Right and Left Ventricular Activation Sequence in Patients with Heart Failure and Right Bundle Branch Block: A Detailed Analysis Using Three-Dimensional Non-Fluoroscopic Electroanatomic Mapping System

Effectiveness of Cardiac Resynchronization Therapy by QRS Morphology in the Multicenter Automatic Defibrillator Implantation Trial–Cardiac Resynchronization Therapy (MADIT-CRT)

Background—

This study aimed to determine whether QRS morphology identifies patients who benefit from cardiac resynchronization therapy with a defibrillator (CRT-D) and whether it influences the risk of primary and secondary end points in patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial–Cardiac Resynchronization Therapy (MADIT-CRT) trial.

Methods and Results—

Baseline 12-lead ECGs were evaluated with regard to QRS morphology. Heart failure event or death was the primary end point of the trial. Death, heart failure event, ventricular tachycardia, and ventricular fibrillation were secondary end points. Among 1817 patients with available sinus rhythm ECGs at baseline, there were 1281 (70%) with left bundle-branch block (LBBB), 228 (13%) with right bundle-branch block, and 308 (17%) with nonspecific intraventricular conduction disturbances. The latter 2 groups were defined as non-LBBB groups. Hazard ratios for the primary end point for comparisons of CRT-D patients versus patients who only received an implantable cardioverter defibrillator (ICD) were significantly ( P <0.001) lower in LBBB patients (0.47; P <0.001) than in non-LBBB patients (1.24; P =0.257). The risk of ventricular tachycardia, ventricular fibrillation, or death was decreased significantly in CRT-D patients with LBBB but not in non-LBBB patients. Echocardiographic parameters showed significantly ( P <0.001) greater reduction in left ventricular volumes and increase in ejection fraction with CRT-D in LBBB than in non-LBBB patients.

Conclusions—

Heart failure patients with New York Heart Association class I or II and ejection fraction ≤30% and LBBB derive substantial clinical benefit from CRT-D: a reduction in heart failure progression and a reduction in the risk of ventricular tachyarrhythmias. No clinical benefit was observed in patients with a non-LBBB QRS pattern (right bundle-branch block or intraventricular conduction disturbances).

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00180271.

Defining left bundle branch block in the era of cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) has emerged as an attractive intervention to improve left ventricular mechanical function by changing the sequence of electrical activation. Unfortunately, many patients receiving CRT do not benefit but are subjected to device complications and costs. Thus, there is a need for better selection criteria. Current criteria for CRT eligibility include a QRS duration ≥ 120 ms. However, QRS morphology is not considered, although it can indicate the cause of delayed conduction. Recent studies have suggested that only patients with left bundle branch block (LBBB) benefit from CRT, and not patients with right bundle branch block or nonspecific intraventricular conduction delay. The authors review the pathophysiologic and clinical evidence supporting why only patients with complete LBBB benefit from CRT. Furthermore, they review how the threshold of 120 ms to define LBBB was derived subjectively at a time when criteria for LBBB and right bundle branch block were mistakenly reversed. Three key studies over the past 65 years have suggested that 1/3 of patients diagnosed with LBBB by conventional electrocardiographic criteria may not have true complete LBBB, but likely have a combination of left ventricular hypertrophy and left anterior fascicular block. On the basis of additional insights from computer simulations, the investigators propose stricter criteria for complete LBBB that include a QRS duration ≥ 140 ms for men and ≥ 130 ms for women, along with mid-QRS notching or slurring in ≥ 2 contiguous leads. Further studies are needed to reinvestigate the electrocardiographic criteria for complete LBBB and the implications of these criteria for selecting patients for CRT.

Single-beat noninvasive imaging of ventricular endocardial and epicardial activation in patients undergoing CRT

Background

Little is known about the effect of cardiac resynchronization therapy (CRT) on endo- and epicardial ventricular activation. Noninvasive imaging of cardiac electrophysiology (NICE) is a novel imaging tool for visualization of both epi- and endocardial ventricular electrical activation.

