Beneficial effects of biventricular pacing in patients with a "narrow" QRS

Contemporary Review of Left Bundle Branch Block in the Failing Heart - Pathogenesis, Prognosis, and Therapy

Cardiac resynchronisation therapy (CRT) is a cornerstone in the contemporary management of heart failure. The most effective way of predicting response to this therapy remains electrocardiographic (ECG) criteria of electromechanical dyssynchrony. The left bundle branch block (LBBB) pattern is currently the most robust ECG criterion in predicting improvement in symptoms and reduction in mortality. However, recent studies using three-dimensional (3D) mapping and cardiac magnetic resonance imaging (CMR) have demonstrated heterogeneous left ventricular activation patterns in patients with LBBB. This has led to intense debate on the activation pattern of "true LBBB" and resulted in the proposal of stricter criteria for defining LBBB. This review will focus on the definitions and implications of LBBB in the CRT era. At a minimum, the use of stricter ECG criteria appears warranted, and adjunctive pre-implant imaging or mapping may further identify patient-specific electrophysiological patterns that determine response to CRT.

Multipoint Pacing versus conventional ICD in Patients with a Narrow QRS complex (MPP Narrow QRS trial): study protocol for a pilot randomized controlled trial

BACKGROUND

Despite an intensive search for predictors of the response to cardiac resynchronization therapy (CRT), the QRS duration remains the simplest and most robust predictor of a positive response. QRS duration of ≥ 130 ms is considered to be a prerequisite for CRT; however, some studies have shown that CRT may also be effective in heart failure (HF) patients with a narrow QRS (<130 ms). Since CRT can now be performed by pacing the left ventricle from multiple vectors via a single quadripolar lead, it is possible that multipoint pacing (MPP) might be effective in HF patients with a narrow QRS. This article reports the design of the MPP Narrow QRS trial, a prospective, randomized, multicenter, controlled feasibility study to investigate the efficacy of MPP using two LV pacing vectors in patients with a narrow QRS complex (100-130 ms).

METHODS

Fifty patients with a standard ICD indication will be enrolled and randomized (1:1) to either an MPP group or a Standard ICD group. All patients will undergo a low-dose dobutamine stress echo test and only those with contractile reserve will be included in the study and randomized. The primary endpoint will be the percentage of patients in each group that have reverse remodeling at 12 months, defined as a reduction in left ventricular end-systolic volume (LVESV) of >15% from the baseline.

DISCUSSION

This feasibility study will determine whether MPP improves reverse remodeling, as compared with standard ICD, in HF patients who have a narrow QRS complex (100-130 ms).

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02402816 . Registered on 25 March 2015.

Prevalence, correlates, and prognostic significance of QRS prolongation in heart failure with reduced and preserved ejection fraction

AIMS

The independent clinical correlates and prognostic impact of QRS prolongation in heart failure (HF) with reduced and preserved ejection fraction (EF) are poorly understood. The rationale for cardiac resynchronization therapy (CRT) in preserved EF is unknown. The aim was to determine the prevalence of, correlates with, and prognostic impact of QRS prolongation in HF with reduced and preserved EF.

METHODS AND RESULTS

We studied 25,171 patients (age 74.6 ± 12.0 years, 39.9% women) in the Swedish Heart Failure Registry. We assessed QRS width and 40 other clinically relevant variables. Correlates with QRS width were assessed with multivariable logistic regression, and the association between QRS width and all-cause mortality with multivariable Cox regression. Pre-specified subgroup analyses by EF were performed. Thirty-one per cent had QRS ≥120 ms. Strong predictors of QRS ≥120 ms were higher age, male gender, dilated cardiomyopathy, longer duration of HF, and lower EF. One-year survival was 77% in QRS ≥120 vs. 82% in QRS <120 ms, and 5-year survival was 42 vs. 51%, respectively (P < 0.001). The adjusted hazard ratio for all-cause mortality was 1.11 (95% confidence interval 1.04-1.18, P = 0.001) for QRS ≥120 vs. <120 ms. There was no interaction between QRS width and EF.

CONCLUSION

QRS prolongation is associated with other markers of severity in HF but is also an independent risk factor for all-cause mortality. The risk associated with QRS prolongation may be similar regardless of EF. This provides a rationale for trials of CRT in HF with preserved EF.

Relationship between mechanical and electrical remodelling in patients with cardiac resynchronization implanted defibrillators

AIMS

Cardiac resynchronization therapy (CRT) is associated with reverse left ventricular (LV) remodelling. However, the effects of CRT-induced mechanical remodelling on electrical remodelling, and the occurrence of ventricular arrhythmias have not been clearly established. We studied the relationship between mechanical remodelling, electrical remodelling, and the occurrence of appropriate implantable cardioverter-defibrillator (ICD) therapy 1 year after CRT.

