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

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.

Intra-left ventricular systolic asynchrony in patients with overt hyperthyroidism

Hyperthyroidism causes a variety of adverse effects on the cardiovascular system. Left ventricular (LV) asynchrony is defined as loss of the simultaneous peak contraction of corresponding cardiac segments. The aim of this study was to assess systolic asynchrony in patients with overt hyperthyroidism. Asynchrony was evaluated in 27 patients with overt hyperthyroidism and 21 controls. All the patients and controls were subjected to a tissue synchronization imaging (TSI). The time to regional peak systolic tissue velocity (Ts) in LV by the six-basal-six-mid-segmental model was measured on ejection phase TSI images and four TSI parameters of systolic asynchrony were computed. All TSI parameters of LV asynchrony increased in hyperthyroid patients compared to controls: the standard deviation (SD) of the 12 LV segments Ts (35.7±14.4 vs 20.1±10.1, P<0.0001); the maximal difference in Ts between any 2 of the 12 LV segments (111.9±40.7 vs 65.9±30.7, P<0.0001); the SD of the 6 basal LV segments (31.2±18.2 vs 16.8±9.7, P=0.01); and the maximal difference in Ts between any 2 of the 6 basal LV segments (76.6±42.0 vs 44.4±25.7, P=0.005). Patients with overt hyperthyroidism present evidence of LV asynchrony by TSI.

Relation of QRS shortening to cardiac output during temporary resynchronization therapy after cardiac surgery

Cardiac resynchronization therapy (CRT) can improve cardiac function in heart failure without increasing myocardial oxygen consumption. However, CRT optimization based on hemodynamics or echocardiography is difficult. QRS duration (QRSd) is a possible alternative optimization parameter. Accordingly, we assessed QRSd optimization of CRT during cardiac surgery. We hypothesized that QRSd shortening during changes in interventricular pacing delay (VVD) would increase cardiac output (CO). Seven patients undergoing coronary artery bypass, aortic or mitral valve surgery with left ventricular (LV) ejection fraction < or =40%, and QRSd > or =100 msec were studied. CRT was implemented at epicardial pacing sites in the left and right ventricle and right atrium during VVD variation after cardiopulmonary bypass. QRSd was correlated with CO from an electromagnetic aortic flow probe. Both positive and negative correlations were observed. Correlation coefficients ranged from 0.70 to -0.74 during VVD testing. Clear minima in QRSd were observed in four patients and were within 40 msec of maximum CO in two. We conclude that QRSd is not useful for routine optimization of VVD after cardiac surgery but may be useful in selected patients. Decreasing QRSd is associated with decreasing CO in some patients, suggesting that CRT can affect determinants of QRSd and ventricular function independently.

Can optimization of pacing settings compensate for a non-optimal left ventricular pacing site?

AIMS

Optimal left ventricular (LV) lead position improves the response to cardiac resynchronization therapy (CRT). However, in some patients it is not possible to position the LV lead at an optimal pacing site. The aim of this study was to determine whether optimization of the pacing settings atrioventricular delay (AVD) and interventricular delay (VVD) can compensate for a non-optimal LV pacing site.

METHODS AND RESULTS

In 16 patients with heart failure [New York Heart Association class III (13) or IV (3), median QRS duration of 172 ms and median LV ejection fraction of 20%] the acute haemodynamic effect of biventricular pacing was assessed at > or =2 pacing sites by the increase in maximum rate of LV pressure rise (%dP/dt(max)). At each site the AVD and VVD were optimized. Biventricular pacing with nominal settings at a non-optimal LV pacing site improved dP/dt(max) by 12.8% (-0.5 to 23.2%). This could be further improved by 6.5 percentage points (1.2-13.9) by optimization of pacing settings (P = 0.001) and by 9.9 percentage points (3.7-13.3, P = 0.004) by optimization of pacing site. Optimization of the LV pacing site and pacing settings together improved %dP/dt(max) by 16.2 per cent points (10.0-21.8, P < 0.001).

CONCLUSION

Optimization of the AVD and VVD can partly compensate for a non-optimal LV pacing site. However, a combination of an optimal LV pacing site and optimized pacing settings gives the best acute haemodynamic response.

Cardiac resynchronization therapy: assessment of dyssynchrony and effects on metabolism

In recent years cardiac resynchronization therapy has emerged as a promising new treatment strategy in a subgroup of patients with congestive heart failure and an asynchronous contraction pattern. By simultaneously pacing both right ventricular apex and lateral side of the left ventricle, ventricular synchrony can be partially restored and beneficial effects on cardiac performance can be observed. This review discusses the principles of ventricular dyssynchrony, and the acute and chronic effects of cardiac resynchronization therapy on systolic function, cardiac metabolism, and clinical parameters. Furthermore, the issue of identifying patients who do not respond to this therapy is addressed.