Methodology/Principal Findings

NICE was performed in ten patients with congestive heart failure (CHF) undergoing CRT and in ten patients without structural heart disease (control group). NICE is a fusion of data from high-resolution ECG mapping with a model of the patient's individual cardiothoracic anatomy created from magnetic resonance imaging. Beat-to-beat endocardial and epicardial ventricular activation sequences were computed during native rhythm as well as during ventricular pacing using a bidomain theory-based heart model to solve the related inverse problem. During right ventricular (RV) pacing control patients showed a deterioration of the ventricular activation sequence similar to the intrinsic activation pattern of CHF patients. Left ventricular propagation velocities were significantly decreased in CHF patients as compared to the control group (1.6±0.4 versus 2.1±0.5 m/sec; p<0.05). CHF patients showed right-to-left septal activation with the latest activation epicardially in the lateral wall of the left ventricle. Biventricular pacing resulted in a resynchronization of the ventricular activation sequence and in a marked decrease of total LV activation duration as compared to intrinsic conduction and RV pacing (129±16 versus 157±28 and 173±25 ms; both p<0.05).

Conclusions/Significance

Endocardial and epicardial ventricular activation can be visualized noninvasively by NICE. Identification of individual ventricular activation properties may help identify responders to CRT and to further improve response to CRT by facilitating a patient-specific lead placement and device programming.

RV electrical activation in heart failure during right, left, and biventricular pacing

OBJECTIVES

To compare right ventricular (RV) activation during intrinsic conduction or pacing in heart failure (HF) patients.

BACKGROUND

RV activation during intrinsic conduction or pacing in patients with left ventricular (LV) dysfunction is unclear but may affect the prognosis. In cardiac resynchronization therapy (CRT), timed LV pacing (CRT-LV) may be superior to biventricular pacing (CRT-BiV), and is hypothesized to be due to the merging of LV-paced and right bundle branch-mediated wavefronts, thus avoiding perturbation of RV electrical activation.

METHODS

Epicardial RV activation duration (RVAD) (onset to end of free wall activation) was evaluated noninvasively by electrocardiographic imaging in healthy control subjects (n = 7) and compared with that of HF patients (LV ejection fraction 23 +/- 10%, n = 14). RVAD in HF was contrasted during RV pacing, CRT-BiV, and CRT-LV at optimized AV intervals.

RESULTS

During intrinsic conduction in HF (n = 12), the durations of QRS and precordial lead rS complexes were 158 +/- 24 and 77 +/- 17 ms, respectively, indicating delayed total ventricular depolarization but rapid initial myocardial activation. Echocardiography demonstrated no significant RV disease. RV epicardial voltage, activation patterns, and RVAD in HF did not differ from normal (RVAD 32 +/- 15 vs. 28 +/- 3 ms, respectively, p = 0.42). In HF, RV pacing generated variable areas of slow conduction and prolonged RVAD (78 +/- 33 ms, p < 0.001). RVAD remained delayed during CRT-BiV at optimized atrioventricular intervals (76 +/- 32 ms, p = 0.87). In contrast, CRT-LV reduced RVAD to 40 +/- 26 ms (p < 0.016), comparable to intrinsic conduction (p = 0.39) but not when atrioventricular conduction was poor or absent.

CONCLUSIONS

In HF patients without RV dysfunction treated with CRT, normal RV free wall activation in intrinsic rhythm indicated normal right bundle branch-mediated depolarization. However, the RV was vulnerable to the development of activation delays during RV pacing, whether alone or with CRT-BiV. These were avoided by CRT-LV in patients with normal atrioventricular conduction.

A left hemiblock improves cardiac resynchronization therapy outcomes in patients with a right bundle branch block

BACKGROUND

The current recommendation for cardiac resynchronization therapy (CRT) in congestive heart failure (CHF) patients is based on QRS duration, not on QRS morphology.