METHODS AND RESULTS

We analysed data from 45 patients who underwent ICD-CRT implantation at our centre. Significant LV reverse remodelling was defined by a minimum 10% decrease in the LV end-diastolic diameter (LVEDd) at 1 year of follow-up. Electrocardiographic indices of dispersion of repolarization [QTc, Tpeak-Tend (Tp-e) and their dispersion] were measured immediately and 1 year post-CRT implantation. The occurrence of appropriate ICD therapy was noted for each patient. Patients with (n= 21) and without (n= 24) significant LV reverse remodelling had similar baseline characteristics. At 1 year of follow-up, patients with mechanical reverse LV remodelling exhibited a significant decrease in QTc (505 ± 42 vs. 485 ± 52 ms, P < 0.05) and Tp-e (107 ± 26 vs. 92 ± 22 ms, P < 0.0001). However, patients without mechanical LV reverse remodelling exhibited a significant increase in QT dispersion (29 ± 43 vs. 98 ± 47 ms, P = 0.002) and Tp-e dispersion (22 ± 21 vs. 54 ± 36 ms, P = 0.0001). Finally patients with mechanical LV reverse remodelling experienced a lower rate of ICD therapy (P = 0.0025) after a mean follow-up of 19 months.

CONCLUSION

Reverse LV mechanical remodelling is associated with reversal of electrical remodelling and a lower rate of appropriate ICD therapy following CRT.

Cardiac resynchronization therapy guided by cardiovascular magnetic resonance

Cardiac resynchronization therapy (CRT) is an established treatment for patients with symptomatic heart failure, severely impaired left ventricular (LV) systolic dysfunction and a wide (> 120 ms) complex. As with any other treatment, the response to CRT is variable. The degree of pre-implant mechanical dyssynchrony, scar burden and scar localization to the vicinity of the LV pacing stimulus are known to influence response and outcome. In addition to its recognized role in the assessment of LV structure and function as well as myocardial scar, cardiovascular magnetic resonance (CMR) can be used to quantify global and regional LV dyssynchrony. This review focuses on the role of CMR in the assessment of patients undergoing CRT, with emphasis on risk stratification and LV lead deployment.

Effect of medical therapy on left ventricular ejection fraction in patients with systolic heart failure and narrow QRS duration with and without ischemic heart disease and left ventricular mechanical dyssynchrony

We studied 99 consecutive patients with class III-IV systolic heart failure with a left ventricular ejection fraction (LVEF) < or =35% and a QRS duration <120 milliseconds. Patients with cardiac resynchronization therapy were excluded. Echocardiography was performed in all patients before and after optimal standard heart failure therapy. The septal-to-posterior wall motion delay (SPWMD) > or =130 milliseconds on echocardiogram was defined as left ventricular mechanical dyssynchrony (LVMD). Sixty-nine of 99 patients (70%) had ischemic heart disease. During follow-up of 15.2 +/- 9.8 months, LVEF improvement > or =15% was greater patients in nonischemic group (50%, 15/30) than in ischemic group (9%, 6/69; P < 0.001). After adjustment for age, gender, and clinical and echocardiographic characteristics, ischemic heart disease and grade of coronary disease were persistently related to LVEF improvement > or =15% (P = 0.03 and 0.02, respectively). Twenty of 99 patients (20%) had SPWMD > or =130 milliseconds (LVMD group), and 79 of 99 patients (80%) had SPWMD <130 milliseconds (non-LVMD group). LVEF increased in both groups (P = 0.005) during follow-up, but the percentage of patients with LVEF improvement > or =15% in LVMD was greater compared with patients without LVMD (40% versus 16%, respectively, P = 0.03). In conclusion, the improvement of LVEF in patients with systolic heart failure and narrow QRS was greater in patients with nonischemic heart disease and LVMD compared with patients with ischemic heart disease and absence of LVMD during medical therapy without cardiac resynchronization therapy.

Short-term hemodynamic effects of cardiac resynchronization therapy in patients with heart failure, a narrow QRS duration, and no dyssynchrony

BACKGROUND

Cardiac resynchronization therapy produces both short-term hemodynamic and long-term symptomatic/mortality benefits in symptomatic heart failure patients with a QRS duration >120 ms. This is conventionally believed to be due principally to relief of dyssynchrony, although we recently showed that relief of external constraint to left ventricular filling may also play a role. In this study, we evaluated the short-term hemodynamic effects in symptomatic patients with a QRS duration <120 ms and no evidence of dyssynchrony on conventional criteria and assessed the effects on contractility and external constraint.

METHODS AND RESULTS

Thirty heart failure patients (New York Heart Association class III/IV) with a left ventricular ejection fraction < or =35% who were in sinus rhythm underwent pressure-volume studies at the time of pacemaker implantation. External constraint, left ventricular stroke work, dP/dtmax, and the slope of the preload recruitable stroke work relation were measured from the end-diastolic pressure-volume relation before and during delivery of biventricular and left ventricular pacing. The following changes were observed during delivery of cardiac resynchronization therapy: Cardiac output increased by 25+/-5% (P<0.05), absolute left ventricular stroke work increased by 26+/-5% (P<0.05), the slope of the preload recruitable stroke work relation increased by 51+/-15% (P<0.05), and dP/dtmax increased by 9+/-2% (P<0.05). External constraint was present in 15 patients and was completely abolished by both biventricular and left ventricular pacing (P<0.05).