The utility of fragmented QRS complexes to predict significant intraventricular dyssynchrony in nonischemic dilated cardiomyopathy patients with a narrow QRS interval

BACKGROUND

Fragmented QRS complexes in the electrocardiograms (ECGs) of patients with coronary artery disease are associated with adverse cardiac events. However, there are limited data on its predictive usefulness in patients with nonischemic dilated cardiomyopathy. Left ventricular dyssynchrony is common in heart failure patients who have wide QRS intervals, but its frequency in patients with narrow QRS intervals is uncertain.

OBJECTIVES

To investigate the relationship between fragmented QRS complexes and intraventricular dyssynchrony in patients with nonischemic dilated cardiomyopathy in sinus rhythm.

METHODS

Sixty nonischemic dilated cardiomyopathy patients with sinus rhythm and narrow QRS intervals were recruited. Forty patients had a fragmented QRS in their basal ECG, and 20 patients did not have a fragmented QRS. Patients were analyzed for correlation between fragmented QRS complexes and intraventricular dyssynchrony.

RESULTS

The maximal difference in time to the peak myocardial systolic velocity between any two left ventricular segments (Max-ASE Sys), and maximal difference between Max-ASE Sys and the mean value of all segments (Max-ASE to Mean Sys) were significantly higher in patients with fragmented QRS complexes (P=0.001 and P=0.003, respectively). Seventy-two per cent of the patients with fragmented QRS complexes had significant left ventricular dyssynchrony; 15% of patients without fragmented QRS complexes had significant left ventricular dyssynchrony (P<0.0001). The presence of fragmented QRS complexes in leads corresponding to the specific ventricular segment in basal ECG was found to detect intraventricular dyssynchrony with 90.6% sensitivity (negative predictive value of 85%).

CONCLUSION

Fragmentation in the resting ECG is associated with significant intraventricular dyssynchrony in patients with nonischemic cardiomyopathy, narrow QRS and sinus rhythm. Fragmentation in ECG might be useful in identifying patients who could benefit from cardiac resynchronization therapy.

Usefulness and limitation of dobutamine stress echocardiography to predict acute response to cardiac resynchronization therapy

BACKGROUND

It has been hypothesized that a long-term response to cardiac resynchronization therapy (CRT) could correlate with myocardial viability in patients with left ventricular (LV) dysfunction. Contractile reserve and viability in the region of the pacing lead have not been investigated in regard to acute response after CRT.

METHODS

Fifty-one consecutive patients with advanced heart failure, LV ejection fraction <or= 35%, QRS duration > 120 ms, and intraventricular asynchronism >or= 50 ms were prospectively included. The week before CRT implantation, the presence of viability was evaluated using dobutamine stress echocardiography. Acute responders were defined as a >or=15% increase in LV stroke volume.

RESULTS

The average of viable segments was 5.8 +/- 1.9 in responders and 3.9 +/- 3 in nonresponders (P = 0.03). Viability in the region of the pacing lead had an excellent sensitivity (96%), but a low specificity (56%) to predict acute response to CRT. Mitral regurgitation (MR) was reduced in 21 patients (84%) with acute response. The presence of MR was a poor predictor of response (sensibility 93% and specificity 17%). However, combining the presence of MR and viability in the region of the pacing lead yields a sensibility (89%) and a specificity (70%) to predict acute response to CRT.

CONCLUSION

Myocardial viability is an important factor influencing acute hemodynamic response to CRT. In acute responders, significant MR reduction is frequent. The combined presence of MR and viability in the region of the pacing lead predicts acute response to CRT with the best accuracy.

Response to cardiac resynchronization therapy: is it time to expand the criteria?

BACKGROUND

Cardiac resynchronization therapy (CRT) is a promising treatment for a subgroup of patients with advanced congestive heart failure and a prolonged QRS interval. Despite the majority of patients benefiting from CRT, 10-40% of patients do not respond to this treatment and are labeled as nonresponders. Given that there is a lack of consensus on how to define response to CRT, the purpose of this viewpoint is to discuss currently used definitions and their shortcomings, and to provide recommendations as to how an expansion of the criteria for CRT response may be useful to clinicians.

METHODS AND RESULTS

Analysis of the literature and case reports indicates that the majority of established measures of CRT response, including New York Heart Association functional class and echocardiographic, hemodynamic, and neurohormonal parameters, are poor associates of patient-reported symptoms and quality of life. Moreover, the potential moderating role of psychological factors in determining health outcomes after CRT has largely been neglected.

CONCLUSIONS

It is recommended to routinely assess health status after CRT with a disease-specific questionnaire in standard clinical practice and to examine its determinants, including psychological factors such as personality traits and depression. This may lead to improved (secondary) treatment and prognosis in CHF patients treated with CRT.

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.

Cardiac magnetic resonance assessment of dyssynchrony and myocardial scar predicts function class improvement following cardiac resynchronization therapy

OBJECTIVES

We tested a circumferential mechanical dyssynchrony index (circumferential uniformity ratio estimate [CURE]; 0 to 1, 1 = synchrony) derived from magnetic resonance-myocardial tagging (MR-MT) for predicting clinical function class improvement following cardiac resynchronization therapy (CRT).