HYPOTHESIS

This study was performed to compare the effects of CRT in CHF patients with pure RBBB vs those with a coexisting left hemiblock (LHB). METHODS AND PATIENT POPULATION: A total of 271 consecutive patients who underwent CRT at Montefiore Medical Center were analyzed. Baseline ECGs were analyzed by 2 reviewers for RBBB and further classified into those with a coexisting LHB. Response to CRT was defined to be, at > or = 6 months after CRT, either an improvement in ejection fraction (EF) of at least 5%, or an improvement in New York Heart Association (NYHA) CHF class. A total of 44 patients were identified: 18 had pure RBBB and 26 had a coexisting LHB. The 2 groups were similar in respect to baseline characteristics (P > 0.05).

RESULTS

Only 4 out of 18 patients with pure RBBB compared to 18 out of 26 with LHB (P = 0.005) had an improvement in EF > or = 5%. The mean EF was - 1% in the pure RBBB group, but + 5.4% in those with LHB (P = 0.0031). Improvement in NYHA class was seen in 0 out of 18 with pure RBBB vs 7 out of 26 patients with LHB (P = 0.03).

CONCLUSION

If patients with RBBB also had LHB, their response to CRT was significantly better than if they had RBBB alone.

Mathematical models of the electrical action potential of Purkinje fibre cells

Early development of ionic models for cardiac myocytes, from the pioneering modification of the Hodgkin-Huxley giant squid axon model by Noble to the iconic DiFrancesco-Noble model integrating voltage-gated ionic currents, ion pumps and exchangers, Ca(2+) sequestration and Ca(2+)-induced Ca(2+) release, provided a general description for a mammalian Purkinje fibre (PF) and the framework for modern cardiac models. In the past two decades, development has focused on tissue-specific models with an emphasis on the sino-atrial (SA) node, atria and ventricles, while the PFs have largely been neglected. However, achieving the ultimate goal of creating a virtual human heart will require detailed models of all distinctive regions of the cardiac conduction system, including the PFs, which play an important role in conducting cardiac excitation and ensuring the synchronized timing and sequencing of ventricular contraction. In this paper, we present details of our newly developed model for the human PF cell including validation against experimental data. Ionic mechanisms underlying the heterogeneity between the PF and ventricular action potentials in humans and other species are analysed. The newly developed PF cell model adds a new member to the family of human cardiac cell models developed previously for the SA node, atrial and ventricular cells, which can be incorporated into an anatomical model of the human heart with details of its electrophysiological heterogeneity and anatomical complexity.

Left ventricular conduction delays and relation to QRS configuration in patients with left ventricular dysfunction

Left ventricular activation delay (LVAT) >100 ms may determine response to cardiac resynchronization therapy, but its prevalence and relation to QRS configuration are unknown. QRS duration and LVAT in control subjects (n = 30) were compared with those in patients with heart failure (HF; LV ejection fraction 23 +/- 8%, n = 120) with a QRS duration <120 ms (NQRS(HF), n = 35) or > or = 120 ms (left bundle branch block [LBBB(HF)], n = 54; right bundle branch block [RBBB(HF)], n = 31). LVAT was estimated by interval from QRS onset to basal inferolateral LV depolarization. In controls, QRS duration was 82 +/- 13 ms and LVAT was 55 +/- 18 ms. LVAT was always <100 ms. In patients with NQRS(HF), QRS duration (104 +/- 10 ms) and LVAT (82 +/- 22 ms) were prolonged versus controls (p <0.001). LVAT exceeded 100 ms in 8 of 35 patients. In patients with LBBB(HF), QRS duration (161 +/- 29 ms) and LVAT (136 +/- 33 ms) were prolonged compared with controls and patients with NQRS(HF) (p <0.001). LVAT exceeded 100 ms in 47 of 54 patients. In patients with RBBB(HF), QRS duration did not differ from that in patients with LBBB(HF), but LVAT (100 +/- 24 ms) was shorter (p <0.001). In 17 of 31 patients with RBBB(HF) LVAT was <100 ms (82 +/- 12), similar to those with NQRS(HF) (p = NS), indicating no LV conduction delay. However, in 7 of 31, LVAT (135 +/- 13 ms) was similar to that in patients with LBBB(HF) (p = NS). LVAT correlation with QRS duration varied (control p = 0.004, NQRS(HF) p = 0.15, RBBB(HF) p = 0.01, LBBB(HF) p <0.001). In conclusion, LV conduction delays in patients with HF varied with QRS configuration and duration, exceeding 100 ms in only 23% of patients with narrow QRS configuration and 45% with RBBB(HF) compared with 87% with LBBB(HF). Fewer than 25% of patients with RBBB(HF) demonstrated delays equivalent to those in patients with LBBB(HF.) These variations may affect efficacy to cardiac resynchronization therapy.