CONCLUSIONS

Cardiac resynchronization therapy results in an improvement in short-term hemodynamic variables in patients with a QRS <120 ms related to both contractile improvement and relief of external constraint. These findings provide a potential physiological basis for cardiac resynchronization therapy in this patient population.

Cross-correlation delay to quantify myocardial dyssynchrony from phase contrast magnetic resonance (PCMR) velocity data

PURPOSE

To apply cross-correlation delay (XCD) analysis to myocardial phase contrast magnetic resonance (PCMR) tissue velocity data and to compare XCD to three established "time-to-peak" dyssynchrony parameters.

MATERIALS AND METHODS

Myocardial tissue velocity was acquired using PCMR in 10 healthy volunteers (negative controls) and 10 heart failure patients who met criteria for cardiac resynchronization therapy (positive controls). All dyssynchrony parameters were computed from PCMR velocity curves. Sensitivity, specificity, and receiver operator curve (ROC) analysis for separating positive and negative controls were computed for each dyssynchrony parameter.

RESULTS

XCD had higher sensitivity (90%) and specificity (100%) for discriminating between normal and patient groups than any of the time-to-peak dyssynchrony parameters. ROC analysis showed that XCD was the best parameter for separating the positive and negative control groups.

CONCLUSION

XCD is superior to time-to-peak dyssynchrony parameters for discriminating between subjects with and without dyssynchrony and may aid in the selection of patients for cardiac resynchronization therapy.

Validation of an echocardiographic multiparametric strategy to increase responders patients after cardiac resynchronization: a multicentre study

AIMS

We sought to develop and validate a multiparametric algorithm by applying previously validated criteria to predict cardiac resynchronization therapy (CRT) response in a multicentre study. Thirty per cent of patients treated by CRT fail to respond to the treatment. Although dyssynchrony by echocardiography has been used to improve the selection of patients, the complexity of myocardial contraction has generated a moderate improvement using any of several individual parameters.

METHODS AND RESULTS

Two hundred end-stage heart failure patients [NYHA 3-4 and left ventricular ejection fraction (LVEF)<35%] with QRS>120 ms were included. Echocardiography analysis focused on the following parameters: atrioventricular dyssynchrony, interventricular dyssynchrony, and intraventricular dyssynchrony that integrated radial (PSAX M-mode) and longitudinal [tissue Doppler imaging (TDI)] evaluations for spatial (wall to wall) and temporal (wall end-systole to mitral valve opening) dyssynchrony diagnosis. Following CRT implantation, patients were monitored for 6 months with functional and echo evaluations defining responders by a 15% reduction in end-systolic volume. Mean QRS duration and LVEF were 152 +/- 17 ms and 25 +/- 8%. There was a CRT response in 57% of patients, independent of QRS width. Mean prevalence of positive criteria was 34 +/- 8%. Feasibility and variability averages were 81 +/- 20% and 9 +/- 4%. In a single parametric approach, ranges of sensitivities and specificities were 18-65% and 45-84% with a mean of 41% and 66%. A multiparametric approach by focusing on criteria combination decreased the mean rate of false-positive results to 14 +/- 12%, 5 +/- 4%, 2 +/- 2%, and 1 +/- 2% from one to four parameters, respectively. More than three parameters were associated with a specificity above 90% and a positive predictive value above 65%. Reproducibility of this global strategy was 91%.

CONCLUSION

A multiparametric echocardiographic strategy based on the association of conventional criteria is a better indicator of CRT response than the existing single parametric approaches.

Effectiveness of cardiac resynchronisation therapy in patients with echocardiographic evidence of mechanical dyssynchrony

OBJECTIVE

Cardiac resynchronisation therapy has proven to be effective in refractory heart failure (HF) patients with QRS >120-130 ms. Therefore, the aim of our study was to verify the long-term effectiveness of cardiac resynchronisation therapy in HF patients with echocardiographic evidence of mechanical asynchrony regardless of QRS duration.

METHODS

One hundred and six patients with New York Heart Association class II-IV HF and echocardiographic documentation of interventricular and intraventricular asynchrony underwent biventricular stimulation. A clinical and functional evaluation was performed at baseline, 1, 3, 6 months, and every 6 months thereafter.

RESULTS

After a median follow-up of 16 months, a significant improvement was noted in ejection fraction, left ventricular diameters, mitral regurgitation jet area, interventricular and intraventricular echocardiographic indexes of asynchrony, and the 6-min walking distance (P < 0.001 for all). Death rates for all causes and for cardiac causes were 18.2 (95% confidence interval 12.8-25.9) and 13.5 (95% confidence interval 9.0-20.3) per 100 person-years, respectively. Patients in New York Heart Association class IV had an almost three-fold increase in risk of dying as compared to class II-III (hazard ratio 2.97, 95% confidence interval 1.30-6.79).

