Presence Of Left Ventricular Dyssynchrony Research Articles

Interactions between myocardial sympathetic denervation and left ventricular mechanical dyssynchrony: A CZT analysis

BackgroundA correlation between left ventricular (LV) dyssynchrony (LVD) and impaired myocardial sympathetic tone has been hypothesized. We sought to assess the interactions between regional LV sympathetic innervation, perfusion, and mechanical dyssynchrony. MethodsEighty-three patients underwent evaluation of LV perfusion and sympathetic innervation on 99mTc-tetrofosmin/123I-metaiodobenzylguanidine (123I-MIBG) imaging. The summed rest score and summed 123I-MIBG score (SS-MIBG) were computed. The extent of “innervation/perfusion” mismatch was defined as the number of denervated LV segments with relatively preserved perfusion. LVD was evaluated on phase analysis and the wall with latest mechanical activation identified. ResultsLVD was revealed in 36 (43%) patients. Patients with LVD had more abnormal values of SRS (21 ± 9 vs 10 ± 8, P < 0.001) and SS-MIBG (29 ± 9 vs 17 ± 11, P < 0.001) than those without LVD. The presence of LVD also clustered with a higher burden of “innervation/perfusion” mismatch (P = 0.019). On per-wall analysis, LV walls with delayed mechanical activation showed a higher burden of “innervation/perfusion” mismatch (2.3 ± 1.4 segments) than normally contracting walls (1.3 ± 1.2 segments; P < 0.001). On multivariate analysis, the extent of “innervation/perfusion” mismatch was the only predictor of delayed mechanical activation (P = 0.029). ConclusionsPatients with LVD show an elevated burden of “innervation/perfusion” mismatch that is concentrated at the level of the most dyssynchronous walls.

Phase analysis in patients with reversible perfusion defects and normal coronary arteries at angiography

A count-based new technique from gated myocardial perfusion single-photon emission tomography (gMPS) was developed to allow the phase analysis providing information about the left ventricular (LV) regional discordance in contractility which is a measure of LV dyssynchrony. Since the phase analysis provides data for evaluating the dyssynchronous LV contraction, it has an important role in diagnosis and management of patients with left ventricular dysfunction. The aim of the study was to assess the presence of left ventricular dyssynchrony in patients with reversible perfusion defects on gMPS scans and normal or near normal coronary arteries at angiography. 32 patients (19 men, 59 %) with reversible mild perfusion defects on gMPS and normal coronary angiogram were retrospectively enrolled in the study. The peak of the phase histogram, the standard deviation of the phase distribution (PSD), the width of the band (PHB), and the symmetry and peakedness of the phase histogram, which are the assessment parameters for the LV dyssynchrony, were calculated from gMPS scans of patients by means of the phase analysis. Although, five quantitative variables are derived from the phase analysis of gMPS, PSD and PHB are two quantitative indices to assess LV global mechanical dyssynchrony and measurements of PSD (men 24.96 ± 7.31, women 24.26 ± 10.07) and PHB (men 70.1 ± 13.99, women 71.0 ± 30.4) were significantly higher than the those reported in the literature (p < 0.001). No significant differences in gMPS phase analysis indices were found between both sexes except kurtosis. As a conclusion, this study provides the phase analysis to detect LV mechanical dyssynchrony as new evidence supporting the concept that an abnormal scintigraphy finding, rather than being false-positive, may be an early marker of vasomotion changes associated with occult atherosclerosis in patients with normal coronary angiography findings.

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Left ventricular dyssynchrony assessment by phase analysis from gated PET-FDG scans

BackgroundThe outcome of patients with severe ischaemic left ventricular (LV) dysfunction is determined by the extent of myocardial viability and the presence of LV dyssynchrony. We aimed at assessing both parameters from the same imaging method, i.e. gated positron emission tomography (PET) F18-fluorodeoxyglucose (FDG) scans. MethodsPhase analysis from Emory Cardiac Toolbox was applied on gated PET-FDG scans to assess histogram bandwidth and standard deviation (SD) as a measure of LV dyssynchrony in 30 heart failure patients (mean ejection fraction: 30.2% ± 13.8%) referred for the evaluation of myocardial viability. Cut-off values from single-photon emission computed tomography myocardial perfusion imaging (SPECT-MPI) best predicting cardiac resynchronization therapy (CRT) response served as standard of reference (bandwidth < 135°; phase SD < 43°). Severe LV dyssynchrony was diagnosed if both SPECT-MPI values were above these limits. Intraclass correlation and clinical agreement in detection of severe LV dyssynchrony by PET vs SPECT were assessed. ResultsThere was a significant correlation between PET-FDG and SPECT-MPI for bandwidth (r = 0.88, P < .001) and phase SD (r = 0.88, P < .001) resulting in an excellent clinical agreement between the two methods of 93%. ConclusionsAccurate LV dyssynchrony assessment by phase analysis of gated PET-FDG scans is feasible, allowing assessing myocardial viability and severe LV dyssynchrony in one scan.

