Left ventricular or biventricular pacing improves cardiac function at diminished energy cost in patients with dilated cardiomyopathy and left bundle-branch block

Color Doppler tissue velocity imaging can disclose systolic left ventricular asynchrony independent of the QRS morphology in patients with severe heart failure

A QRS width greater than 120 ms is assumed to be a marker of inter- and intraventricular asynchrony in severe heart failure (HF) patients. Color Doppler tissue velocity imaging (c-TVI) with a time resolution of 10 ms was used to study regional left ventricular (LV) longitudinal systolic contraction pattern in HF patients with left and right bundle branch block (LBBB and RBBB) and in patients with normal QRS width. We studied 12 women and 23 men with severe HF, with a mean age of 66 +/- 11 years in New York Heart Association functional Class 2.9 +/- 0.6. Twenty patients had LBBB and 10 of those were accepted for cardiac resynchronization therapy by biventricular pacing (CRT). Ten patients had normal QRS width, and five had RBBB. In the echocardiographic apical four chamber view, regional peak LV tissue velocities and regional LV time differences of peak tissue velocities were compared at basal and mid-LV segments. There were no significant differences in regional mean peak tissue velocities among the patient groups. In patients with LBBB accepted for CRT, the LV lateral free-wall movement at basal LV was 29 ms delayed during main systole, almost significantly different from LBBB patients not accepted for CRT (P = 0.075). Even in HF patients with normal QRS width or RBBB, significant asynchronous longitudinal LV contraction was observed.

CONCLUSIONS

For the detection of regional longitudinal LV contraction asynchrony in patients with severe HF, supplementary methods to the surface ECG, such as c-TVI, are strongly recommended.

Assessment of right ventricular oxidative metabolism by PET in patients with idiopathic dilated cardiomyopathy undergoing cardiac resynchronisation therapy

PURPOSE

Right ventricular (RV) performance is known to have prognostic value in patients with congestive heart failure (CHF). Cardiac resynchronization therapy (CRT) has been found to enhance left ventricular (LV) energetics and metabolic reserve in patients with heart failure. The interplay between the LV and RV may play an important role in CRT response. The purpose of the study was to investigate RV oxidative metabolism, metabolic reserve and the effects of CRT in patients with CHF and left bundle brach block. In addition, the role of the RV in the response to CRT was evaluated.

METHODS

Ten patients with idiopathic dilated cardiomyopathy who had undergone implantation of a biventricular pacemaker 8+/-5 months earlier were studied under two conditions: CRT ON and after CRT had been switched OFF for 24 h. Oxidative metabolism was measured using [11C]acetate positron emission tomography (Kmono). The measurements were performed at rest and during dobutamine-induced stress (5 microg/kg per minute). LV performance and interventricular mechanical delay (interventricular asynchrony) were measured using echocardiography.

RESULTS

CRT had no effect on RV Kmono at rest (ON: 0.052+/-0.014, OFF: 0.047+/-0.018, NS). Dobutamine-induced stress increased RV Kmono significantly under both conditions but oxidative metabolism was more enhanced when CRT was ON (0.076+/-0.026 vs 0.065+/-0.027, p=0.003). CRT shortened interventricular delay significantly (45+/-33 vs 19+/-35 ms, p=0.05). In five patients the response to CRT was striking (32% increase in mean LV stroke volume, range 18-36%), while in the other five patients no response was observed (mean change +2%, range -6% to +4%). RV Kmono and LV stroke volume response to CRT correlated inversely (r=-0.66, p=0.034). None of the other measured parameters, including all LV parameters and electromechanical parameters, were associated with the response to CRT. In responders, RV Kmono with CRT OFF was significantly lower than in non-responders (0.036+/-0.01 vs 0.058+/-0.02, p=0.047).

CONCLUSION

CRT appears to enhance RV oxidative metabolism and metabolic reserve during stress. Patients responding to CRT appear to have lower RV oxidative metabolism at rest, suggesting that the RV plays a significant role in the response to CRT.

Load dependence of cardiac output in biventricular pacing: right ventricular pressure overload in pigs

BACKGROUND

The effect of biventricular pacing on stroke volume is believed to be dependent on right ventricular/left ventricular delay, but effects in individual patients are unpredictable. This variability may reflect relative right and left ventricular volume and/or pressure overloads. Accordingly, we tested the hypothesis that the relation of cardiac output to right ventricular/left ventricular delay is load dependent in a pig model of pulmonary stenosis.

METHODS

After median sternotomy in 6 anesthetized, domestic pigs, complete heart block was induced by ethanol ablation. During epicardial, atrial tracking DDD biventricular pacing, atrioventricular delay was varied between 60 and 180 ms in 30-ms increments. Right ventricular/left ventricular delay was varied at each atrioventricular delay from +80 ms (right ventricle first) to -80 ms (left ventricle first) in 20-ms increments. Aortic flow, right ventricular pressure, peripheral arterial pressure, and electrocardiogram were measured in the control state and during pulmonary stenosis, created by tightening a snare around the pulmonary artery until cardiac output decreased by 50%.

RESULTS

Atrioventricular and right ventricular/left ventricular delay had no effect on cardiac output during the control state, but during pulmonary stenosis there was a statistically significant (P =.0001, repeated-measures analysis of variance) right ventricular/left ventricular delay-related trend toward higher cardiac output with right ventricular pacing first. This effect was more pronounced when the optimal atrioventricular delay was determined first, resulting in a 20% increase in cardiac output when the optimal right ventricular/left ventricular delay was compared with simultaneous biventricular pacing.

CONCLUSIONS

Optimized biventricular pacing in swine is associated with increased cardiac output during acute pulmonary stenosis, but not during the control state. Further studies are needed to determine whether specific types of right ventricular and left ventricular overload predictably affect the relation between right ventricular/left ventricular delay and cardiac output.

Device therapy for the management of advanced heart failure

Rapid advances have been made over the last decade in the nonpharmacological treatment of patients with advanced heart failure. This article reviews the current application of device therapy including cardiac resynchronization, defibrillators, cardiac restraint devices and mechanical ventricular support in patients with advanced heart failure.

Load dependence of cardiac output in biventricular pacing: Right ventricular volume overload in pigs

BACKGROUND

Previous work from our laboratory has demonstrated that optimization of biventricular pacing is load dependent. During acute pulmonary stenosis and right ventricular pressure overload in swine, cardiac output was maximized by pacing the right ventricle 40 ms before the left ventricle. To extend those studies, this experiment examined biventricular pacing optimization during right ventricular volume overload.

METHODS

After median sternotomy in 6 anesthetized domestic pigs, complete heart block was induced by ethanol ablation. A conduit was grafted from the right ventricle to the right atrium to simulate tricuspid insufficiency. During epicardial, atrial tracking DDD biventricular pacing, atrioventricular delay was varied between 60 and 180 ms in 30-ms increments. Right ventricular-left ventricular delay was varied at each atrioventricular delay from +80 ms (right ventricle first) to -80 ms (left ventricle first) in 20-ms increments. Aortic flow, right ventricular pressure, and electrocardiogram were measured at each pacemaker setting with the graft clamped and unclamped.