CONCLUSIONS

Interventricular and intraventricular asynchrony at echocardiography may be useful in identifying HF patients suitable for cardiac resynchronisation therapy, with results comparable to those obtained with QRS duration selection criteria.

Results of the SCART study: selection of candidates for cardiac resynchronisation therapy

OBJECTIVE

To prospectively determine whether prespecified electrocardiographic, echocardiographic and tissue Doppler imaging (TDI) selection criteria may predict a positive response to cardiac resynchronisation therapy (CRT).

METHODS

In this multicentre, prospective, non-randomised study, 96 heart failure patients with New York Heart Association class III-IV symptoms, an ejection fraction of < or =35%, and at least one marker of ventricular dyssynchrony according to prespecified electrocardiographic, echocardiographic or TDI criteria were enrolled. The primary endpoint was an improvement in the clinical composite score at 6 months.

RESULTS

At enrolment, 70 patients fulfilled the electrocardiographic criterion (QRS duration > or =150 ms), 77 patients showed echocardiographic signs of dyssynchrony, and 37 patients met the TDI dyssynchrony criteria. The overall responder rate was 78/96 (81%). In particular, the primary endpoint was reached in 68 patients who fulfilled the echocardiographic criteria as compared with 10 patients who did not (88 vs. 53%, P = 0.001). The patients who met the echocardiographic criteria showed a significant greater reduction in left ventricular end-systolic diameter (P = 0.029) and a higher improvement in quality of life (P = 0.017) than patients who did not. Neither electrocardiographic nor TDI criteria seemed to predict a positive response to CRT.

CONCLUSIONS

In our patient population, mechanical indexes of dyssynchrony as assessed by echocardiography appeared to identify CRT responders. Although TDI is useful for evaluating ventricular dyssynchrony after CRT, the prespecified TDI inclusion criteria adopted in this investigation did not increase the number of CRT responders.

Measurements of mechanical asynchrony in patients with heart failure: is the puzzle completed?

Numerous randomized clinical trials demonstrated the beneficial effects of cardiac resynchronization therapy (CRT) in the treatment of moderate to severe heart failure. Despite careful patient selection, there is still a percentage of non-responders, that is as high as 30-50%. Patients are selected mainly on electrocardiogram criteria. Recent studies have observed that the severity of mechanical systolic asynchrony is a much better predictor of a response after CRT. Echocardiography allows a non-invasive evaluation atrioventricular and inter- and intraventricular synchrony; furthermore, recent advances have provided direct evidence of wall motion resynchronization in patients receiving CRT. Nevertheless, although many authors tried to search for the best echocardiographic index to identify systolic asynchrony, and consequently responders to CRT before the procedure, this issue is still a matter of debate. Our aim was to make an updated review of the more recent studies on this topic.

Changes and predictive value of dispersion of repolarization parameters for appropriate therapy in patients with biventricular implantable cardioverter-defibrillators

BACKGROUND

The impact of cardiac resynchronization therapy (CRT) on dispersion of repolarization is controversial. The benefit of CRT on sudden cardiac death has been demonstrated only after 3 years follow-up.

OBJECTIVE

The purpose of this study was to explore the immediate effect of CRT on dispersion of repolarization and to define the value of dispersion of repolarization parameters as predictors of appropriate implantable cardioverter-defibrillator (ICD) therapy.

METHODS

Data from 100 patients who underwent CRT-ICD placement were analyzed retrospectively. Patients had symptoms of New York Heart Association functional class III or IV heart failure, left ventricular ejection fraction < or =35%, and QRS duration >130 ms or QRS < or =130 ms with left intraventricular dyssynchrony. ECG indices of dispersion of repolarization before and immediately after CRT implantation (QT dispersion, Tpeak-Tend [Tp-e], and Tp-e dispersion) were measured.

RESULTS

In patients who were upgraded to a biventricular system, Tp-e did not increase significantly after CRT. However, Tp-e increased significantly after CRT in patients with left bundle branch block or narrow QRS at baseline. After 12-month follow-up, 22 patients had received appropriate ICD therapy. ICD therapy and no ICD therapy groups had similar baseline characteristics, such as secondary prevention and ischemic cardiomyopathy. Postimplantation Tp-e was the only independent predictor of future ICD therapy (P = .02).

CONCLUSION

Immediately after CRT, Tp-e did not increase in patients who received a biventricular upgrade; however, Tp-e did increase in patients with preimplantation left bundle branch block or narrow QRS. Postimplantation Tp-e was the only independent predictor of appropriate ICD therapy.