Prevalence of Dyssynchrony and Relation With Long-Term Outcome in Patients After Acute Myocardial Infarction

The impact of left ventricular (LV) dyssynchrony on the long-term outcomes of patients with acute myocardial infarction (AMI) remains unknown. The purpose of the present study was to evaluate the prevalence of LV dyssynchrony after AMI and the potential relation with adverse events. A total of 976 consecutive patients admitted with AMI treated with primary percutaneous coronary intervention were evaluated. Two-dimensional echocardiography was performed <48 hours after admission. LV dyssynchrony was assessed with speckle-tracking imaging and calculated as the time difference between the earliest and latest activated segments. Patients were followed up for the occurrence of all-cause mortality (the primary end point) or the composite secondary end point (heart failure hospitalization and all-cause mortality). Within 48 hours of admission for the index infarction, mean LV dyssynchrony was 61 ± 79 ms, and 14% of the patients demonstrated a ≥130-ms time difference, defined as significant LV dyssynchrony. During a mean follow-up period of 40 ± 17 months, 82 patients (8%) reached the primary end point. In addition, 36 patients (4%) were hospitalized for heart failure. The presence of LV dyssynchrony was associated with an increased risk for all-cause mortality and hospitalization for heart failure during long-term follow-up (adjusted hazard ratio 1.06, 95% confidence interval 1.05 to 1.08, p <0.001, per 10-ms increase). Moreover, LV dyssynchrony provided incremental value over known clinical and echocardiographic risk factors for the prediction of adverse outcomes. In conclusion, LV dyssynchrony is a strong predictor of long-term mortality and hospitalization for heart failure in a population of patients admitted with ST-segment elevation AMI treated with primary percutaneous coronary intervention.

Site of latest activation in patients eligible for cardiac resynchronization therapy: Patterns of dyssynchrony among different QRS configurations and impact of heart failure etiology

Cardiac resynchronization therapy (CRT) has emerged as a treatment option for patients with end-stage heart failure and a QRS duration ≥120 ms. Nonetheless, many patients with a prolonged QRS do not demonstrate left ventricular (LV) mechanical dyssynchrony, and discrepancies between electrical and mechanical dyssynchrony have been observed. In addition, several studies demonstrated that superior benefits after CRT could be achieved when the LV pacing lead was positioned at the most delayed myocardial segment. A total of 248 heart failure patients scheduled for CRT were included. In all patients, a 12-lead electrocardiogram and 2-dimensional echocardiogram were obtained. Patients were divided into 5 QRS configuration subgroups: narrow, left bundle-branch block, right bundle-branch block, intraventricular conduction delay, and right ventricular pacing. With speckle-tracking radial strain analysis, we evaluated time to peak radial strain. Next, the segments with the least and with the most mechanical activation delay were identified, and LV dyssynchrony was defined as the time delay between the two. Mean QRS duration was 164 ± 31 ms. Mean LV dyssynchrony in all patients was 186 ± 122 ms. Site of latest activation was predominantly located in the lateral (27%), posterior (26%), and inferior (20%) segments. Furthermore, extent of LV dyssynchrony was comparable between QRS configuration subgroups. An unequal distribution of LV segments with the most mechanical delay was observed in the left bundle-branch block and right ventricular pacing subgroups (P < .001 for both), whereas in the narrow, right bundle-branch block, and intraventricular conduction delay subgroups, a more homogeneous distribution was noted. No differences in distribution pattern or in extent of LV dyssynchrony were observed between ischemic and nonischemic heart failure patients. The lateral, posterior, and inferior segments take up 73% of the total latest activated segments in heart failure patients eligible for CRT. Presence of LV dyssynchrony can be observed in all QRS configurations. The site of latest activation may be outside the lateral or posterior segment, making echocardiographic assessment of LV dyssynchrony and site of latest activation a valuable technique to optimize patient outcome after CRT.