RESULTS

Atrioventricular and right ventricular-left ventricular delays had no significant effect on cardiac output with the graft clamped. With the graft unclamped, however, there was a statistically significant (P =.003 by mixed modeling repeated measures analysis of variance) trend toward higher cardiac output with left ventricle-first pacing.

CONCLUSION

Left ventricle-first biventricular pacing in swine significantly increased cardiac output during acute tricuspid insufficiency but not during the control state. Trials are warranted to develop clinical biventricular pacing for treatment of perioperative right ventricular dysfunction.

Cardiac Resynchronization Therapy

Heart failure is a major health problem in the United States, associated with high morbidity, mortality, and economic burden. Despite recent advances in pharmacological treatments to attenuate disease progression, medications become relatively ineffective, resulting in worsening congestive symptoms and increased exercise intolerance. Cardiac resynchronization therapy provides a new adjunct for heart failure patients who remain symptomatic despite optimized medical therapies. This article discusses cardiac resynchronization therapy and measures that should be considered to ensure proper functioning of the device and improved quality of life for patients.

Catecholamines restore myocardial contractility in dilated cardiomyopathy at the expense of increased coronary blood flow and myocardial oxygen consumption (MvO2cost of catecholamines in heart failure)

To investigate the metabolic cost of catecholamine use in heart failure, we administered intravenous dobutamine or norepinephrine to dogs with moderate and severe LV dysfunction until LV contractile function was restored to normal levels. Both drugs were associated with significant increases in myocardial O(2) consumption, increased coronary blood flow requirements and decreased myocardial mechanical efficiency. These mechanisms may contribute to the deleterious effects of catecholamines in heart failure.

Relation of right ventricular pacing in tetralogy of Fallot to electrical resynchronization

Prolonged QRS duration is a marker of increased sudden death risk in tetralogy of Fallot. Right ventricular pacing increased QRS duration in this population and could be counteracted with optimization of the atrioventricular interval in a subset of patients, potentially offering right ventricular resynchronization in patients with baseline right bundle branch block. Effective pacing therapy may require site-specific placement of pacing leads and precise pacemaker programming.

Ventricular Activation Onset-Triggered Left Ventricular Pacing:. Safety and Feasibility in Initial Clinical Experience

Ventricular activation onset-triggered (VAOT) left ventricular pacing modalities synchronize left ventricular paced activation with existing intrinsic ventricular activation, in patients with complete LBBB and adequate rate. The purpose of this study was to evaluate the safety and feasibility of VAOT pacing with one left ventricular pacing lead, during temporary pacing in the postoperative period following open heart surgery. VAOT pacing was studied in five patients with LBBB and two patients with previously implanted right ventricular pacemakers. The VAOT pacing system used was assembled by modifying the function of existing equipment and its programming is described in detail. Comparative ECGs are reported, documenting the changes in ventricular activation produced by VAOT pacing. Stability of surface ECG acquisition was found to be essential to the success of temporary VAOT pacing and inappropriate pacing due to ECG instability is described. Patients were studied at rest and none experienced congestive heart failure. In the comparison of cardiac output, with and without VAOT pacing, no significant differences were found in LBBB patients or those with right ventricular pacemakers. In the comparison of arterial pressure, with and without VAOT pacing, no significant differences were found in six patients, however, in one LBBB patient with intrinsic predominant ventricular trigeminy, VAOT pacing was observed to have an antiarrhythmic effect resulting in suppression of ventricular ectopy and stabilization of arterial pressure. All patients survived VAOT pacing and the postoperative period without complications requiring additional intervention or treatment.

The Left Ventricular Apex is the Optimal Site for Pediatric Pacing:. Correlation with Animal Experience

Pacing at the commonly used right ventricular (RV) apex results in impaired ventricular performance. Previous animal studies indicated that the left ventricular (LV) apex is a superior pacing site. The purpose of this study was to investigate in dogs whether this good performance is associated with a more synchronous electrical activation pattern of the LV and whether the LV apex is also a good pacing site in children. In 11 healthy dogs and 8 children undergoing cardiac surgery, dual chamber pacing was performed at the RV apex, LV apex and LV lateral free wall (LVFW). In dogs, a basket electrode was inserted into the LV to assess pattern and timing of LV endocardial activation. In the children, hemodynamic measurements were performed immediately after recovery from cardiopulmonary bypass. In dogs, LV apex pacing resulted in synchronous activation around the LV circumference whereas RV apex and LVFW pacing resulted in asynchrony of activation between the septum and LVFW. In both canine and children's hearts most hemodynamic variables remained at sinus rhythm level during LV apex pacing, but LVdPdtmax, stroke work (dogs), and pulse pressure (children) were reduced as compared with sinus rhythm during RV apex and LVFW pacing. LV apex pacing results in synchronous activation of the LV and is, in adult dogs and in children, associated with superior hemodynamic performance.

Cardiac-resynchronization therapy with or without an implantable defibrillator in advanced chronic heart failure

BACKGROUND

We tested the hypothesis that prophylactic cardiac-resynchronization therapy in the form of biventricular stimulation with a pacemaker with or without a defibrillator would reduce the risk of death and hospitalization among patients with advanced chronic heart failure and intraventricular conduction delays.

METHODS

A total of 1520 patients who had advanced heart failure (New York Heart Association class III or IV) due to ischemic or nonischemic cardiomyopathies and a QRS interval of at least 120 msec were randomly assigned in a 1:2:2 ratio to receive optimal pharmacologic therapy (diuretics, angiotensin-converting-enzyme inhibitors, beta-blockers, and spironolactone) alone or in combination with cardiac-resynchronization therapy with either a pacemaker or a pacemaker-defibrillator. The primary composite end point was the time to death from or hospitalization for any cause.

RESULTS

As compared with optimal pharmacologic therapy alone, cardiac-resynchronization therapy with a pacemaker decreased the risk of the primary end point (hazard ratio, 0.81; P=0.014), as did cardiac-resynchronization therapy with a pacemaker-defibrillator (hazard ratio, 0.80; P=0.01). The risk of the combined end point of death from or hospitalization for heart failure was reduced by 34 percent in the pacemaker group (P<0.002) and by 40 percent in the pacemaker-defibrillator group (P<0.001 for the comparison with the pharmacologic-therapy group). A pacemaker reduced the risk of the secondary end point of death from any cause by 24 percent (P=0.059), and a pacemaker-defibrillator reduced the risk by 36 percent (P=0.003).

CONCLUSIONS

In patients with advanced heart failure and a prolonged QRS interval, cardiac-resynchronization therapy decreases the combined risk of death from any cause or first hospitalization and, when combined with an implantable defibrillator, significantly reduces mortality.