Long-term survival in patients treated with cardiac resynchronization therapy: a 3-year follow-up study from the InSync/InSync ICD Italian Registry

BACKGROUND

Studies reporting the long-term survival of patients treated with cardiac resynchronization therapy (CRT) outside the realm of randomized controlled trials are still lacking. The aim of this study was to quantify the survival of patients treated with CRT in clinical practice and to investigate the long-term effects of CRT on clinical status and echocardiographic parameters.

METHODS

The study population consisted of 317 consecutive patients with implanted CRT devices from eight Italian University/Teaching Hospitals. The patients were enrolled in a national observational registry and had a minimum follow-up of 2 years. A visit was performed in surviving patients and mortality data were obtained by hospital file review or direct telephone contact.

RESULTS

During the study period, 83 (26%) patients died. The rate of all-cause mortality was significantly higher in ischemic than nonischemic patients (14% vs 8%, P = 0.002). Multivariate analysis showed that ischemic etiology (HR 1.72, CI 1.06-2.79; P = 0.028) and New York Heart Association (NYHA) class IV (HR 2.87, CI 1.24-6.64; P = 0.014) were the strongest predictors of all-cause mortality. The effects of CRT persisted at long-term follow-up (for at least 2 years) in terms of NYHA class improvement, increase of left ventricular ejection fraction, decrease of QRS duration (all P = 0.0001), and reduction of left ventricular end-diastolic and end-systolic diameters (P = 0.024 and P = 0.011, respectively).

CONCLUSIONS

During long-term (3 years) follow-up after CRT, total mortality rate was 10%/year. The outcome of ischemic patients was worse mainly due to a higher rate of death from progressive heart failure. Ischemic etiology along with NYHA class IV was identified as predictors of death. Benefits of CRT in terms of clinical function and echocardiographic parameters persisted at the time of long-term follow-up.

Pacing in adults with congenital heart disease

Adults with congenital heart disease constitute one of the fastest growing populations in cardiology. Pacing is an integral part of their therapy and may reduce their morbidity and mortality significantly. The current generation of pacemakers is more sophisticated and complex, and they are being utilized for indications other than conduction abnormalities, such as termination of tachycardia and improvement of heart failure. The complex anatomy and history of multiple previous surgeries in adults with congenital heart disease, however, pose many limitations and technical challenges related to the placement of a pacemaker. Unique and innovative approaches to endocardial lead placement and improved epicardial leads is making pacemaker implantation more feasible in these patients.

Cardiac resynchronisation therapy in heart failure: Current status

Cardiac resynchronization in heart failure already has a history of 12 years. However, the major advances have been the result of large multi center trials dating from 2001. In all these trials patients with a LVEF < or = 35% were included, and a QRS above 120 msec. Follow up was from 3-36 months. The majority of these trials showed a positive effect in reduction of composite and points of death or hospitalization for major cardiovascular events. Many of these trials also showed a diminution of left ventricular and systolic diameter or volume. Even in NYHA class II patients an improvement was seen. Some unanswered questions still remain as regards the agreement on electrical or electromechanical dyssynchrony criteria. There is a number of patients with "wide" QRS who do not improve and conversely a number of patients with a narrow QRS who witness improvement. The benefit in patients with atrial fibrillation also remains unanswered. Finally the value of this modality in patients with mild heart failure or asymptomatic left ventricular systolic dysfunction, NYHA class I-II remains to be determined in large on going trials. Another question is whether biventricular or left ventricular patient is preferable. Finally whether biventricular patient should be complemented by a defibrillator insertion is being currently studied. Cardiac resynchronization therapy along or in combination with an ICD improves symptoms, reduces major morbidity and mortality in patients with a left ventricular EF<35%, ventricular dilatation and a QRS > or = 120 msec in NYHA class III-IV. Further indications are currently being examined.

Significance of QRS complex duration in patients with heart failure

Prolongation of QRS (> or =120 ms) occurs in 14% to 47% of heart failure (HF) patients. Left bundle branch block is far more common than right bundle branch block. Left-sided intraventricular conduction delay is associated with more advanced myocardial disease, worse left ventricular (LV) function, poorer prognosis, and a higher all-cause mortality rate compared with narrow QRS complex. It also predisposes heart failure patients to an increased risk of ventricular tachyarrhythmias, but the incidence of cardiac or sudden death remains unclear because of limited observations. A progressive increase in QRS duration worsens the prognosis. No electrocardiographic measure is specific enough to provide subgroup risk categorization for excluding or selecting HF patients for prophylactic implantable cardioverter-defibrillator (ICD) therapy. In ICD patients with HF, a wide underlying QRS complex more than doubles the cardiac mortality compared with a narrow QRS complex. There is a high incidence of an elevated defibrillation threshold at the time of ICD implantation in patients with QRS > or =200 ms. Mechanical LV dyssynchrony potentially treatable by ventricular resynchronization occurs in about 70% of HF patients with left-sided intraventricular conduction delay, a fact that would explain the lack of therapeutic response in about 30% of patients subjected to ventricular resynchronization according to standard criteria relying on QRS duration. The duration of the basal QRS complex does not reliably predict the clinical response to ventricular resynchronization, and QRS narrowing after cardiac resynchronization therapy does not correlate with hemodynamic and clinical improvement. Mechanical LV dyssynchrony is best shown by evolving echocardiographic techniques (predominantly tissue Doppler imaging) currently in the process of standardization.