Cardiac resynchronization therapy: the issue of non-response

Cardiac resynchronization therapy reduces mortality and morbidity in heart failure patients with wide QRS and severe impairment of left ventricular systolic function, who are symptomatic despite optimal medical therapy. However, a high percentage of patients fail to show clinical or echocardiographic response to this treatment. Beyond current selection criteria, other elements, such as QRS duration and morphology, concomitant medical therapy, degree of right ventricle dysfunction, myocardial viability, presence of left ventricular dyssynchrony, and associated renal dysfunction, play a crucial role in modulating the response to cardiac resynchronization. Consequently, they should be part of the standard pre-implant evaluation, as they could be used to identify patients who are very unlikely to be responders.

Impact of Loading Condition on the 2D Speckle Tracking–Derived Left Ventricular Dyssynchrony Index in Nonischemic Dilated Cardiomyopathy

The effects of left ventricular (LV) loading conditions on LV dyssynchrony have not been elucidated. We modified LV loading conditions to reveal their effects on echocardiography-derived LV dyssynchrony index (LVdys) in patients with documented nonischemic dilated cardiomyopathy. Thirty-seven patients were consecutively enrolled. After baseline measurements, pneumatic compression of the lower extremities (Pcom) was used to increase LV afterload. Subsequently, sublingual nitroglycerin (SL-NG) was administered to modify preload. Conventional echocardiographic parameters, LVdys (by speckle-tracking radial strain analysis) and LV end-systolic wall stress (LV-ESWS), were calculated under each condition. LVdys-6 (defined as the maximal difference in time-to-peak radial strain between 6 myocardial segments) and LV-ESWS increased under Pcom (for LVdys-6, 159+/-117 at baseline versus 239+/-140 ms under Pcom, P<0.05; for LV-ESWS, 191+/-63 versus 228+/-80 g/m(2), P<0.05) After SL-NG application, both parameters decreased significantly (for LVdys-6, 239+/-140 under Pcom versus 147+/-103 ms after SL-NG, P<0.05; for LV-ESWS, 228+/-80 under Pcom versus 189+/-67 g/m(2) after SL-NG, P<0.05). When the presence of LV dyssynchrony was defined as the absolute difference in time-to-peak radial strain between the anteroseptal and posterior segments (LVdys-2), the results were unchanged. Using 130 ms as a cutoff value, the proportion of patients with LV dyssynchrony changed significantly (29.7% at baseline, 45.9% under Pcom, and 35.1% after SL-NG). When the presence of LV dyssynchrony was defined as standard deviation of the time to peak radial strain for 6 segments (LVdys-SD), the results were same. LVdys and LV-ESWS showed a modest but significant association with each other (r=0.47, P<0.001 for LVdys-6; r=0.41, P<0.001 for LVdys-2; r=0.46, P<0.001 for LVdys-SD). To the best of our knowledge, the present study provides the first evidence of a significant association between LVdys and LV loading status, reflective of a dynamic nature of LVdys. Accordingly, LV loading conditions should be taken into account when echocardiographic LVdys is used for clinical decision-making of selecting candidates for cardiac resynchronization therapy or when it is used as a surrogate marker of prognosis.

Left Ventricular Mechanical Dyssynchrony as Assessed by Phase Analysis of ECG‐Gated SPECT Myocardial Perfusion Imaging

Cardiac resynchronization therapy (CRT) has shown benefits in patients with severe heart failure. The traditional criteria to select patients for CRT (NYHA class III or IV, depressed left ventricular (LV) ejection fraction, and prolonged QRS duration) result in at least 30% of the selected patients with no response to CRT. Recent studies with tissue Doppler imaging (TDI) have shown that the presence of LV dyssynchrony is an important predictor for response to CRT. Phase analysis has been developed to assess LV dyssynchrony from electrocardiography-gated single photon emission computed tomography (GSPECT) myocardial perfusion imaging (MPI). This technique uses Fourier harmonic functions to approximate regional wall thickening over the cardiac cycle and to calculate phases of regional onset of mechanical contraction (OMC). These OMC phases are obtained three-dimensionally over the left ventricle to generate an OMC phase distribution. Quantitative indices are calculated from the phase distribution to assess degree of LV dyssynchrony. This technique has been compared to other methods of measuring LV dyssynchrony and shown promising results in clinical evaluations. In this review, the phase analysis methodology is described and its up-to-date validations are summarized.