BACKGROUND

There remains a significant nonresponse rate to CRT. MR-MT provides high quality mechanical activation data throughout the heart, and delayed enhancement cardiac magnetic resonance (DE-CMR) offers precise characterization of myocardial scar.

METHODS

MR-MT was performed in 2 cohorts of heart failure patients with: 1) a CRT heart failure cohort (n = 20; left ventricular ejection fraction of 0.23 +/- 0.057) to evaluate the role of MR-MT and DE-CMR prior to CRT; and 2) a multimodality cohort (n = 27; ejection fraction of 0.20 +/- 0.066) to compare MR-MT and tissue Doppler imaging septal-lateral delay for assessment of mechanical dyssynchrony. MR-MT was also performed in 9 healthy control subjects.

RESULTS

MR-MT showed that control subjects had highly synchronous contraction (CURE 0.96 +/- 0.01), but tissue Doppler imaging indicated dyssynchrony in 44%. Using a cutoff of <0.75 for CURE based on receiver-operator characteristic analysis (area under the curve: 0.889), 56% of patients tested positive for mechanical dyssynchrony, and the MR-MT CURE predicted improved function class with 90% accuracy (positive and predictive values: 87%, 100%); adding DE-CMR (% total scar <15%) data improved accuracy further to 95% (positive and negative predictive values: 93%, 100%). The correlation between CURE and QRS duration was modest in all cardiomyopathy subjects (r = 0.58, p < 0.001). The multimodality cohort showed a 30% discordance rate between CURE and tissue Doppler imaging septal-lateral delay.

CONCLUSIONS

The MR-MT assessment of circumferential mechanical dyssynchrony predicts improvement in function class after CRT. The addition of scar imaging by DE-CMR further improves this predictive value.

Transmural variation in myosin heavy chain isoform expression modulates the timing of myocardial force generation in porcine left ventricle

Recent studies have shown that the sequence and timing of mechanical activation of myocardium vary across the ventricular wall. However, the contributions of variable expression of myofilament protein isoforms in mediating the timing of myocardial activation in ventricular systole are not well understood. To assess the functional consequences of transmural differences in myofilament protein expression, we studied the dynamic mechanical properties of multicellular skinned preparations isolated from the sub-endocardial and sub-epicardial regions of the porcine ventricular midwall. Compared to endocardial fibres, epicardial fibres exhibited significantly faster rates of stretch activation and force redevelopment (k(tr)), although the amount of force produced at a given [Ca2+] was not significantly different. Consistent with these results, SDS-PAGE analysis revealed significantly elevated expression of alpha myosin heavy chain (MHC) isoform in epicardial fibres (13 +/- 1%) versus endocardial fibres (3 +/- 1%). Linear regression analysis revealed that the apparent rates of delayed force development and force decay following stretch correlated with MHC isoform expression (r2 = 0.80 and r2 = 0.73, respectively, P < 0.05). No differences in the relative abundance or phosphorylation status of other myofilament proteins were detected. These data show that transmural differences in MHC isoform expression contribute to regional differences in dynamic mechanical function of porcine left ventricles, which in turn modulate the timing of force generation across the ventricular wall and work production during systole.

Assessment of left ventricular dyssynchrony by speckle tracking strain imaging comparison between longitudinal, circumferential, and radial strain in cardiac resynchronization therapy

OBJECTIVES

The objective of this study was to assess the usefulness of each type of strain for left ventricular (LV) dyssynchrony assessment and its predictive value for a positive response after cardiac resynchronization therapy (CRT). Furthermore, changes in extent of LV dyssynchrony for each type of strain were evaluated during follow-up.

BACKGROUND

Different echocardiographic techniques have been proposed for assessment of LV dyssynchrony. The novel 2-dimensional (2D) speckle tracking strain analysis technique can provide information on radial strain (RS), circumferential strain (CS), and longitudinal strain (LS).

METHODS

In 161 patients, 2D echocardiography was performed at baseline and after 6 months of CRT. Extent of LV dyssynchrony was calculated for each type of strain. Response to CRT was defined as a decrease in LV end-systolic volume >/=15% at follow-up.

RESULTS

At follow-up, 88 patients (55%) were classified as responders. Differences in baseline LV dyssynchrony between responders and nonresponders were noted only for RS (251 +/- 138 ms vs. 94 +/- 65 ms; p < 0.001), whereas no differences were noted for CS and LS. A cut-off value of radial dyssynchrony >/=130 ms was able to predict response to CRT with a sensitivity of 83% and a specificity of 80%. In addition, a significant decrease in extent of LV dyssynchrony measured with RS (from 251 +/- 138 ms to 98 +/- 92 ms; p < 0.001) was demonstrated only in responders.