Cardiac Resynchronization Therapy:. Device-Based Medicine for Heart Failure

Cardiac resynchronization therapy (CRT) or biventricular pacing is a novel adjunctive therapy for patients with advanced heart failure (HF). Many patients with severe HF have a left bundle branch block or an intraventricular conduction delay, with up to 25% of patients with a QRS > 120 ms, resulting in significant left ventricular (LV) dyssynchrony and a high mortality rate. The efficacy of CRT is based on the reduction in the conduction delay between the two ventricles and optimization of the ejection fraction, decrement in mitral regurgitation, LV remodeling, thus resulting in symptom improvement. Cardiac resynchronization therapy can be achieved both transvenously using a coronary sinus branch, or epicardially. Clinical trials have demonstrated a significant improvement in the NYHA class and the exercise capacity as well as a marked reduction in the hospitalization rate. More recently, the COMPANION trial showed a 43% reduction in a composite endpoint of all-cause mortality and hospitalization in the group receiving a CRT device in combination with an implantable cardiac defibrillator (ICD). Thus, management of patients with reduced LV function, wide QRS, and symptomatic refractory HF, despite optimal drug therapy, should include CRT as an option. The adjunct of an ICD combined with CRT should be considered if the LV ejection fraction (ischemic cardiomyopathy) is <30%. There are still significant unanswered questions regarding the nonresponder population and the role of tissue Doppler imaging techniques, the impact of CRT on total mortality and CRT in dilated cardiomyopathy or chronic atrial fibrillation. The use CRT postoperatively or at time of cardiac surgery, as well as new epicardial approaches using a thoracoscopic approach or robotically assisted surgery in patients not suitable for coronary vein leads are challenging topics to address in the years to come.

Cardiac resynchronization by pacing: an electrical treatment of heart failure

Various modalities of cardiac pacing have been proposed in the past to improve hemodynamics, either directly or indirectly. Some of these are conventional ways of cardiac stimulation, others such as biventricular or left ventricular pacing, represent dedicated pacing techniques. Left ventricular and biventricular pacing are successfully applied in those patients with congestive heart failure who have conduction disturbances (i.e. left bundle branch block) as they correct the ensuing intra- and interventricular dyssynchrony. This is the reason why these pacing modalities are described as cardiac resynchronization therapy. According to the results of a series of studies, the cardiac resynchronization therapy seems to have a favourable clinical impact in terms of quality of life, morbidity and hospitalization rate. On-going and future studies should assess the impact of resynchronization therapy on overall mortality and its cost-effectiveness profile in specific subgroups of patients. Other open issues regard (i) the convenience of using biventricular pacing as a pacing-alone therapy or in combination with ventricular defibrillation capability, especially for potential candidates to heart transplantation, and (ii) the ways to identify properly the responders to resynchronization therapy.

Cardiac resynchronization therapy—How big of a miracle?

This review examines the clinical benefit of cardiac resynchronization therapy (CRT) in patients with severe heart failure symptoms and interventricular conduction delay. The magnitude of CRT effects on exercise duration, quality of life, and reversal of adverse remodeling are compared to angiotensin-converting enzyme (ACE) inhibitor therapy and combined beta-blocker/ACE inhibitor therapy. Overall, CRT delivers substantial improvement in clinical well-being to an extent similar to or greater than what would be expected with neurohormonal intervention alone.

Biventricular pacing in heart failure

Optimal pharmacological therapy for heart failure improves patients' prognosis and symptoms. Despite this, the long-term prognosis for these patients is very poor and symptoms are debilitating. Biventricular pacing, or resynchronization therapy, should be considered for patients who remain symptomatic despite optimal therapy and have evidence of dyssynchrony.

The effects of cardiac resynchronization therapy on left ventricular function, myocardial energetics, and metabolic reserve in patients with dilated cardiomyopathy and heart failure

OBJECTIVES

The effects of long-term cardiac resynchronization therapy (CRT) on left ventricular (LV) energetics and metabolic reserve were evaluated.

BACKGROUND

Cardiac resynchronization therapy is a new therapy for patients with drug-refractory severe heart failure (HF).

METHODS

Ten patients with idiopathic dilated cardiomyopathy who had undergone implantation of biventricular pacemaker 8 +/- 5 months earlier were studied during two conditions: CRT switched on, and after CRT was switched off for 24 h. Left ventricular function was measured using echocardiography and oxidative metabolism using [(11)C]acetate positron emission tomography. Both measurements were performed at rest and during dobutamine-induced stress (5 microg/kg/min). Basal- and adenosine-stimulated (140 microg/kg/min) myocardial blood flow were quantitated using [(15)O]water.

RESULTS

During CRT off, LV stroke volume was significantly reduced at rest (72 +/- 18 ml vs. 63 +/- 15 ml, p < 0.05), but LV oxidative metabolism (K(mono)) remained unchanged (0.046 +/- 0.008 vs. 0.054 +/- 0.016 min(-1)) leading to a significant deterioration of myocardial efficiency of forward work (from 48.2 +/- 16.7 to 36.6 +/- 11.7 mm Hg.l/g, p < 0.05). During dobutamine-induced stress, stroke volume and K(mono) values were not different whether CRT was on or off. However, myocardial efficiency (56.1 +/- 16.1 vs. 49.8 +/- 18.0 mm Hg.ml.g(-1).min(-1), p = 0.099) and metabolic reserve, the response of K(mono) to dobutamine (0.023 +/- 0.014 vs. 0.013 +/- 0.014 min(-1), p = 0.09), tended to reduce when CRT was switched off. Cardiac resynchronization therapy had no effects on myocardial perfusion. Natriuretic peptides increased significantly during CRT-off period.

CONCLUSIONS

Long-term CRT has beneficial effects on LV function and myocardial efficiency at rest in patients with HF. These effects are not associated with changes in myocardial perfusion or oxygen consumption. During dobutamine-induced stress, CRT does not affect functional parameters, but myocardial efficiency and metabolic reserve may be increased.

Relationship between regional shortening and asynchronous electrical activation in a three-dimensional model of ventricular electromechanics

INTRODUCTION

Asynchronous electrical activation can cause abnormalities in perfusion and pump function. An electromechanical model was used to investigate the mechanical effects of altered cardiac activation sequence.

METHODS AND RESULTS

We used an anatomically detailed three-dimensional computational model of the canine ventricular walls to investigate the relationship between regional electrical activation and the timing of fiber shortening during normal and ventricular paced beats. By including a simplified Purkinje fiber network and anisotropic impulse conduction in the model, computed electrical activation sequences were consistent with experimentally observed patterns. Asynchronous time courses of regional strains during beats stimulated from the left or right ventricular epicardium showed good agreement with published experimental measurements in dogs using magnetic resonance imaging tagging methods. When electrical depolarization in the model was coupled to the onset of local contractile tension development by a constant time delay of 8 msec, the mean delay from depolarization to the onset of systolic fiber shortening was 14 msec. However, the delay between the onset of fiber tension and initial shortening varied significantly; it was as late as 60 msec in some regions but was also as early as -50 msec (i.e., 42 msec before depolarization) in other regions, particularly the interventricular septum during free-wall pacing.

CONCLUSION

The large variation in delay times was attributable to several factors including local anatomic variations, the location of the site relative to the activation wavefront, and regional end-diastolic strain. Therefore, we conclude that these factors, which are intrinsic to three-dimensional ventricular function, make the regional sequence of fiber shortening an unreliable surrogate for regional depolarization or electromechanical activation in the intact ventricles.