A single session of haemodialysis improves left ventricular synchronicity in patients with end-stage renal disease: a pilot tissue synchronization imaging study

Mechanical left ventricular (LV) dyssynchrony impairs cardiac function in patients with heart failure and LV hypertrophy (LVH) and may be a factor contributing to the high incidence of cardiac deaths in patients with end-stage renal disease (ESRD). Objectives. To evaluate the possible presence of LV dyssynchrony in ESRD patients, and acute effect of haemodialysis (HD) on LV synchronicity using a tailored echocardiographic modality, tissue synchronization imaging (TSI). In 13 clinically stable ESRD patients (7 men; 65 +/- 10 years) with LVH, echocardiography data were acquired before and after a single HD session for subsequent off-line TSI analysis enabling the retrieval of regional intraventricular systolic delay data. Six basal and six midventricular LV segments were evaluated. Dyssynchrony was defined as a regional difference in time to peak systolic velocity >105 ms. Before HD, all patients had at least one dyssynchronous LV segment. The percentage of delayed segments correlated positively to LV end-diastolic diameter (r = 0.68, P < 0.05). HD induced a substantial decrease in the percentage of delayed segments from 36 +/- 25% to 19 +/- 14% (P < 0.01), reduced average maximal mechanical systolic LV delay from 300 +/- 89 to 225 +/- 116 ms (P < 0.05) and completely normalized LV synchronicity in three patients (23%). LV dyssynchrony appears to be present frequently in ESRD patients with LVH. The severity of LV dyssynchrony correlates with LV end-diastolic diameter and decreases after a single session of HD suggesting a mechanistic relevance of volume overload and possibly other toxins accumulating in HD patients.

Abstract 1647: Can Left Ventricular Dyssynchrony as evaluated by Phase Analysis on Gated Myocardial Perfusion SPECT predict Response to Cardiac Resynchronization Therapy?

Purpose: Cardiac resynchronization therapy (CRT) is now a well established therapeutic option for patients with end-stage heart failure. However, not all patients respond to CRT, and therefore preimplantation identification of responders is desirable. The purpose of the present study was to investigate whether the degree of left ventricular (LV) dyssynchrony as assessed with phase analysis from gated myocardial perfusion single photon emission computed tomography (GMPS), can predict which patients will respond to CRT. Methods: Forty-two patients with severe heart failure, depressed LV ejection fraction and wide QRS complex, were prospectively included for implantation of a CRT device and underwent GMPS and 2D echocardiography as part of clinical protocol. Clinical status was evaluated using New York Heart Association (NYHA) classification, 6-minute walk test and quality-of-life score. The histogram bandwidth and phase standard deviation (SD) (parameters indicating LV dyssynchrony) were assessed from GMPS, and clinical status and echocardiographic variables were re-assessed at 6 months follow-up. Results: Responders (71%) and non-responders (29%) had comparable baseline characteristics, except for histogram bandwidth (175±63° vs 117±51°, P &lt;0.01) and phase SD (56.3±19.9° vs 37.1±14.4°, P &lt;0.01) which were significantly larger in responders as compared to non-responders. Moreover, receiver-operator characteristic curve analysis demonstrated an optimal cutoff value of 135° for histogram bandwidth (sensitivity and specificity of 70%) and of 43° for phase SD (sensitivity and specificity of 74%) for the prediction of response to CRT. Conclusion: Response to CRT is related to the presence of LV dyssynchrony assessed by phase analysis with GMPS. A cutoff value of 135° for histogram bandwidth and of 43° for phase SD could be used to predict response to CRT. Larger prospective studies are warranted to confirm the present findings.