CONCLUSIONS

Speckle tracking radial strain analysis constitutes the best method to identify potential responders to CRT. Reduction in LV dyssynchrony after CRT was only noted in responders.

Three-dimensional mapping of mechanical activation patterns, contractile dyssynchrony and dyscoordination by two-dimensional strain echocardiography: rationale and design of a novel software toolbox

Background

Dyssynchrony of myocardial deformation is usually described in terms of variability only (e.g. standard deviations SD's). A description in terms of the spatio-temporal distribution pattern (vector-analysis) of dyssynchrony or by indices estimating its impact by expressing dyscoordination of shortening in relation to the global ventricular shortening may be preferential. Strain echocardiography by speckle tracking is a new non-invasive, albeit 2-D imaging modality to study myocardial deformation.

Methods

A post-processing toolbox was designed to incorporate local, speckle tracking-derived deformation data into a 36 segment 3-D model of the left ventricle. Global left ventricular shortening, standard deviations and vectors of timing of shortening were calculated. The impact of dyssynchrony was estimated by comparing the end-systolic values with either early peak values only (early shortening reserve ESR) or with all peak values (virtual shortening reserve VSR), and by the internal strain fraction (ISF) expressing dyscoordination as the fraction of deformation lost internally due to simultaneous shortening and stretching. These dyssynchrony parameters were compared in 8 volunteers (NL), 8 patients with Wolff-Parkinson-White syndrome (WPW), and 7 patients before (LBBB) and after cardiac resynchronization therapy (CRT).

Results

Dyssynchrony indices merely based on variability failed to detect differences between WPW and NL and failed to demonstrate the effect of CRT. Only the 3-D vector of onset of shortening could distinguish WPW from NL, while at peak shortening and by VSR, ESR and ISF no differences were found. All tested dyssynchrony parameters yielded higher values in LBBB compared to both NL and WPW. CRT reduced the spatial divergence of shortening (both vector magnitude and direction), and improved global ventricular shortening along with reductions in ESR and dyscoordination of shortening expressed by ISF.

Conclusion

Incorporation of local 2-D echocardiographic deformation data into a 3-D model by dedicated software allows a comprehensive analysis of spatio-temporal distribution patterns of myocardial dyssynchrony, of the global left ventricular deformation and of newer indices that may better reflect myocardial dyscoordination and/or impaired ventricular contractile efficiency. The potential value of such an analysis is highlighted in two dyssynchronous pathologies that impose particular challenges to deformation imaging.

Mechanical dyssynchrony or myocardial shortening as MRI predictor of response to biventricular pacing?

PURPOSE

To investigate whether mechanical dyssynchrony (regional timing differences) or heterogeneity (regional strain differences) in myocardial function should be used to predict the response to cardiac resynchronization therapy (CRT).

MATERIALS AND METHODS

Baseline mechanical function was studied with MRI in 29 patients with chronic heart failure. Using myocardial tagging, two mechanical dyssynchrony parameters were defined: the standard deviation (SD) in onset time (T onset) and in time to first peak (T peak,first) of circumferential shortening. Electrical dyssynchrony was described by QRS width. Further, two heterogeneity parameters were defined: the coefficient of variation (CV) in end-systolic strain and the difference between peak septal and lateral strain (DiffSLpeakCS). The relative increase in maximum rate of left ventricle pressure rise (dP/dt max) quantified the acute response to CRT.

RESULTS

The heterogeneity parameters correlated better with acute response (CV: r = 0.58, DiffSLpeakCS: r = 0.63, P < 0.005) than the mechanical dyssynchrony parameters (SD(T onset): r = 0.36, SD(T peak,first) r = 0.47, P = 0.01, but similar to electrical dyssynchrony (r = 0.62, P < 0.001). When a heterogeneity parameter was combined with electrical dyssynchrony, the correlation increased (r > 0.70, P incr < 0.05).

CONCLUSION

Regional heterogeneity in myocardial shortening correlates better with response to CRT than mechanical dyssynchrony, but should be combined with electrical dyssynchrony to improve prediction of response beyond the prediction from electrical dyssynchrony only.

Quantitative comparison of 2D and 3D circumferential strain using MRI tagging in normal and LBBB hearts

The response to cardiac resynchronization therapy (CRT), which is applied to patients with heart failure (HF) and left bundle-branch block (LBBB), can be predicted from the mechanical dyssynchrony measured on circumferential strain. Circumferential strain can be assessed by either 2D or 3D strain analysis. In this study was evaluated the difference between 2D and 3D circumferential strain using MR tagging with high temporal resolution (14 ms). Six healthy volunteers and five patients with LBBB were evaluated. We compared the 2D and 3D circumferential strains by computing the mechanical dyssynchrony and the cross correlation (r) between 2D and 3D strain curves, and by quantifying the differences in peak circumferential shortening, time to onset, and time to peak of shortening. The obtained maximum r(2) values were 0.97 +/- 0.03 and 0.87 +/- 0.16 for the healthy and LBBB populations, respectively, and thus showed a good similarity between 2D and 3D strain curves. No significant difference was observed between 2D and 3D in time to onset, time to peak, or peak circumferential shortening. Thus, to measure dyssynchrony, 2D strain analysis will suffice. Since 2D analysis is easier to implement than 3D analysis, this finding brings the application of MRI tagging and strain analysis closer to the clinical routine.

