -0.2 percent, P<0.001). In addition, fewer patients in the group assigned to cardiac resynchronization than control patients required hospitalization (8 percent vs. 15 percent) or intravenous medications (7 percent vs. 15 percent) for the treatment of heart failure (P<0.05 for both comparisons). Implantation of the device was unsuccessful in 8 percent of patients and was complicated by refractory hypotension, bradycardia, or asystole in four patients (two of whom died) and by perforation of the coronary sinus requiring pericardiocentesis in two others.

CONCLUSIONS

Cardiac resynchronization results in significant clinical improvement in patients who have moderate-to-severe heart failure and an intraventricular conduction delay.

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.