Influence of left ventricular lead location on outcomes in the COMPANION study

INTRODUCTION

There are no randomized controlled trial data that evaluate mortality and hospitalization rates in cardiac resynchronization therapy (CRT) recipients based on left ventricular (LV) lead location. We analyzed the event-driven outcomes of mortality and hospitalization as well as functional outcomes including Functional Class, Quality-of-Life, and 6-minute walk distance in 1,520 patients enrolled in the COMPANION study of CRT versus optimal medical therapy.

METHODS AND RESULTS

Over a mean follow-up after implantation of 16.2 months, patients randomized to CRT, regardless of lead location, experienced benefit compared with optimized pharmacologic therapy (OPT), with respect to all-cause mortality or heart failure hospitalization. All but a posterior location showed benefit with respect to the all-cause mortality or all-cause hospitalization outcome. Mortality benefit in CRT-D patients was indifferent to LV lead position. All functional outcomes including 6-minute walk distance, Quality-of-Life (QOL) and Functional Class improved with CRT, regardless of LV lead location.

CONCLUSION

LV lead location was not a major determinant of multiple measures of response to CRT therapy in the COMPANION Trial. While acute data indicate that a left lateral LV lead location results in the most favorable hemodynamic response, these chronic data suggest that positioning an LV lead in an anterior rather than a lateral or posterior LV location has similar benefit.

Usefulness of baseline electrocardiographic QRS complex pattern to predict response to cardiac resynchronization

Cardiac resynchronization therapy (CRT) improves morbidity and mortality in patients with heart failure with QRS>120 ms, yet most patients studied in clinical trials manifested baseline left branch bundle block (LBBB). It is unclear whether benefits of CRT extend to patients with right branch bundle block (RBBB) or a paced QRS at baseline despite QRS>120 ms. Orthotopic heart transplantation- and ventricular assist device-free survival, symptomatic response, and echocardiographic response were evaluated in the 636 patients who underwent CRT at our institution from 2000 to 2007 in whom the baseline electrocardiogram showed LBBB (n=412; 65%), paced QRS (n=162; 26%), or RBBB (n=62; 10%). Mortality was assessed using the Social Security Death Index, and the medical record was analyzed for clinical data. A decrease in New York Heart Association class>or=0.5 after >or=6 months of CRT defined symptomatic response. Echocardiographic evidence of improved left ventricular function and reverse remodeling was evaluated after >or=6 months of CRT. Survival free from orthotopic heart transplantation and ventricular assist device placement was best in patients with LBBB and worst in those with RBBB, whereas patients with paced QRS had an intermediate prognosis (p=0.003). This finding remained significant after controlling for baseline differences among the 3 groups. Symptomatic response was observed most often in patients with LBBB (60%), occurred least often in patients with RBBB (14%), and was intermediate in patients with paced QRS (46%; p<0.001). Echocardiographic improvement showed a similar stepwise trend. In conclusion, patients with RBBB undergoing CRT had low rates of symptomatic and echocardiographic response, and their survival free from orthotopic heart transplantation or ventricular assist device placement was significantly worse than in patients with LBBB. Patients with conventionally paced QRS experienced an intermediate response.