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.

[Which patients with heart failure should be offered cardiac resynchronization?]

Chronic heart failure is a very prevalent disease in developed countries. In recent decades, very important advances in drug therapy have occurred. However, mortality is still very high. One third of patients with a low ejection fraction and New York Heart Association (NYHA) functional class IIII-IV have a wide QRS. This means that there is often resynchronization of contraction and higher mortality. In order to improve the prognosis, the therapy based on cardiac resynchronization device has bee4n shown to be a complementary medical treatment and has contributed to clinical, hemodynamic and mortality improvements. In this article, we aim to show the results of clinical trials and recommendations of the main guidelines regarding this therapy.

Effect of Posterolateral Left Ventricular Scar on Mortality and Morbidity following Cardiac Resynchronization Therapy

OBJECTIVES

To determine the effect of a posterolateral (PL) left ventricular scar on mortality and morbidity following cardiac resynchronization therapy (CRT).

METHODS

Sixty-two patients with heart failure (age 67.3 +/- 9.6 yrs [mean +/- SD], 45 males, New York Heart Association class [NYHA] class III or IV, left ventricular ejection fraction [LVEF]= 35%, left bundle branch block, QRS > or = 120 ms) underwent late gadolinium enhancement cardiovascular magnetic resonance (LGE-CMR) for scar imaging. Patients were followed up for 741 (75-1602) days (mean [range]).

RESULTS

The presence of a PL scar emerged as an independent predictor of the composite endpoint of cardiovascular death or hospitalization for worsening heart failure (HR: 3.06 [1.63, 7.7, P < 0.0001]) as well as the endpoint of cardiovascular death (HR: 2.63 [1.39, 6.65], P = 0.0016). A transmural PL scar was the strongest predictor of these endpoints (both P < 0.0001). The symptomatic responder rate (improvement by > or =1 NYHA classes or > or =25% in 6-min walking distance) was 83% in the group with non-PL scars, but only 47% in the group with transmural PL scars (P < 0.0001). Pacing over the scar was associated with a higher mortality and morbidity than pacing outside the scar (all P < 0.05).

CONCLUSIONS

A PL scar is associated with a worse clinical outcome following CRT, particularly if it is transmural. Pacing scarred left ventricular myocardium carries a greater risk of mortality and morbidity than pacing nonscarred myocardium.

Prognostic value of tissue Doppler-derived ventricular asynchrony in patients with left bundle branch block but not advanced heart failure

OBJECTIVES

The aim of the present study was to evaluate the prognostic significance of tissue Doppler echocardiography (TDE)-derived ventricular asynchrony in patients with left bundle branch block (LBBB) but not advanced heart failure.

METHODS

Fifty-five patients (mean age 66 +/- 13 years; 33 male) with complete LBBB (QRS > 120 ms) hospitalized for an acute episode of decompensated heart failure and in New York Heart Association class II for at least 6 months before the study admission underwent standard Doppler echo and pulsed-wave TDE. Precontraction time (PCTm) from the beginning of Q wave of electrocardiogram to the onset of systolic myocardial velocity wave was evaluated in four different left ventricular (LV) basal myocardial segments (LV anterior, inferior, septal and lateral walls) and in one right ventricular (RV) lateral wall. Intraventricular activation delay (IntraV-del) was calculated by the difference of PCTm of each LV myocardial segment. Interventricular activation delay (InterV-del) was calculated by the difference of PCTm between the most delayed LV segment and RV lateral wall.

RESULTS

The mean value of EF was 40 +/- 9% and of InterV-del, IntraV-del was, respectively (97.4 +/- 46.7 and 57.9 +/- 35.5 ms). InterV-del was inversely related to EF (r = -0.68; P < 0001). During the follow-up (26 months, range 11-37 months) cardiac events were recorded in 23 (41%) patients: a worsening of heart failure (WHF) in 23 patients and cardiac death in ten patients. Cox proportional hazard multivariate analysis showed that age, and InterV-del [HR = 1.02 (P < 0.05) and 1.03 (P < 0005)] predicted mortality. A Receiver operating characteristic analysis showed that a cut-off value of InterV-del 100 ms (AUC = 0.86; P < 0001) predicted WHF and mortality with sensitivity and specificity of 75% and 90%; 81% and 84%, respectively.

CONCLUSIONS

TDE-derived interventricular asynchrony represents a prognostic indicator of major cardiac events at 2 years of follow-up in patients with LBBB but not advanced heart failure.