Frequency of inter- and intraventricular dyssynchrony in patients with heart failure according to QRS width

Cardiac resynchronization therapy (CRT) is an effective treatment for heart failure patients with prolongation of QRS duration. Despite careful patient selection, some do not respond to CRT based on QRS complex duration. We sought to evaluate the presence of left ventricular dyssynchrony using tissue Doppler imaging (TDI) according to QRS duration in heart failure patients. Ninety-nine patients (mean age 52.6 +/- 15.3 years) with severe heart failure [left ventricular (LV) ejection fraction, <35%] were prospectively evaluated. On the basis of QRS width, the patients were divided into two groups. Forty-eight patients (48.5%) had a normal QRS duration (<120 ms), Group I, and 51 (51.5%) had a prolonged QRS duration, Group II. All patients underwent echocardiography coupled with TDI. Spectral displays of six basal and six middle LV segments with pulsed-wave TDI were obtained to assess the time to peak systolic point from R-wave on electrocardiogram (Ts). The standard deviation of Ts (Ts-SD) and the maximal temporal difference of Ts (Ts-diff) were measured. Interventricular dyssynchrony [defined as the presence of an interventricular mechanical delay (IVMD) >40 ms] and intra-LV mechanical delays (defined as Ts-SD >33.4 ms and Ts-diff >100 ms) were correlated with the QRS width and morphology. We found a greater IVMD in Group II patients, compared with patients in Group I (42.5 +/- 22.3 vs. 26.8 +/- 21, respectively, P < 0.001). Intraventricular dyssynchrony defined as Ts-SD > or =33.4 ms was found in 45.1% of patients in Group II compared with 23% of patients in Group I (P = 0.03). Similarly, the Ts-diff was prolonged in Group II patients compared with Group I (P = 0.02). By linear regression analysis, a weak relation was found between Ts-SD and QRS duration (P = 0.055). A substantial portion of patients with prolonged QRS did not exhibit ventricular dyssynchrony defined either as total asynchrony index > or =33.4 ms or as IVMD >40 ms. A substantial proportion of patients with prolonged QRS (32.1%) did not exhibit inter- or intraventricular dyssynchrony, which may represent a limitation in identifying the ideal QRS interval for the selection of patients for CRT.

Severe Left Ventricular Dyssynchrony Is Associated With Poor Prognosis in Patients With Moderate Systolic Heart Failure Undergoing Coronary Artery Bypass Grafting

The objective of the present study was to assess the relationship between the presence of left ventricular (LV) dyssynchrony and clinical outcome in patients with moderate systolic heart failure undergoing coronary artery bypass graft (CABG) surgery. The presence of LV dyssynchrony is associated with poor prognosis in patients with LV dysfunction. The study consisted of 215 consecutive patients with ischemic cardiomyopathy and dyspnea (age 65 +/- 9 years, 81% male) undergoing CABG. Dyssynchrony was calculated by tissue Doppler imaging from regional time intervals in basal LV segments before and 1 month after CABG. Myocardial viability was assessed using single-photon emission computed tomography (SPECT) before CABG. Twenty-five patients (11.6%) died within 30 days (in-hospital mortality) of CABG. The presence of pre-CABG dyssynchrony > or =119 ms had the highest predictive accuracy for in-hospital mortality, with a sensitivity of 84% and a specificity of 71%. During the median follow-up period of 359 days (interquartile range 219 to 561), an additional 19 patients (10.3%) died and 34 patients (18.5%) were hospitalized for worsening heart failure. At Cox regression analysis, post-CABG dyssynchrony > or =72 ms and > or =5 viable segments were identified as independent predictors of clinical events, with a hazard ratio (HR) of 5.02, 95% confidence interval (CI) 2.57 to 10.02 (p < 0.001), and an HR of 0.63, 95% CI 0.55 to 0.75 (p < 0.001), respectively. Patients without post-CABG dyssynchrony and with viable myocardium had excellent prognosis compared with patients with severe post-CABG dyssynchrony and nonviable myocardium (event rate 3% vs. 64%; p < 0.001). The presence of severe LV dyssynchrony is associated with poor clinical outcomes despite revascularization. These results advocate a routine assessment of both LV dyssynchrony and viability to predict outcome in systolic heart failure patients undergoing CABG surgery.