Effect of bundle branch block patterns on mortality in hospitalized patients with heart failure

A widened QRS interval is associated with increased mortality in patients with heart failure (HF). However, the prognostic significance of the type of bundle branch block (BBB) pattern in these patients is unclear. The data of 4,102 patients with HF hospitalized during a prospective national survey were analyzed to investigate the association between BBB type and 1-year mortality in 3,737 patients without pacemakers. Right BBB (RBBB) was present in 381 patients (10.2%) and left BBB (LBBB) in 504 patients (13.5%). RBBB and LBBB were associated with increased 1-year mortality on univariate analysis (odds ratio [OR] 1.44, 95% confidence interval [CI] 1.15 to 1.81, and OR 1.20, 95% CI 0.97 to 1.47, respectively). In patients with systolic HF, after adjusting for multiple risk factors, only RBBB was found to be an independent predictor of mortality (RBBB vs no BBB OR 1.62, 95% CI 1.12 to 2.33, and RBBB vs LBBB OR 1.71, 95% CI 1.09 to 2.69). This correlation was stronger in patients with lower left ventricular ejection fractions and was also maintained in patients without acute myocardial infarctions. Analyzing the data for all patients with HF, there was a trend for increased mortality in the RBBB group only (adjusted OR 1.21, 95% CI 0.94 to 1.56). LBBB was not related to mortality in patients with either systolic HF or preserved ejection fractions. In conclusion, RBBB rather than LBBB is an independent predictor of mortality in hospitalized patients with systolic HF. This prognostic marker could be used for risk stratification and the selection of treatment.

Diminished left ventricular dyssynchrony and impact of resynchronization in failing hearts with right versus left bundle branch block

OBJECTIVES

We compared mechanical dyssynchrony and the impact of cardiac resynchronization therapy (CRT) in failing hearts with a pure right (RBBB) versus left bundle branch block (LBBB).

BACKGROUND

Cardiac resynchronization therapy is effective for treating failing hearts with conduction delay and discoordinate contraction. Most data pertain to LBBB delays. With RBBB, the lateral wall contracts early so that biventricular (BiV) pre-excitation may not be needed. Furthermore, the magnitude of dyssynchrony and impact of CRT in pure RBBB versus LBBB remains largely unknown.

METHODS

Dogs with tachypacing-induced heart failure combined with right or left bundle branch radiofrequency ablation were studied. Basal dyssynchrony and effects of single and BiV CRT on left ventricular (LV) function were assessed by pressure-volume catheter and tagged magnetic resonance imaging, respectively.

RESULTS

Left bundle branch block and RBBB induced similar QRS widening, and LV function (ejection fraction, maximum time derivative of LV pressure [dP/dt(max)]) was similarly depressed in failing hearts with both conduction delays. Despite this, mechanical dyssynchrony was less in RBBB (circumferential uniformity ratio estimate [CURE] index: 0.80 +/- 0.03 vs. 0.58 +/- 0.09 for LBBB, p < 0.04; CURE 0-->1 is dyssynchronous-->synchronous). Cardiac resynchronization therapy had correspondingly less effect on hearts with RBBB than those with LBBB (i.e., 5.5 +/- 1.1% vs. 29.5 +/- 5.0% increase in dP/dt(max), p < 0.005), despite similar baselines. Furthermore, right ventricular-only pacing enhanced function and synchrony in RBBB as well or better than did BiV, whereas LV-only pacing worsened function.

CONCLUSIONS

Less mechanical dyssynchrony is induced by RBBB than LBBB in failing hearts, and the corresponding impact of CRT on the former is reduced. Right ventricular-only pacing may be equally efficacious as BiV CRT in hearts with pure right bundle branch conduction delay.