New Insight Into Left Ventricular Reverse Remodeling After Biventricular Pacing Therapy for Heart Failure

Biventricular pacing has been consistently shown to improve symptoms and exercise capacity in patients with advanced heart failure and wide QRS complexes. Recent data have shown that biventricular pacing has the propensity to reduce left ventricular volume, a condition referred to as reverse remodeling. Since the authors initial description of successful left ventricular reverse remodeling after biventricular pacing therapy, data from multicenter trials have grown and consistently support the observation. In addition to the volumetric change, there was also progressive improvement of left ventricular systolic function and clinical status. The authors subsequent data also illustrated that the benefits on reverse remodeling and left ventricular systolic function were pacing dependent and disappeared gradually when pacing was withdrawn. With the use of tissue Doppler imaging, a substantial proportion of patients were found who had mechanical delay in the free wall. During biventricular pacing, all the segments were homogenously delayed resulting in a late, albeit synchronous, systolic contraction.

Imaging techniques in cardiac resynchronization therapy

Cardiac resynchronization therapy is a high cost therapeutic option with proven efficacy on improving symptoms of ventricular failure and for reducing both hospitalization and mortality. However, a significant number of patients do not respond to cardiac resynchronization therapy that is due to various reasons. Identification of the optimal pacing site is crucial to obtain the best therapeutic result that necessitates careful patient selection. Currently, using echocardiography for mechanical dyssynchrony assessment performs patient selection. Multi-Detector-Row Computed Tomography (MDCT) and Magnetic Resonance Imaging (MRI) are new imaging techniques that may assist the cardiologist in patient selection. These new imaging techniques have the potential to improve the success rate of cardiac resynchronization therapy, due to pre-interventional evaluation of the venous coronary anatomy, to evaluation of the presence of scar tissue, and to improved evaluation of mechanical dyssynchrony. In conclusion, clinical issues associated with heart failure in potential candidates for cardiac resynchronization therapy, and the information regarding this therapy that can be provided by the imaging techniques echocardiography, MDCT, and MRI, are reviewed.

Prevalence of Mechanical Dyssynchrony in Heart Failure Patients with Different QRS Durations

BACKGROUND

Cardiac resynchronization therapy (CRT) has emerged as an established therapy for congestive heart failure. However, up to 30% of patients fail to respond to CRT despite prolonged QRS.

OBJECTIVES

This study aimed at defining the prevalence of interventricular and intraventricular dyssynchrony in heart failure patients with different QRS durations.

METHODS

A total of 123 consecutive patients with severe heart failure (LVEF < 35% and NYHA class III-IV) were prospectively evaluated using 12-lead electrocardiogram and complete echocardiographic examination including tissue Doppler imaging.

RESULTS

According to the QRS duration, 56 patients had a QRS duration < or = 120 ms (Group 1), 33 patients had a QRS duration between 120 and 150 ms (Group 2), and 34 patients had a QRS duration > or = 150 ms (Group 3). Intraventricular dyssynchrony was present in 36% of Group 1 patients, in 58% of Group 2 patients, and in 79% of Group 3 patients (P < 0.000). Linear regression demonstrated a weak relation between QRS and intraventricular dyssynchrony. A greater proportion of patients with interventricular dyssynchrony was observed in Group 3 or Group 2 compared to patients with normal QRS duration (32% in Group 1 vs. 51.5% in Group 2 vs. 76.5% in Group 3, P < 0.000). Linear regression demonstrated a significant relation between QRS duration and interventricular mechanical delay.

CONCLUSIONS

Although both interventricular and intraventricular dyssynchrony increased with the increasing QRS duration, the correlation between intraventricular mechanical and electrical dyssynchrony was weak. The lack of intraventricular dyssynchrony in a fraction of patients with standard CRT indication by QRS duration may provide us insight into the nonresponders rates.

Prevalence of Dyssynchrony Derived from Echocardiographic Criteria in Heart Failure Patients with Normal or Prolonged QRS Duration

Cardiac resynchronization therapy (CRT) for heart failure is targeted at specific patients with mechanical dyssynchrony. We aimed to evaluate the prevalence of dyssynchrony in heart failure patients with either normal or prolonged QRS duration using Doppler imaging. Sixty heart failure patients with idiopathic dilated cardiomyopathy (30 with prolonged QRS duration 30 with normal QRS duration) underwent standard echocardiography and tissue Doppler imaging examinations. Difference between left and right ventricular pre-ejection intervals of more than 40 msec was considered a marker of interventricular dyssynchrony. Intraventricular dyssynchrony was defined as a delay of 60 msec between the time to peak velocities of the septum and left ventricular lateral wall. Patients who have either intra- or interventricular dyssynchrony were defined as with cardiac dyssynchrony. Dyssynchrony was observed in 7 (23.3%) heart failure patients with normal QRS duration versus 26 (86.7%) patients with prolonged QRS duration. There was significant difference between the prevalence of dyssynchrony derived from echo criteria in two groups (P<0.05). Although patients with prolonged QRS duration have a high prevalence of dyssynchrony, yet some still have good cardiac synchronicity. Moreover, dyssynchrony also exists in a small percentage of heart failure patients with normal QRS duration. To identify the potential responders for CRT, both QRS duration and cardiac synchronicity should be assessed.