Clinical predictors of marked improvement in left ventricular performance after cardiac resynchronization therapy in patients with chronic heart failure

BACKGROUND

Previous studies have shown that cardiac resynchronization therapy (CRT) improves cardiac performance and decreases mortality and hospital admission rates. However, it is not yet clear which patients will benefit from the procedure the most. The purpose of the study was to identify the pre-implant characteristics that better predict which patients will have the best outcome after CRT.

METHODS

In this observational study, 156 patients were studied with echocardiography and a 6-minute walking test at baseline and 12 months after CRT.

RESULTS

After CRT, we observed an increase in left ventricular ejection fraction (+29.6%, P < .0001), a decrease in left ventricular end systolic volume (-26.4%, P < .0001), in the proportion of patients with grade 2-4 mitral regurgitation (from 47.1% to 34.0%, P = .002), and with NYHA functional class III-IV (from 83.2% to 11.6%, P < .0001), an increase in exercise tolerance (+31.1%, P < .0001). Sixty-two patients had a marked increase in left ventricular ejection fraction (> 10 units); the only independent predictor of a marked effect of CRT was the nonischemic etiology of heart failure. In patients with ischemic cardiomyopathy, the benefit on ejection fraction correlates inversely with the extension of the ischemic damage.

CONCLUSIONS

CRT improves left ventricular function and exercise tolerance in the long term. The nonischemic etiology of the cardiomyopathy is the only independent predictor of a marked effect of CRT; this is probably due to the absence of ischemic, nonviable scar tissue in these patients.

[Indication for cardiac resynchronization therapy: Consensus 2005]

The indication for cardiac resynchronization therapy (CRT) using biventricular pacing or ICD systems has to be highly differentiated to optimize the proportion of patients who derive significant symptomatic benefit from this therapy, on the one hand, and to avoid this invasive treatment in patients with a low probability of clinical success of CRT, on the other hand. As a consensus in 2005, it can be put forward that there is sufficient evidence for an indication for CRT from clinical studies for the following characteristics: 1) Heart failure in NYHA functional class III or IV (if cardiac recompensation to class III is at least temporarily successful), 2) left ventricular ejection fraction < or =35%, 3) QRS duration >130 ms, particularly if left bundle branch block is present, 4) sinus rhythm. In addition, available data also suggest an indication for CRT in patients with atrial fibrillation if the other criteria listed above are met. The indication for CRT is unclear in patients with other intraventricular conduction delay (particularly right bundle branch block) while patients with left bundle branch block and a QRS duration of 120-130 ms seem to benefit if echocardiographic criteria demonstrate ventricular dyssynchrony. Since a multiplicity of echocardiographic criteria of ventricular dyssynchrony exists which is neither standardized nor evaluated in large-scale randomized trials, ventricular dyssynchrony on echocardiography alone cannot be regarded as an established indication for CRT without a QRS complex > or =120 ms. Similarly, whether heart failure in functional state NYHA II should be regarded as a CRT indication is currently being investigated in the randomized RAFT and MADIT-CRT trials.

Cardiac resynchronization therapy and tools to identify responders

Heart failure is a major epidemic. Many people with heart failure struggle with refractory symptoms despite optimal medical therapy. Those with severe left ventricular dysfunction and ventricular conduction delay are at significant risk from either dying suddenly or dying from progression of their heart failure. Cardiac resynchronization therapy (CRT) improves hemodynamics and symptoms of heart failure and has recently been shown to improve survival. One problem facing the use of CRT is that 30% of patients fail to respond. The dominant theory is that QRS duration (electrical dyssynchrony) does not accurately reflect mechanical dyssynchrony. Echocardiographic tools have recently been developed that enable clinicians to assess the degree of mechanical dyssynchrony in patients being considered for CRT. These tools are able to predict with a significant amount of accuracy whether a patient will respond to CRT. This allows for a more refined approach to evaluating patients for CRT and optimizing the treatment of congestive heart failure.

Real-Time Three-Dimensional Echocardiography

Background— Left ventricular (LV) mechanical dyssynchrony (LVMD) has emerged as a therapeutic target using cardiac resynchronization therapy (CRT) in selected patients with chronic heart failure. Current methods used to evaluate LVMD are technically difficult and do not assess LVMD of the whole LV simultaneously. We developed and validated real-time 3D echocardiography (RT3DE) as a novel method to assess global LVMD.