Modelling of the ventricular conduction system

The His-Purkinje conduction system initiates the normal excitation of the ventricles and is a major component of the specialized conduction system of the heart. Abnormalities and propagation blocks in the Purkinje system result in abnormal excitation of the heart. Experimental findings suggest that the Purkinje network plays an important role in ventricular tachycardia and fibrillation, which is the major cause of sudden cardiac death. Nowadays an important area in the study of cardiac arrhythmias is anatomically accurate modelling. The majority of current anatomical models have not included a description of the Purkinje network. As a consequence, these models cannot be used to study the important role of the Purkinje system in arrhythmia initiation and maintenance. In this article we provide an overview of previous work on modelling of the Purkinje system and report on the development of a His-Purkinje system for our human ventricular model. We use the model to simulate the normal activation pattern as well as abnormal activation patterns resulting from bundle branch block and bundle branch reentry.

Interventional electrophysiology and cardiac resynchronization therapy: delivering electrical therapies for heart failure

Implantable devices have become a readily available option for patients with heart failure. Not only do these patients develop bradycardia and ventricular tachycardia, but their ventricular dysfunction can often improve with cardiac resynchronization therapy. However, this is a complex and rapidly developing clinical science for which the physician chooses techniques and selects patients on the basis of the results of clinical trials, clinical experience, and rapidly evolving tools. The results depend on the interplay of these complex variables. Placement of the left ventricular lead has forced the device physician to develop new skills and/or interdisciplinary relationships with physicians with vascular intervention, imaging, and surgical skills. Familiarity with the cardiac venous anatomy, occlusive venography, venoplasty, guide wire tools, guiding catheters, stenting, and new intracardiac visualization and magnetic intracardiac lead positioning tools are examples of just a few of the novel skills that are useful in the delivery of cardiac resynchronization therapy. Beyond implantation, these patients and devices require specialized follow-up with continued medical therapy and echo-guided adjustments of device programming. Finally, there are ongoing controversies and many as yet unanswered questions that are the subject of ongoing and planned clinical trials.

Avoidance of Right Ventricular Pacing in Cardiac Resynchronization Therapy Improves Right Ventricular Hemodynamics in Heart Failure Patients

BACKGROUND

Cardiac resynchronization therapy (CRT) applied by pacing the left and right ventricles (BiV) has been shown to provide synchronous left ventricular (LV) contraction in heart failure patients. CRT may also be accomplished through synchronization of a properly timed LV pacing impulse with intrinsically conducted activation wave fronts. Elimination of right ventricular (RV) pacing may provide a more physiological RV contraction pattern and reduce device current drain. We evaluated the effects of LV and BiV pacing over a range of atrioventricular intervals on the performance of both ventricles.

METHODS

Acute LV and RV hemodynamic data from 17 patients with heart failure (EF = 30 +/- 1%) and a wide QRS (138 +/- 25 msec) or mechanical dyssynchrony were acquired during intrinsic rhythm, BiV, and LV pacing.

RESULTS

The highest LV dP/dt(max) was achieved during LV pre- (LV paced prior to an RV sense) and BiV pacing, followed by that obtained during LV post-pacing (LV paced after an RV sense) and the lowest LV dP/dt(max) was recorded during intrinsic rhythm. Compared with BiV pacing, LV pre-pacing significantly improved RV dP/dt(max) (378 +/- 136 mmHg/second vs 397 +/- 136 mmHg/second, P < 0.05) and preserved RV cycle efficiency (61.6 +/- 14.6% vs 68.6 +/- 11.4%, P < 0.05) and stroke volume (6.6 +/- 4.4 mL vs 9.0 +/- 6.3 mL, P < 0.05). Based on LV dP/dt(max), the optimal atrioventricular interval could be estimated by subtracting 30 msec from the intrinsic atrial to sensed RV interval.