Effects of cardiac resynchronization therapy on myocardial blood flow measured by oxygen-15 water positron emission tomography in idiopathic-dilated cardiomyopathy and left bundle branch block

Regional and global myocardial blood flow and coronary vascular resistance were determined in patients with idiopathic-dilated cardiomyopathy and left bundle branch block before and during cardiac resynchronization therapy (CRT) using oxygen-15 water positron emission tomography. The investigated parameters did not exhibit regional heterogeneity and were not influenced by CRT. This implies that the beneficial effects of CRT do not require additional oxygen demand or regional reallocation of oxidative metabolism.

Current status of cardiac resynchronization therapy

PURPOSE OF REVIEW

Cardiac resynchronization therapy with biventricular pacing has rapidly emerged as an indispensable treatment option in patients with moderate-to-advanced heart failure and left bundle branch block. New findings on the pathophysiology of cardiac resynchronization therapy and its clinical effects are reviewed.

RECENT FINDINGS

Several randomized trials have evaluated the effects of cardiac resynchronization therapy on cardiac haemodynamics and clinical parameters in selected heart failure patients with left bundle branch block. The effects of cardiac resynchronization therapy on mechanical synchrony have been evaluated by different imaging modalities, such as echocardiography and radionuclide angiography. Cardiac resynchronization therapy leads to improved haemodynamics at a diminished energy cost, and improves functional mitral regurgitation. This haemodynamic improvement is associated with a significantly better quality of life, improved exercise capacity, and less frequent hospitalization. Recent preliminary data suggest a positive effect on cardiac mortality. However, approximately a third of implanted patients do not benefit from cardiac resynchronization therapy, and therefore additional criteria for the identification of mechanical dyssynchrony are needed to identify those patients who will respond before implantation.

SUMMARY

Many randomized trials have confirmed the benefits of cardiac resynchronization therapy in selected heart failure patients. The successful resynchronization of the ventricular activation-contraction sequence is the major determinant of acute haemodynamic and long-term clinical improvement. The diagnostic sensitivity and specificity of the non-invasive identification of mechanical dyssynchrony may be improved by echocardiography, but further research is needed to identify the optimal strategy for patient identification.

Non-contact left ventricular endocardial mapping in cardiac resynchronisation therapy

BACKGROUND

Up to 30% of patients with heart failure do not respond to cardiac resynchronisation therapy (CRT). This may reflect placement of the coronary sinus lead in regions of slow conduction despite optimal positioning on current criteria.

OBJECTIVES

To characterise the effect of CRT on left ventricular activation using non-contact mapping and to examine the electrophysiological factors influencing optimal left ventricular lead placement.

METHODS

and results: 10 patients implanted with biventricular pacemakers were studied. In six, the coronary sinus lead was found to be positioned in a region of slow conduction with an average conduction velocity of 0.4 m/s, v 1.8 m/s in normal regions (p < 0.02). Biventricular pacing with the left ventricle paced 32 ms before the right induced the optimal mean velocity time integral and timing for fusion of depolarisation wavefronts from the right and left ventricular pacing sites. Pacing outside regions of slow conduction decreased left ventricular activation time and increased cardiac output and dP/dt(max) significantly.

CONCLUSIONS

In patients undergoing CRT for heart failure, non-contact mapping can identify regions of slow conduction. Significant haemodynamic improvements can occur when the site of left ventricular pacing is outside these slow conduction areas. Failure of CRT to produce clinical benefits may reflect left ventricular lead placement in regions of slow conduction which can be overcome by pacing in more normally activating regions.

Timing of cardiac contraction in humans mapped by high-temporal-resolution MRI tagging: early onset and late peak of shortening in lateral wall

Mechanical asynchrony is an important parameter in predicting the response to cardiac resynchronization therapy, but detailed knowledge of cardiac contraction timing in healthy persons is scarce. In this work, timing of cardiac contraction was mapped in 17 healthy subjects with high-temporal-resolution (14 ms) MRI myocardial tagging and strain analysis. Both the onset time of circumferential shortening (T(onset)) in early systole and the time of peak circumferential shortening (T(peak)) at end systole were determined. The onset of shortening width (time needed for 20-90% of the left ventricle to start shortening) was small (35 +/- 9 ms). A distinct spatial pattern for T(onset) was found, with earliest onset in the lateral wall and latest onset in the septum (P = 0.001). Compared with T(onset), T(peak) had a larger width (121 +/- 22 ms) and an opposite spatial pattern, with peak shortening occurring earlier in the septum than in the lateral wall (P < 0.001). Postsystolic shortening (T(peak) later than aortic valve closure; P < 0.05) was observed in 13 of the 30 cardiac segments, mainly in the lateral and basal segments. Shortening in these segments continued 58 +/- 14 ms after aortic valve closure, during which circumferential shortening increased from 16.9 +/- 1.2% to 20.0 +/- 1.5%. Maps of the timing of contraction in normal subjects may serve as a reference in detecting mechanical asynchrony due to intraventricular conduction defects or ischemia.

Clinical efficacy of cardiac resynchronization therapy using left ventricular pacing in heart failure patients stratified by severity of ventricular conduction delay

OBJECTIVES

We assessed the clinical efficacy of single-site left ventricular (LV) pacing and determined the impact of baseline conduction delay severity on the magnitude of benefit.

BACKGROUND

Multisite biventricular pacing can improve heart failure (HF) symptoms in patients with an intraventricular conduction delay by resynchronizing abnormal ventricular contractions and improving LV systolic function.

METHODS

Eighty-six patients with at least New York Heart Association functional class II HF, chronic LV systolic dysfunction, normal sinus rhythm, and a QRS interval over 120 ms were implanted for atrial-synchronized LV pacing. The single-blinded, randomized, controlled, crossover study stratified patients 1:1 by the baseline QRS interval into long (QRS >150 ms) and short (QRS 120 to 150 ms) groups, which were compared during a three-month period of active (univentricular) pacing and a three-month period of inactive (ventricular inhibited) pacing. The primary end point was peak oxygen consumption (VO(2)) followed by anaerobic threshold, distance walked in 6 min, and quality-of-life questionnaire score.

PATIENTS

Twelve patients were withdrawn before randomization and 17 could not complete both study periods. The short QRS group did not improve in any end point with active pacing. For the long QRS group, peak VO(2) increased 2.46 ml/min/kg (p < 0.001), the anaerobic threshold increased 1.55 ml/min/kg (p < 0.001), the distance walked in 6 min increased 47 m (p = 0.024), and the quality-of-life score improved 8.1 points (p = 0.004).

CONCLUSIONS

Left ventricular pacing significantly improves exercise tolerance and quality of life in patients with chronic HF, LV systolic dysfunction, and a QRS interval over 150 ms.