Methods and Results— Eighty-nine healthy volunteers and 174 unselected patients referred for routine echocardiography underwent 2D echocardiography and RT3DE. RT3DE data sets provided time-volume analysis for global and segmental LV volumes. A systolic dyssynchrony index (SDI) was derived from the dispersion of time to minimum regional volume for all 16 LV segments. Healthy subjects and patients with normal LV systolic function had highly synchronized segmental function (SDI, 3.5±1.8% and 4.5±2.4%; P =0.7). SDI increased with worsening LV systolic function regardless of QRS duration (mild, 5.4±0.83%; moderate, 10.0±2%; severe LV dysfunction, 15.6±1%; P for trend <0.001). We found that 37% of patients with moderate to severe LV systolic dysfunction had significant dyssynchrony with normal QRS durations (SDI, 14.7±1.2%). Twenty-six patients underwent CRT. At long-term follow-up, responders demonstrated reverse remodeling after CRT with a significant reduction in SDI (16.9±1.1% to 6.9±1%; P <0.0001) and end-diastolic volume (196.6±17.3 to 132.1±13.5 mL; P <0.0001) associated with an increase in LV ejection fraction (17±2.2% to 31.6±2.9%; P <0.0001).

Conclusions— RT3DE can quantify global LVMD in patients with and without QRS prolongation. RT3DE represents a novel technique to identify chronic heart failure patients who may otherwise not be considered for CRT.

Heart failure hospitalization is more common in pacemaker patients with sinus node dysfunction and a prolonged paced QRS duration

OBJECTIVES

The purpose of this study was to determine whether a prolonged paced QRS duration increases the risk of cardiac dysfunction.

BACKGROUND

Right ventricular apical pacing mimics left bundle branch block, results in a prolonged QRS duration of variable duration, and causes ventricular desynchronization.

METHODS

In the Mode Selection Trial (MOST), QRS duration was measured in patients who had at least one paced ventricular complex recorded on 12-lead ECG within 3 months of enrollment (early) and after 9 months (late). Clinical endpoints including heart failure hospitalization, mortality, and atrial fibrillation were analyzed. A total of 1,026 patients were included in the analysis. Median age was 75 years (25th, 75th percentiles = 69, 80) and median ejection fraction prior to implant was 55% (45, 60). The cumulative percent ventricular pacing (DDDR and VVIR) was 81% over a median follow-up of 33 months. During period, 123 patients had heart failure hospitalization, 197 died, and 261 patients had atrial fibrillation.

RESULTS

Cox proportional hazards models demonstrated that paced QRS duration was a strong predictor of heart failure hospitalization (hazard ratio 1.15; 95% confidence interval 1.07,1.23) for each 10-ms increase in paced QRS duration (P = .001). The increased risk was unaffected by adjustment for other known predictors of heart failure hospitalization in the study. Paced QRS duration was not significant for mortality (P = .41) or atrial fibrillation (P = .20) when baseline QRS duration and other predictors were included.

CONCLUSIONS

Paced QRS duration is a significant, independent predictor of heart failure hospitalization in patients with sinus node dysfunction. A very long paced QRS duration is associated with increased heart failure hospitalization.

Selection and optimisation of biventricular pacing: the role of echocardiography

The quantification of ventricular dyssynchrony is a key factor in identifying patients with severe heart failure who may benefit from cardiac resynchronisation with biventricular pacing (BVP). Echocardiographic techniques appear to offer superior sensitivity and specificity than the ECG in selecting these patients. This paper reviews the scope of current echocardiographic techniques for guiding both patient selection and optimisation of device programming following implantation.

Advances in perioperative pacing

Cardiac resynchronization therapy with biventricular pacing has become a significant management tool in adults with heart failure. In children, right rather than just left ventricular failure, is a key problem in the postoperative period. Also, congenital heart defects vary widely in their nature and prognosis. There are now preliminary reports in the literature of the use of multiple temporary pacing sites after congenital heart surgery and acute comparison of the effects of unsynchronized versus synchronized pacing in the postoperative period. These studies support the use of cardiac resynchronization pacing at least as a temporary measure in cases of acute heart failure after surgery in patients with congenital heart disease.

QRS dispersion: an electrocardiographic index of systolic left ventricular dysfunction in patients with left bundle branch block

The presence of complete left bundle branch block (LBBB) in patients with congestive heart failure has been proposed to be a factor that negatively affects left ventricular (LV) systolic function. The aim of this study was to evaluate the relative predictive value of QRS dispersion (QRSD) and QRS duration (QRSd) in relation to systolic performance of the left ventricle. The ejection fraction of 130 consecutive patients with LBBB was evaluated by standard echocardiographic methods, whereas QRSd and QRSD were measured. It was demonstrated that QRSD in patients with complete LBBB is strongly related to LV contractility. We, therefore, suggest that this simple electrocardiographic index may serve as a useful screening test for detection of patients with LV systolic dysfunction.

Cardiac resynchronization therapy in congestive heart failure: Ready for prime time?

OBJECTIVES/BACKGROUND

The aim of this article is to critically review the data accumulated to date on the application of cardiac resynchronization therapy (CRT) via biventricular pacing techniques to manage patients with advanced heart failure. The data from studies evaluating the effects of long-term right ventricular (RV) pacing are also briefly reviewed.