CONCLUSIONS

Synchronized LV pacing produces acute LV and systemic hemodynamic benefits similar to BiV pacing. LV pacing at an appropriate atrioventricular interval prior to the RV sensed impulse provides superior RV hemodynamics compared with BiV pacing.

Identification of the Right Ventricular Pacing Site for Cardiac Resynchronization Therapy (CRT) Guided by Electroanatomical Mapping (CARTO)

BACKGROUND

The optimal left ventricle (LV) pacing site for cardiac resynchronization therapy (CRT) has been investigated, but less is known about the optimal site in the right ventricle (RV). The present study examined whether electrical resynchronization guided by electroanatomical mapping (CARTO) results in mechanical resynchronization.

METHODS AND RESULTS

The study group included 13 patients indicated for CRT: 10 with nonischemic cardiomyopathy, 2 with ischemic cardiomyopathy and 1 with cardiac sarcoidosis, (mean LV ejection fraction: 32+/-10%). CARTO of the RV septum was performed to identify the site with the most delayed conduction time during LV pacing. Hemodynamic measurements were performed during conventional biventricular pacing with the RV apex and LV (C-BVP) and during biventricular pacing with the most delayed site of the RV (d-RV) and LV (D-BVP). Lead placement at 15 coronary sinus veins was examined in the 13 patients. During pacing from anterolateral veins (n=2), the d-RV was the RV apex (RVA) in 1 patient and the mid-septum in the other. During pacing from lateral veins (n=9), the d-RV comprised the RVA (n=3), the mid-septum (n=5), and the right ventricular outflow tract (RVOT) (n=1). During pacing from the posterolateral veins (n=3), the d-RV was the RVOT in all cases. In 11 of 15 sites, d-RV differed from conventional RVA. Compared with C-BVP, D-BVP produced a significant improvement in LV dp/dt. Furthermore, RV mid-septum and LV pacing markedly increased LV dp/dt and pulse pressure (PP), but RVOT and LV pacing did not. D-BVP vs C-BVP: %LV dp/dt 30+/-20 and 15+/-15%, p<0.05; RV mid-septum and LV pacing vs C-BVP: %LV dp/dt 35+/-20 and 10+/-15%, p<0.02, and vs PP 33+/-20 and 10+/-29 mmHg, p<0.02.

CONCLUSIONS

For pacing from the LV lateral vein, potential improvement of cardiac performance compared with that by conventional RVA placement may be realized with concomitant pacing from the d-RV (mid-septum).

Right ventricular dyssynchrony in heart failure: a tissue Doppler imaging study

BACKGROUND

The development of right ventricular dysfunction is a poor prognostic sign in patients with heart failure (HF). Although left ventricular dyssynchrony has been well described, it is not known whether right ventricular dyssynchrony coexists in HF. We used tissue Doppler imaging to determine whether right ventricular dyssynchrony is also present in HF patients.

METHODS AND RESULTS

In 34 HF patients (mean age 56 +/- 13 years), we measured longitudinal strain at the right ventricular free wall, interventricular septum, and left ventricular lateral wall. Right ventricular and left ventricular dyssynchrony were defined as the difference in time to peak strain between the right ventricular free wall and the septum and between the left ventricular lateral wall and septum, respectively. Mean right ventricular dyssynchrony was 59 +/- 45 ms and the mean left ventricular dyssynchrony was 80 +/- 62 ms. We found a strong correlation between right ventricular dyssynchrony and pulmonary artery systolic pressure (r = 0.73; P < .001) and a negative correlation between right ventricular dyssynchrony and right ventricular fractional area change (r = -0.43; P < .02).

CONCLUSION

HF patients exhibit right ventricular dyssynchrony by strain imaging which correlates with pulmonary hypertension and right ventricular dysfunction.

Understanding nonresponders of cardiac resynchronization therapy--current and future perspectives

INTRODUCTION

Cardiac resynchronization therapy (CRT) is now an established nonpharmacologic therapy for advanced heart failure with electromechanical delay. Despite compelling evidence of the benefits of CRT, one troubling issue is the lack of a favorable response in about one-third of patients.