Advances in devices for cardiac resynchronization in heart failure

Patients with advanced heart failure have a high mortality and morbidity despite medical therapy. Depending on the underlying heart disease and severity of heart failure, 3.7 to 52.8% of patients have a QRS complex > or =120 ms who may have interventricular and intraventricular dyssynchrony correctible by cardiac resynchronization therapy (CRT). The latter is usually achieved with biventricular pacing, with the left ventricular lead placed in a tributary of the coronary sinus (CS), with a reported success rate between 88-92%. The technical advances for implantation include preformed guide sheaths to cannulate the CS, over the wire leads with passive fixation mechanism, and surgical placement methods. Device-specific CRT features include optimizing heart failure through insurance of a high percentage of pacing, heart failure monitoring, atrioventricular and interventricular timing, and avoiding double ventricular sensing. Furthermore, arrhythmic co-morbidities of heart failure such as atrial fibrillation and ventricular tachyarrhythmias can also be managed. Recent prospective trials suggest that there is a 30% reduction in heart failure hospitalization with CRT, and preliminary results suggest a survival benefit with CRT and implantable cardioverter defibrillator over optimal medical therapy.

Pacing follow up techniques and trouble shooting during biventricular pacing

Cardiac resynchronization has proven to be a useful adjunct therapy for heart failure patients with ventricular conduction disturbances. However, new issues have emerged including the follow-up and trouble-shooting of the biventricular devices. Peri-implant and immediate post-implant follow-up is necessary if procedure-related complications are to be revealed and proper system functioning ensured. Additionally, during the long-term follow-up the optimum device functioning should be evaluated, as should the patient's clinical and functional improvement. Finally, trouble-shooting resulting from the use of biventricular devices is another matter that needs to be addressed and physicians active in the field should continually upgrade their knowledge in the constantly evolving technologies of cardiac resynchronizers.

Intra-left ventricular electromechanical asynchrony

OBJECTIVES

We sought to assess the electromechanical parameters, using tissue Doppler echocardiography, as potential independent predictors of heart failure (HF) worsening.

BACKGROUND

Ventricular conduction disorders worsen the prognosis for HF patients. However, the relationships between the QRS width and morphology, hemodynamic parameters, and presence and magnitude of intra-left ventricular (LV) and inter-ventricular (V) asynchrony have not been well clarified.

METHOD

A total of 104 patients with an LV ejection fraction (EF) </=45% and stabilized HF, without myocardial infarction (MI), underwent echocardiography coupled with tissue Doppler imaging and were followed for one year. The protocol analyzed the incidence of worsening HF (hospitalization for cardiac decompensation). Inter-V and regional electromechanical delays for the anterior, septal, inferior, and lateral LV walls were correlated with the QRS morphology and duration. The intra-LV and inter-V asynchrony values of these patients were compared with those of healthy subjects matched by gender and age criteria to determine the respective normal ranges.

RESULTS

The presence of intra-LV (but not inter-V) asynchrony was identified as an independent predictor of severe cardiac events (hazard ratio 3.39, p < 0.0001), independent of the LVEF and QRS width. Of patients with a QRS width <120 ms (55%; n = 57), 56% presented with major intra-LV asynchrony and 12% with inter-V asynchrony. Intra-LV asynchrony was observed in 84% of left bundle branch block patients, but also in 83% of right bundle branch block patients (p = NS). There was a poor correlation between the QRS width and intra-LV or inter-V asynchrony (r = 0.36, p = NS and r = 0.43, p = 0.05, respectively).

CONCLUSIONS

In HF patients without MI, patients with intra-LV asynchrony are those with a significantly higher risk of cardiac events, independent of the QRS width and LVEF. Accordingly, such patients should be more actively identified for early intensive treatment and survey.

Effect of Cardiac Resynchronization Therapy on Left Atrial Reverse Remodeling and Spontaneous Echo Contrast

Recent studies revealed reverse remodeling in left ventricle with cardiac resynchronization therapy (CRT). However, effects on left atrial remodeling, left atrial total emptying fraction and left atrial spontaneous echo contrast (SEC) have not been adequately evaluated. The aim of this study was to investigate the long-term changes in SEC, left atrial reverse remodeling, and left atrial total emptying fraction after CRT. Twenty patients with systolic heart failure and complete left bundle-branch block underwent implantation of biventricular pacemaker devices. Transthoracic and transesophageal echocardiography were performed one week before and one and six months after pacemaker implantation. After biventricular pacemaker implantation, significant clinical improvement was observed in all patients. Left atrial maximal and minimal volumes showed a significant progressive decline after CRT (reverse remodeling). Left atrial total emptying ejection fraction (LATEF) was 33 +/- 19% at baseline and increased to 37 +/- 10% and 41 +/- 11% at the 1st and 6th months respectively (p = 0.01 and p = 0.04). SEC was detected in 18 of 20 patients (90%) at the beginning of the study. After six months SEC disappeared in 5 patients and frequency of SEC reduced to 45%. Decrease in the intensity of the SEC was also statistically significant (at the 1st and 6th months; p = 0.001 and p < 0.001 respectively). Long-term CRT results in atrial reverse remodeling, increases LATEF, and reduces both frequency and intensity of atrial SEC.

Acute comparative effect of right and left ventricular pacing in patients with permanent atrial fibrillation

We tested the hypothesis that left ventricular (LV) pacing is superior to right ventricular (RV) apical pacing in patients undergoing atrioventricular (AV) junction ablation and pacing for permanent atrial fibrillation. The potential benefit of LV over RV pacing needs to be evaluated without the confounding effect of other variables that can influence cardiac performance. An acute intrapatient comparison of the QRS width and echocardiographic parameters between RV versus LV pacing was performed within 24 h after ablation in 44 patients. Both modes of pacing were also compared with pre-implantation values. Compared with RV pacing, LV pacing caused a 5.7% increase in the ejection fraction (EF) and a 16.7% decrease in the mitral regurgitation (MR) score; the QRS width was 4.8% shorter with LV pacing. Similar results were observed in patients with or without systolic dysfunction and/or native left bundle branch block, except for a greater improvement in MR in the latter group. Compared with pre-ablation measures, the EF increased by 11.2% and 17.6% with RV and LV pacing, respectively; the MR score decreased by 0% and 16.7%; and the diastolic filling time increased by 12.7% and 15.6%.Rhythm regularization achieved with AV junction ablation improved EF with both RV and LV pacing; LV pacing provided an additional modest but favorable hemodynamic effect, as reflected by a further increase of EF and reduction of MR. The effect seems to be equal in patients with both depressed and preserved systolic functions and in those with and without native left bundle branch block.

Potential Candidates for Cardiac Resynchronization Therapy in Japanese Patients With Idiopathic Dilated Cardiomyopathy-A Niigata Multicenter Study of DCM-

BACKGROUND

The purpose of this study was to assess the candidates suitable for cardiac resynchronization therapy (CRT) and to examine the significance of the QRS duration in Japanese patients with idiopathic dilated cardiomyopathy (DCM).