Cardiac resynchronization therapy: from creation to evolution--an evidence-based review

In the past decade, cardiac resynchronization therapy (CRT), achieved by simultaneous left and right ventricular pacing, has emerged as a potent therapeutic option for patients with congestive heart failure. Electrical dyssynchrony, most often manifested by left bundle branch block on the surface 12-lead electrocardiogram, results in mechanical dyssynchrony of the left ventricular septum and free wall, which decreases cardiac efficiency. In patients with ejection fractions <30%, New York Heart Association (NYHA) class III or IV, and QRS width >120 ms, CRT improves clinical parameters such as 6-minute walk distances, quality-of-life scores, and NYHA functional class. Long-term reverse remodeling of the failing ventricle results in reductions in congestive heart failure hospitalizations and mortality independent of defibrillator therapy. While most patients show significant improvement, a small proportion fail to respond. Appropriately identifying patients who will benefit most from CRT and timing the initiation of resynchronization therapy remain areas of intense investigation.

Sustained Benefit of Cardiac Resynchronization Therapy

INTRODUCTION

Most data on cardiac resynchronization therapy (CRT) are from trials with highly selected patients, with limited long-term echocardiographic data. This study was performed to evaluate long-term echocardiographic remodeling after CRT in daily practice.

METHODS AND RESULTS

A biventricular pacemaker was implanted in 130 patients with advanced heart failure who met the general accepted criteria for CRT or in heart failure patients with a conventional pacemaker indication. Two years echocardiographic follow-up was available. Mean age (73 years) was higher than in the randomized trials. Forty-one patients (32%) died during the 2 year follow-up period. Mortality was higher in males, in patients with increased NT-proBNP, renal dysfunction, or left atrial dilatation before implantation. Echocardiographic response (LVEF improvement of 5% or more) was documented in 69, 88, and 91% of the survivors, after 3 months, 1 year, and 2 years, respectively. Echocardiographic response after 3 months was associated with a significantly higher long-term survival (P = 0.04). Mean LVEF was 22% at baseline compared to 31.8, 38.3, and 39.7% after 3 months, 1 year, and 2 years, respectively (P < 0.01). Reverse remodeling (a reduction of LV end systolic volume of more than 10%) was observed in 70.7, 81.0, and 91.7% of the survivors after 3 months, 1 year, and 2 years, respectively. Long-term LV improvement was more pronounced in patients with nonischemic cardiomyopathy.

CONCLUSION

LV reverse remodeling and beneficial echocardiographic changes were sustained during 2 years follow-up. A 5% or more increase in LVEF after 3 months was associated with a better long-term survival.

Cardiac resynchronization therapy in clinical practice: need for electrical, mechanical, clinical and logistic synchronization

Considering the relatively short history of cardiac resynchronization therapy (CRT), the amount of available evidence of efficacy is impressive, and effectiveness studies are now required. Transfer of our experimentally gained knowledge into the real world raises issues that call for synchronization among the many specialists involved in chronic heart failure (CHF) management and CRT decision making. From an economic perspective, the demonstrated ability of CRT to reduce hospitalizations could help ease the burden on health systems derived from the growing incidence of CHF. Recent American College of Cardiology/American Heart Association guideline revisions should encourage a synchronized approach to rational deployment of CRT in selected patients. Nevertheless, current QRS criteria for CRT candidacy do not directly address the key issue of identification of patients with a pacing-correctable mechanical dyssynchrony (and in clinical trials, 25-30% of implanted patients did not respond to CRT). Echocardiography could become an important adjunct (or even an alternative) to QRS duration for patient selection; routine implementation would require use of straightforward, reproducible measurements, possibly obtainable on standard equipment. Echocardiography could also help optimize site location, although this would not eliminate lead placement problems. A series of issues remain open for investigation, including the potential of CRT in patients with atrial fibrillation, impact of devices with defibrillation ability, effects of electrical/pharmacological tailoring, need for confirmation that efficacy of CRT extends into the long term and possible use of CRT in mild CHF. Interdisciplinary synchronization in the various phases of CRT (screening, proposing, implementing, optimizing and monitoring) should eventually help develop a coordinated system for patient referral.

A prospective comparison of AV delay programming methods for hemodynamic optimization during cardiac resynchronization therapy

INTRODUCTION

There are several methods for programming the optimal AV delay (AVD) during cardiac resynchronization therapy (CRT). These include Doppler echocardiographic measurements of mitral inflow or aortic outflow velocities, an arbitrarily fixed AVD, and calculations based on intracardiac electrogram (EGM) intervals. The present study was designed to compare the acute effects of AVD programming methods during CRT.