METHODS AND RESULTS

Currently, there is no unifying definition of responders, and published data were based on acute hemodynamic changes, chronic left ventricular reverse remodeling, as well as the intermediate or long-term clinical response. The lack of improvement with CRT can be due to many factors including the placement of the left ventricular pacing lead in an inappropriate location, the absence of electrical conduction delay or mechanical dyssynchrony despite wide QRS complexes, and possibly failure to optimize the CRT settings after device implantation. In acute hemodynamic studies, placing the left ventricular leads at the free wall region has been suggested to generate the best pulse pressure and positive dp/dt. The degree of mechanical dyssynchrony has recently been assessed noninvasively in CRT patients by echocardiography and in particular by tissue Doppler imaging. These studies suggested that responders of left ventricular reverse remodeling or systolic function had more severe systolic dyssynchrony. However, further studies are needed to examine the clinical utility of these parameters when applied to the standardized anatomic or functional endpoints. Optimization of atrioventricular and interventricular pacing intervals may also reduce the number of nonresponders, though newer methods, especially interventricular pacing intervals, are still under clinical investigation.

CONCLUSION

With the adjunctive use of imaging technology, physicians are able to characterize the response to CRT objectively, and cardiac imaging is an important clinical tool for determining more precisely the presence and degree of mechanical dyssynchrony.

Echocardiographic Assessment of Ventricular Asynchrony in Dilated Cardiomyopathy and Congenital Heart Disease: Tools and Hopes

Ventricular dyssynchrony is a relatively common problem in patients with heart failure, in particular those with wide QRS complex, and appears to have a deleterious effect on the natural history of heart failure, as it has been associated with increased mortality. Mechanistic studies, observational evaluations, and randomized trials have consistently demonstrated the beneficial effects of cardiac resynchronization therapy (CRT) in patients with moderate-to-severe chronic systolic heart failure and ventricular dyssynchrony who have failed optimal medical treatment. However, despite the promising results, it is estimated that in approximately 30% of patients undergoing CRT, the symptoms of heart failure do not improve or become even worse. One of the most important reasons for this failure is probably the lack of distinct mechanical dyssynchrony before implantation. A number of echocardiographic tools have been developed during the past 3 years for quantitative measurement of the severity of dyssynchrony before and after CRT. This review discusses the actual and potential role of different echocardiographic techniques in selection of patients and optimization of CRT and the value of some new clinical applications such as in congenital heart disease.

How many patients with heart failure are eligible for cardiac resynchronization? Insights from two prospective cohorts

AIMS

To determine what proportion of patients with heart failure are eligible for cardiac resynchronization therapy (CRT).

METHODS AND RESULTS

Eligibility criteria from the trials establishing the efficacy of CRT were applied to two prospective cohorts: the first enrolled patients with newly diagnosed heart failure discharged from 103 hospitals between April 1999 and March 2001 ('the hospital discharge cohort'); the second enrolled patients seen in a specialized clinic between August 2003 and January 2004 ('the specialty clinic cohort'). In the hospital discharge cohort, 73 patients (3% of the 2640 patients with ischaemic or dilated cardiomyopathy and 1% of all 9096 patients with heart failure discharged alive) met trial eligibility criteria: LVEF< or =0.35, QRS > or =120 ms, sinus rhythm, and NYHA class III or IV symptoms despite the treatment with ACE-inhibitor/angiotensin receptor blocker and beta-blocker. In the specialty clinic cohort, 54 patients (21% of the 263 patients with ischaemic or dilated cardiomyopathy and 17% of all 309 patients with heart failure) met these criteria. If persistent symptoms despite taking spironolactone were required for CRT eligibility, then the proportions qualifying dropped to 1% in the hospital discharge cohort and 18% in the specialty clinic cohort.

CONCLUSION

Few heart failure patients meet trial eligibility criteria for CRT.