METHODS AND RESULTS

The study population consisted of 357 patients. The selection criteria for candidates suitable for CRT were QRS duration =130 ms, left ventricular ejection fraction (LVEF) =35% and New York Heart Association (NYHA) functional class III or IV by ACC/AHA/NASPE 2002 guidelines. We divided the study population into 2 groups: group A with a QRS duration <130 ms, and group B with a QRS duration =130 ms. In 25 of the 375 patients (7.0%), all the criteria were fulfilled. Group B had a significantly larger left ventricular diameter end-diastole and end-systole than group A (P<0.0001). Group B had a lower LVEF (P<0.0001). There was a fair inverse correlation (r=-0.58, P<0.0001) between the length of the QRS duration and LVEF.

CONCLUSION

Approximately 7% of the Japanese patients with DCM are CRT candidates. In the present study, we found that prolonged QRS duration was associated with poor systolic function.

Biventricular mechanical asynchrony predicts hemodynamic effect of uni- and biventricular pacing

We tested whether biventricular resynchronization explains contractile function changes with univentricular and biventricular pacing in heart failure patients with varying magnitudes of baseline biventricular asynchrony. Thirty patients (New York Hospital Association class ≥ III, QRS duration ≥120 ms) were tested. Contractile function was measured by left ventricular maximum first derivative of pressure over time (dP/d tmax). Biventricular mechanical asynchrony was quantified by the normalized pressure-pressure (NPP) loop area formed by the cross-plot of right and left intraventricular pressure curves from each cardiac cycle. Any ventricular pacing increased dP/d tmax if it decreased baseline NPP loop area and almost always worsened dP/d tmax and asynchrony when baseline NPP loop area <0.3. The quantitative relationship between dP/d tmax and NPP loop area change depended on ventricular pacing site and timing relative to intrinsic activation. For similar NPP loop decreases, dP/d tmax increased 16% more with left and biventricular pacing compared with right ventricular pacing. In conclusion, right, left, or biventricular pacing can improve contractile function only in patients having sufficient baseline biventricular asynchrony. However, biventricular resynchronization is only one of the improvement mechanisms.

Window to the heart: the value of a native and paced QRS duration. Current perspective and review

Given the technological advances and reliance upon expensive testing for guiding therapy, it is surprising how an inexpensive, low tech electrocardiogram can provide a wealth of information pertaining to the underlying cardiovascular status of a patient. In this article we review the changes in hemodynamics, prognosis and guidance of therapeutic options associated with a prolonged QRS duration.

Transvenous Biventricular Pacing in a Child after Congenital Heart Surgery as an Alternative Therapy for Congestive Heart Failure

Transvenous Biventricular Pacing in Children. Cardiac resynchronization therapy improves short-term and long-term hemodynamics in adult patients with congestive heart failure and left bundle branch block. We describe the feasibility of transvenous biventricular pacemaker implantation in a 6-year-old child with heart failure and wide QRS complex after congenital heart surgery. Myocardial tissue Doppler imaging was used to demonstrate intraventricular dyssynchrony and resynchronization after cardiac resynchronization therapy. During 1-year follow-up, symptomatology and hemodynamic parameters improved.

Cardiac resynchronization therapy is an important advance in the management of congestive heart failure

Cardiac resynchronization therapy (CRT) is an emerging therapy that improves symptoms and exercise tolerance in patients with advanced heart failure, left ventricular systolic dysfunction, and intraventricular conduction delay. By correcting the AV, interventricular, and intraventricular dyssynchrony induced by conduction disorders, controlled studies have shown that CRT improved functional status, decreased heart failure hospitalization rate, and might have a positive effect on left ventricular remodeling. Recent and preliminary data from the COMPANION trial suggest that CRT alone or in association with defibrillator capacity significantly reduced total mortality and hospitalization and that total mortality was significantly reduced only in the CRT plus implantable cardioverter defibrillator (ICD) group. Many questions remain unanswered, particularly the selection of responder patients.

Cardiac resynchronization therapy can reverse abnormal myocardial strain distribution in patients with heart failure and left bundle branch block

OBJECTIVES

We studied the effects of cardiac resynchronization therapy (CRT) on regional myocardial strain distribution, as determined by echocardiographic strain rate (SR) imaging.

BACKGROUND

Dilated hearts with left bundle branch block (LBBB) have an abnormal redistribution of myocardial fiber strain. The effects of CRT on such abnormal strain patterns are unknown.

METHODS

We studied 18 patients (12 males and 6 females; mean age 65 +/- 11 years [range 33 to 76 years]) with symptomatic systolic heart failure and LBBB. Doppler myocardial imaging studies were performed to acquire regional longitudinal systolic velocity (cm/s), systolic SR (s(-1)), and systolic strain (%) data from the basal and mid-segments of the septum and lateral wall before and after CRT. By convention, negative SR and strain values indicate longitudinal shortening.

RESULTS

Before CRT, mid-septal peak SR and peak strain were lower than in the mid-lateral wall (peak SR: -0.79 +/- 0.5 [septum] vs. -1.35 +/- 0.8 [lateral wall], p < 0.05; peak strain: -7 +/- 5 [septum] vs. -11 +/- 5 [lateral wall], p < 0.05). This relationship was reversed during CRT (peak SR: -1.35 +/- 0.8 [septum] vs. -0.93 +/- 0.6 [lateral wall], p < 0.05; peak strain: -11 +/- 6 [septum] vs. -7 +/- 6 [lateral wall], p < 0.05). Cardiac resynchronization therapy reversed the septal-lateral difference in mid-segmental peak strain from -46 +/- 94 ms (LBBB) to 17 +/- 92 ms (CRT; p < 0.05).

CONCLUSIONS

Left bundle branch block can lead to a significant redistribution of abnormal myocardial fiber strains. These abnormal changes in the extent and timing of septal-lateral strain relationships can be reversed by CRT. The noninvasive identification of specific abnormal but reversible strain patterns should help to improve patient selection for CRT.

Intra-ventricular resynchronization for optimal left ventricular function during pacing in experimental left bundle branch block

OBJECTIVES

We sought to investigate to what extent intra-ventricular asynchrony (intraVA) and inter-ventricular asynchrony (interVA) determine left ventricular (LV) function in canine hearts with left bundle branch block (LBBB) during ventricular pacing.

BACKGROUND

Pacing therapy improves LV pump function in patients with heart failure and abnormal ventricular conduction supposedly due to resynchronization. However, the relationship between LV pump function and measures of asynchrony is not well established.

METHODS

In 15 experiments, LV (various sites) and biventricular (BiV) pacing was performed at atrioventricular (AV) delays of 20 to 140 ms. Measured were the maximum rate of increase (dP/dt(max)) of LV pressure and LV stroke work (SW) (conductance catheter), interVA (time delay between the upslope of LV and RV pressures), and intraVA (from endocardial electrical activation maps).