METHODS

MEDLINE and selective journal searches of English-language reports and a search of references of relevant papers were conducted.

RESULTS

Cardiac dyssynchrony as reflected by a prolonged QRS complex, often in the form of left bundle branch block, is encountered in about 30% of patients with moderate-to-advanced heart failure. Among these patients, 10% to 15% are candidates for CRT via biventricular pacing. Accumulated evidence from randomized controlled studies over the last few years has indicated a significant hemodynamic and clinical improvement conferred by CRT to class III or IV heart failure patients with idiopathic or ischemic dilated cardiomyopathy having a low left ventricular ejection fraction (</=35%) and a wide QRS complex (>/=120-150 ms). Newer data suggest a significant reduction in overall mortality and heart failure hospitalization, particularly when CRT is combined with automatic defibrillator backup. Technical advances with percutaneous methods accessing the tributaries of the cardiac veins have raised the success rate of implantation of left ventricular leads to >90%. Further confirmation from ongoing trials is awaited, and more data from cost-effectiveness studies are needed before CRT is considered for prime time therapy in the heart failure population. If the data confirm a survival benefit from CRT, use of this electrical therapy at earlier stages of heart failure might be contemplated. New evidence from recent studies suggests a deleterious effect of the long-standing practice of producing an iatrogenic left bundle branch block by conventional RV apical pacing in patients receiving permanent pacemakers. Thus, having already become poignantly aware of the harmful effects of spontaneous left bundle branch block, this emerging new evidence about RV apical pacing would dictate a change of attitude and direct our attention to alternate sites of pacing, such as the left ventricle and/or the RV outflow tract, if not for all patients then at least for those with left ventricular dysfunction.

CONCLUSIONS

CRT offers hemodynamic and clinical improvement to patients with moderate-to-advanced heart failure, and it might significantly prolong survival in selected patients, particularly if devices with defibrillation backup are used. Further confirmatory data from randomized mortality trials are needed, and issues of cost efficacy must be resolved before this vital therapeutic alternative is ready for prime time therapy of heart failure patients.

[Evaluation of ventricular asynchronism by Doppler tissue imaging in patients with idiopathic dilated cardiomyopathy]

OBJECTIVES

To study ventricular asynchronism with tissue Doppler imaging in patients with primitive dilated cardiomyopathy and narrow QRS.

PATIENTS AND METHODS

We compared a group of patients with DCM and QRS < 120 ms (gr 1, n=25, 52+/-14 yrs, LVEF: 25+/-9%) with a group of normal patients (gr 2, n=16, 36+/-20 yrs). We measured the delays between the beginning of QRS and the beginnings of aortic (QA), mitral (QM), tricuspid (QT) and pulmonary (QP) flows, and of systolic (QSm) and protodiastolic (QEm) wall motion waves recorded with TDI in the basal portion of interventricular septum (IVS) and LV and RV free walls. We then calculated the differences QA-QP, QM-QT, the interparietal differences for QSm and QEm, and the maximal interparietal systolic (QSm max) and diastolic (QEm max) delays.

RESULTS

QA, QP, QM and QT were significantly lengthened in group 1 patients but there were no difference between both groups for QA-QP and QM-QT. There was a trend toward a lengthening of QSm and QEm in group 1 patients. Interparietal differences of QSm and QEm were similar in both groups; however, QSm max and QEm max were significantly longer in group 1 patients than in group 2.

CONCLUSION

Doppler study of patients with DCM and narrow QRS shows a lengthening of all electromechanical delays and suggests some degree of ventricular asynchronism by showing a significant increase in maximal interparietal systolic and diastolic delays.

Recent advances in pacemaker and implantable defibrillator therapy for young patients

PURPOSE OF REVIEW

This review is intended to highlight major clinical advances over the past year related to (1). biventricular pacing as a treatment for dilated myopathy, (2). growing clinical experience with implantable cardioverter defibrillators in pediatrics, (3). technical advances in standard antibradycardia pacing, and (4). an appraisal of the newly updated ACC/AHA/NASPE guidelines for device implant in children and adolescents.

RECENT FINDINGS

Complex rhythm devices are being used more frequently in children. Biventricular pacing to improve ventricular contractility is a rapidly evolving technology that has now been applied to children and young adults with intraventricular conduction delay, such as bundle branch block after cardiac surgery. Implantable defibrillators are also being used for an expanding list of conditions, although lead dysfunction is seen as a fairly common complication in active young patients. Guidelines for device implantation have been developed, but the weight of evidence remains somewhat limited by the paucity of pediatric data in this field.

SUMMARY

Thanks to refinements in lead design and generator technology, coupled with rapidly expanding clinical indications, pacemakers and implantable defibrillators have become increasingly important components of cardiac therapy for young patients. Expanded multicenter clinical studies will be needed to develop more objective guidelines for use of this advanced technology.