METHODS AND RESULTS

We studied 28 patients at CRT implant with invasive measurements of LV dP/dt to determine the effect of AVD during atrial sensed (AS) and atrial paced (AP) modes. The optimal AVD, defined as that resulting in the maximal LV dP/dt, was then compared with that predicted by several noninvasive methods. CRT increased LV dP/dt 11% +/- 11% during AS (heart rate: 73 +/- 14 bpm) and 17% +/- 12% during AP (heart rate: 86 +/- 12 bpm) (P < 0.001 vs AS). There was an excellent correlation between the EGM method and the maximum achievable LV dP/dt (AS: R2 = 0.99, P < 0.0001, AP: R2 = 0.96, P < 0.0001) and this method performed better than other techniques.

CONCLUSIONS

An electrogram-based optimization method accurately predicts the optimal AVD among patients over a wide range of QRS intervals during CRT in both AS and AP modes. This simple technique may obviate the need for echocardiography for AVD programming.

Cardiac Resynchronization Therapy: A New Therapy for Advanced Congestive Heart Failure

Despite medical therapy, many patients with advanced systolic dysfunction remain highly symptomatic. In these patients the presence of a left bundle branch block on electrocardiogram indicates significant dyssynchrony of ventricular contraction. Cardiac resynchronization, by means of biventricular pacing, results in important clinical benefits. Due to the risk for malignant ventricular arrhythmias, this technology is best combined with an implantable cardioverter defibrillator.

Three Years of Cardiac Resynchronization Therapy: Could Superior Benefits be Obtained in Patients with Heart Failure and Narrow QRS?

AIM OF THE STUDY

To examine the long-term effects of cardiac resynchronization therapy (CRT) in patients presenting with heart failure (HF) and QRS </= 120 ms.

METHODS

This was a prospective, longitudinal study of 376 patients [mean age = 65 years, mean left ventricular (LV) ejection fraction (EF) = 29%, mean QRS duration = 165 ms, mean distance covered during a 6-minute hall walk (6-MHW) = 325 m], who underwent successful implantation of CRT systems. The QRS duration at baseline was </= 120 ms in 45 patients (12%) who were not pre-selected by echocardiographic criteria of dyssynchrony, and > 120 ms in the remaining 331 patients. The baseline characteristics of the 2 groups were similar. We evaluated indices of cardiac function, percentage of responders, and survival rates over a mean 28-month follow-up.

RESULTS

Both groups experienced similar long-term increases in 6-MHW, and decreases in New York Heart Association functional class and LV end-systolic volume (all comparisons P < 0.0001 in both groups). Time interaction of changes in LVEF and percentage of responders were significantly different (P = 0.03 and P = 0.004, respectively), in favor of the narrow QRS group, where the changes were sustained and persisted at 2 and 3 years. The long-term death rate from HF was lower in the group with narrow than in the group with wide QRS complex (P = 0.04; log-rank test).

CONCLUSIONS

CRT confers considerable long-term clinical, functional, and survival benefits in patients presenting with HF and narrow QRS, not preselected by echocardiographic criteria of dyssynchrony. Caution is advised before denying CRT to these patients on the basis of QRS width only.

Changes in pulse pressure variability during cardiac resynchronization therapy in mechanically ventilated patients

INTRODUCTION

The respiratory variation in pulse pressure (PP) has been established as a dynamic variable of cardiac preload which indicates fluid responsiveness in mechanically ventilated patients. The impact of acute changes in cardiac performance on respiratory fluctuations in PP has not been evaluated until now. We used cardiac resynchronization therapy as a model to assess the acute effects of changes in left ventricular performance on respiratory PP variability without the need of pharmacological intervention.

METHODS

In 19 patients undergoing the implantation of a biventricular pacing/defibrillator device under general anesthesia, dynamic blood pressure regulation was assessed during right ventricular and biventricular pacing in the frequency domain (power spectral analysis) and in the time domain (PP variation: difference between the maximal and minimal PP values, normalized by the mean value).

RESULTS

PP increased slightly during biventricular pacing but without statistical significance (right ventricular pacing, 33 +/- 10 mm Hg; biventricular pacing, 35 +/- 11 mm Hg). Respiratory PP fluctuations increased significantly (logarithmically transformed PP variability -1.27 +/- 1.74 ln mm Hg2 versus -0.66 +/- 1.48 ln mm Hg2; p < 0.01); the geometric mean of respiratory PP variability increased 1.8-fold during cardiac resynchronization. PP variation, assessed in the time domain and expressed as a percentage, showed comparable changes, increasing from 5.3% (3.1%; 12.3%) during right ventricular pacing to 6.9% (4.7%; 16.4%) during biventricular pacing (median [25th percentile; 75th percentile]; p < 0.01).

CONCLUSION

Changes in cardiac performance have a significant impact on respiratory hemodynamic fluctuations in ventilated patients. This influence should be taken into consideration when interpreting PP variation.