RESULTS

Induction of LBBB increased interVA (-6.4 +/- 8.6 to -28.4 +/- 8.5 ms [RV earlier]) and intraVA (4.9 +/- 2.4 to 18.0 +/- 3.3 ms), whereas LV dP/dt(max) and SW decreased (-13 +/- 18% and -39 +/- 24%, respectively). During LBBB, LV and BiV pacing increased LV dP/dt(max) and SW (mean increases 14% to 21% and 11% to 15%, respectively) without changing diastolic function or preload. Optimal improvement in LV function was obtained consistently when intraVA returned to pre-LBBB values, while interVA remained elevated. Normalization of intraVA required AV delays shorter than the baseline PQ time during LV apex and BiV pacing, thus excluding endogenous LV activation, but AV delays virtually equal to the baseline PQ time (difference 4 +/- 9 ms, p = NS) during pacing at (mid)lateral LV sites to obtain fusion between pacing-induced and endogenous activation.

CONCLUSIONS

In LBBB hearts, optimal restoration of LV systolic function by pacing requires intra-ventricular resynchronization. The optimal AV delay to achieve this depends on both the site of pacing and baseline PQ time.

Cardiac Resynchronization Therapy for Advanced Heart Failure

Cardiac resynchronization therapy (CRT) represents a new class of heart failure therapy that provides symptom relief and decreased need of hospitalization in a significant number of patients already receiving maximal medical intervention. Patients with ischemic or nonischemic dilated cardiomyopathy, coupled with interventricular conduction delays, who have New York Heart Association class III or IV symptoms, are currently candidates for CRT. This device-based intervention reverses adverse ventricular remodeling, decreases the severity of mitral regurgitation, and increases cardiac efficiency and output. New selection criteria are being considered in an attempt to identify patients who have a high chance of responding, and possibly, to identify patients that have a high chance of not responding to CRT. These efforts are in response to the 20% to 25% "nonresponder" rate observed when the currently accepted inclusion criteria are used. Other patient populations may also benefit from CRT, including those in need of antibradycardia pacing, patients with atrial fibrillation, and some who meet the criteria for prophylactic implantation of a cardiac defibrillator. This review focuses on the current strategies to refine patient selection criteria and addresses some of the practical issues in prescribing CRT.

Colour tissue velocity imaging can show resynchronisation of longitudinal left ventricular contraction pattern by biventricular pacing in patients with severe heart failure

OBJECTIVE

To quantify ventricular resynchronisation by biventricular pacing using colour tissue Doppler velocity imaging (c-TVI).

DESIGN AND PATIENTS

c-TVI shows regional tissue velocity profiles with a very high time resolution (10 ms). Eighteen patients were studied from an apical four chamber view at baseline and after a one month follow up of biventricular pacing. Regional left ventricular peak tissue velocities and regional time differences during the cardiac cycle were compared in the basal and mid interventricular septal segments of the left ventricle, and in the corresponding segments in the left ventricular free wall.

RESULTS

From baseline to follow up, mean peak tissue velocities changed only during isovolumic contraction in the basal interventricular septum and the left ventricular free wall. At baseline the peak main systolic tissue velocities in the left ventricular free wall were typically delayed by an average of 42 ms in the basal left ventricular site and by 14 ms in the mid left ventricular site compared with the corresponding sites in the interventricular septum. After resynchronisation by biventricular pacing those regional movements were separated by an average of only 7 ms at the basal site, but there was still a 21 ms earlier movement of the left ventricular free wall in the mid left ventricular site. The diastolic movement pattern remained unchanged from baseline to follow up.

CONCLUSIONS

c-TVI showed a significant asynchronous regional longitudinal movement of basal left ventricular sites at baseline. A change to a more synchronous longitudinal left ventricular movement pattern during biventricular pacing was demonstrated.

Cardiac resynchronization therapy: overcoming ventricular dyssynchrony in dilated heart failure

Despite optimal medical therapy, dilated heart failure is associated with a dismal prognosis and relentless progression. Intraventricular conduction delay or bundle branch block is a marker of heart failure progression and worsening prognosis. Patients fitting this profile have been shown to benefit from a specific form of cardiac pacing now referred to as cardiac resynchronization therapy (CRT). This monograph is an in-depth review of the theory and consequences of ventricular dyssynchrony in dilated heart failure, and provides an overview of the major clinical trials of CRT. Practical considerations for achieving ventricular resynchronization are discussed, with an emphasis on biventricular pacing.

Left ventricular mechanics and myocardial blood flow following restoration of normal activation sequence in paced patients with long-term right ventricular apical stimulation

STUDY OBJECTIVES

Asynchronous ventricular activation, as induced by ventricular pacing, is known to affect left ventricular (LV) systolic and diastolic function and myocardial blood flow. However, it is not clear whether the long-term disturbances it causes are reversible after the restoration of the normal ventricular activation sequence.

DESIGN

In this study, we used the conductance catheter method and a Doppler guidewire to assess the changes in LV mechanics, and correspondingly in myocardial blood flow, after the restoration of the normal ventricular activation sequence in patients with long-term right ventricular apical pacing.

PATIENTS

Sixteen patients (mean [+/- SD] age, 61 +/- 11 years; 9 men) with right ventricular apical stimulation and complete ventricular pacing capture for a very long period were studied. In eight patients, we analyzed pressure-volume loops before and immediately after the restoration of the normal ventricular activation sequence, and in the remaining eight patients the myocardial blood flow and flow reserve were analyzed.

MEASUREMENTS AND RESULTS

End-systolic elastance (Ees) [5.503 +/- 0.6 vs 4.287 +/- 0.28 mm Hg/mL, respectively; p = 0.003] and its ratio to effective arterial elastance (1.63 +/- 0.51 vs 2.00 +/- 0.64, respectively; p = 0.009), which are indexes of systolic function and ventriculoarterial coupling, respectively, improved significantly after restoration of the normal ventricular activation sequence. Indexes of diastolic function and the predicted myocardial oxygen consumption (MO(2)) showed no clear change. Coronary flow in the dominant coronary artery increased significantly (46.55 +/- 14.12 vs 71.55 +/- 27.53 mL/min, respectively; p = 0.002), while the coronary flow reserve in the same artery decreased (3.5 +/- 1.0 vs 2.6 +/- 0.5, respectively; p = 0.008).

CONCLUSIONS

The restoration of a normal activation sequence after long-term ventricular asynchrony enhances acutely contractile function without affecting MO(2). These changes in LV function do not appear to have causal relationships with myocardial blood flow changes.

Acute hemodynamic benefit of multisite ventricular pacing after congenital heart surgery

BACKGROUND

Cardiac dysfunction after congenital heart surgery is a major cause of morbidity and mortality. Cardiac resynchronization through multisite ventricular pacing (MSVP) improves cardiac index and ventricular function, and lowers systemic vascular resistance (SVR) in adults with heart failure and interventricular conduction delay.

METHODS

The acute hemodynamic effects of MSVP after congenital heart surgery were assessed. Twenty-nine patients (aged 1 week to 17 years) with prolonged QRS interval had atrial and ventricular unipolar epicardial temporary pacing leads placed at surgery. Group 1 consisted of patients with a single ventricle (n = 14); group 2 included patients with two-ventricle anatomy (tetralogy of Fallot, ventricular septal defect) undergoing ventricular surgery (n = 10); and group 3 included patients with two-ventricle anatomy undergoing other cardiac surgery (n = 5). At a mean postoperative day 1 (range, 0 to 6), blood pressure, systemic and mixed venous oxygen saturations, electrocardiograms, and echocardiograms were obtained before and after 20 minutes of MSVP.

RESULTS

The QRS duration decreased with MSVP in all patients (mean, 23%, p < 0.005). Systolic blood pressure improved in all patients (mean, 9.7%, p < 0.005). Cardiac index improved in 19 of 21 patients tested, with no change in 2 patients (mean, 15.1%, p = 0.0001). In 2 patients, MSVP facilitated weaning from cardiopulmonary bypass. Echocardiographic mitral or tricuspid valve inflow was not significantly different with MSVP.

CONCLUSIONS

Multisite ventricular pacing results in improved cardiac index and increased systolic blood pressure, and it can also facilitate weaning from cardiopulmonary bypass. Multisite ventricular pacing may be used as adjunct to standard postoperative treatment of cardiac dysfunction after congenital heart surgery.

New pacing technologies for heart failure

Heart failure is a sizeable problem in elderly populations, and although pharmacological treatment has improved, outcome generally remains poor. New pacing technologies have been developed to treat heart failure, with promising results

Combining electrical therapies for advanced heart failure: the Milan experience with biventricular pacing-defibrillation backup combination for primary prevention of sudden cardiac death

Biventricular pacing (BVP) improves hemodynamics and symptoms in patients with heart failure with bundle branch block. Patients with a left ventricular ejection fraction <0.35 and ventricular tachyarrhythmias are at risk of sudden cardiac death, and they benefit most from implantable cardioverter defibrillators (ICDs). No study has evaluated the efficacy of the BVP-ICD combination in patients with heart failure with no history of syncope or sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Our prospective, observational study was performed on 135 consecutive patients with heart failure (aged, 64 +/- 11 years; 76% male; New York Heart Association functional class, 3.1 +/- 0.8; ejection fraction 0.28 +/- 0.06; ischemic heart failure, 43%; QRS interval duration, 153 +/- 11 msec) treated at our cardiac pacing unit between January 1999 and April 2001. In the first year (control phase), BVP alone was implanted. After that, BVP with ICD backup was used (prophylactic phase). Follow-up data were obtained by outpatient visits with electrocardiographic and echocardiographic examinations done at 3-month intervals. For patients who died, we examined hospital records, death certificates, and autopsy reports. Follow-up time averaged 840 days. The first 47 patients received BVP alone. During follow-up study, 19% of these patients died suddenly, and 11% died of worsening heart failure. None of the patients who died suddenly had hemodynamic deterioration or BVP malfunction before the event. The BVP-ICD group comprised 88 patients (18% with VT/VF inducibility on electrophysiologic testing). During follow-up study, 32% of these patients (18% with positive electrophysiologic testing) had VT/VF episodes successfully treated by ICD; 5% received inappropriate discharges on atrial fibrillation; and 6% died of heart failure with 1 sudden cardiac death. Cox proportional hazards model in the BVP-ICD group compared with BVP alone revealed hazard ratios for all-cause mortality and sudden cardiac death of 0.76 (95% confidence interval [CI], 0.58 to 0.96; p = 0.01) and 0.08 (95% CI, 0.05 to 0.42; p <0.01), respectively, adjusting for baseline characteristics and follow-up duration. Mortality in patients with heart failure remains high after BVP implantation, mainly because of sudden cardiac death. Although there are limitations with an observational study, our experience suggests that ICD backup grants increased security in BVP patients without conventional class I ICD indications.

Cardiac resynchronization therapy homogenizes myocardial glucose metabolism and perfusion in dilated cardiomyopathy and left bundle branch block

OBJECTIVES

We investigated whether cardiac resynchronization therapy (CRT) affects myocardial glucose metabolism and perfusion in dilated cardiomyopathy (DCM) and left bundle branch block (LBBB).

BACKGROUND

Patients with DCM and LBBB present with asynchronous left ventricular (LV) activation, leading to reduced septal glucose metabolism. Cardiac resynchronization therapy recoordinates LV activation, but its effects on myocardial glucose metabolism and perfusion remain unknown.

METHODS

In 15 patients (10 females; 61 +/- 13 years) with DCM and LBBB (QRS width 165 +/- 15 ms), gated (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) and technetium-99m ((99m)Tc)-sestamibi single-photon emission computed tomography were performed before and after two weeks of CRT. Uptake of FDG and (99m)Tc-sestamibi was determined in four LV wall areas. Ejection fraction and volumes were calculated from gated PET.

RESULTS

Baseline FDG uptake was heterogeneous (p < 0.0001), with lowest uptake in the septal region (56 +/- 12%) and highest uptake in the lateral region (89 +/- 6%). During CRT, septal and anterior increases (p < 0.01) and lateral decreases (p < 0.01) resulted in homogeneously distributed glucose metabolism. Baseline heterogeneity (p < 0.0001) in (99m)Tc-sestamibi uptake was modest (lowest septal 65 +/- 10%; maximum lateral 84 +/- 5%) and also reduced with CRT, although some heterogeneity (p < 0.05) remained. The septal-to-lateral ratio increased with CRT for FDG (0.62 +/- 0.12 to 0.91 +/- 0.26, p < 0.001) and (99m)Tc-sestamibi uptake (0.77 +/- 0.13 to 0.85 +/- 0.16, p < 0.01). The LV end-diastolic and end-systolic volumes decreased from 293 +/- 160 to 272 +/- 158 ml (p < 0.05) and from 244 +/- 164 to 220 +/- 160 ml (p < 0.01), respectively. Ejection fraction increased from 22 +/- 12% to 25 +/- 13% (p < 0.01).

CONCLUSIONS

Glucose metabolism is reduced more than perfusion in the septal compared with LV lateral wall in patients with DCM and LBBB. Cardiac resynchronization therapy restores homogeneous myocardial glucose metabolism with less influence on perfusion.

Novel technique for cardiac electromechanical mapping with magnetic resonance imaging tagging and an epicardial electrode sock

Near-simultaneous measurements of electrical and mechanical activation over the entire ventricular surface are now possible using magnetic resonance imaging tagging and a multielectrode epicardial sock. This new electromechanical mapping technique is demonstrated in the ventricularly paced canine heart. A 128-electrode epicardial sock and pacing electrodes were placed on the hearts of four anesthetized dogs. In the magnetic resonance scanner, tagged cine images (8-15 ms/frame) and sock electrode recordings (1000 Hz) were acquired under right-ventricular pacing and temporally referenced to the pacing stimulus. Electrical recordings were obtained during intermittent breaks in image acquisition, so that both data sets represented the same physiologic state. Since the electrodes were not visible in the images, electrode recordings and cine images were spatially registered with Gd-DTPA markers attached to the sock. Circumferential strain was calculated at locations corresponding to electrodes. For each electrode location, electrical and mechanical activation times were calculated and relationships between the two activation patterns were demonstrated. This method holds promise for improving understanding of the relationships between the patterns of electrical activation and contraction in the heart.