Effect of Primary Mitral Regurgitation on Left Ventricular Synchrony

Mitral regurgitation (MR) promotes left ventricular (LV) dilatation and eccentric remodeling. In the presence of LV dyssynchrony and heart failure, cardiac resynchronization therapy decreases the severity of MR. Whether primary MR can cause LV dyssynchrony is unknown. We investigated whether moderate to severe primary MR causes LV dyssynchrony in the presence of LV dilation and an ejection fraction (EF) >55%. We studied 37 normal subjects and 22 patients with moderate to severe MR and no coronary artery disease. Electrocardiographically gated cine and tagged cardiac magnetic resonance imaging was performed. Two-dimensional, maximum-circumferential shortening strain and time-to-peak strain (TTPS) were computed using harmonic-phase analysis of tagged magnetic resonance imaging. LV dyssynchrony was assessed by comparing TTPS delay of various LV quadrants and TTPS dispersion among the contralateral quadrants in patients with MR and normal subjects. Statistical comparison was done using a generalized linear model for repeated measurements. LV end-diastolic and LV end-systolic volumes were significantly larger in patients with MR versus normal subjects (207 +/- 11 vs 130 +/- 4 and 73 +/- 5 vs 47 +/- 2 ml, p <0.001). LVEF did not differ in patients with MR and normal subjects. The difference in the TTPS among various quadrants and the dispersion among the contralateral quadrants of the LV myocardium was similar between patients with MR and normal subjects. In conclusion, moderate to severe MR does not cause LV dyssynchrony in patients with LV dilatation and normal LVEF. Thus, cardiac resynchronization therapy in the absence of LV dyssynchrony may not decrease the severity of MR.

Tissue Doppler Imaging of Mitral Annular Motion Is an Effective Surrogate of Left Ventricular Dyssynchrony and Predicts Response to Cardiac Resynchronization Therapy

Tissue Doppler imaging of basal myocardial segments has been used to predict response to cardiac resynchronization therapy (CRT). However, in patients with poor imaging windows mechanical dyssynchrony may be difficult to assess because of poor tissue characterization. We tested the hypothesis that tissue Doppler evaluation of the mitral annulus can accurately identify the presence of left ventricular dyssynchrony and predict the response to CRT. Tissue Doppler imaging of 6 mitral annular sites and 6 basal myocardial segments was performed in 21 patients with heart failure, before and at 3 months after CRT device implantation. Time to peak systolic velocity (T(s)) was determined for each site and intraventricular dyssynchrony was defined as the maximal difference in T(s) between measurement sites. Excellent correlation was observed between mitral annular and basal segment measurements of T(s) (r = 0.90, P < .001 at baseline and r = 0.93, P < .001 at follow-up) and maximal difference in T(s) between measurement sites (r = 0.90, P < .001 at baseline and r = 0.90, P = .003 at follow-up). Receiver operator characteristic analysis for the mitral annulus measurements demonstrated that an optimal cut-off value of T(s) = 179 milliseconds differentiated responders from nonresponders with a sensitivity of 86% and specificity of 82%; similarly, a cut-off value of maximal difference in T(s) between measurement sites = 105 milliseconds for intraventricular dyssynchrony differentiated responders from nonresponders with a sensitivity of 86% and specificity of 73%. Tissue Doppler assessment of mitral annular motion can accurately identify left ventricular dyssynchrony and predict positive response to CRT.

Postero‐Lateral Scar Tissue Resulting in Non‐Response to Cardiac Resynchronization Therapy

In large cardiac resynchronization therapy (CRT) trials, approximately 20-30% of patients did not respond to CRT. Recent studies indicated that left ventricular (LV) dyssynchrony is needed for response to CRT. However, the presence of LV dyssynchrony may not be the only determinant of response, because some patients with LV dyssynchrony do not benefit from CRT. In the current case report, we present a patient with ischemic cardiomyopathy, NYHA class III heart failure symptoms, and substantial LV dyssynchrony on tissue Doppler imaging who underwent CRT implantation but did not respond. Following CRT, LV dyssynchrony was not reduced and the patient did not improve in clinical symptoms or LV function. The lack of LV resynchronization was explained by the presence of extensive scar tissue in the region of the tip of the LV pacing lead resulting in ineffective LV pacing. In patients with ischemic cardiomyopathy and history of previous infarction, assessment of scar tissue should be considered before CRT implantation.

Left ventricular dyssynchrony predicts benefit of cardiac resynchronization therapy in patients with end-stage heart failure before pacemaker implantation

We evaluated patients with end-stage heart failure who have a high likelihood of response to cardiac resynchronization therapy (biventricular pacing). It appears that 20% of patients do not respond to this expensive therapy despite the use of selection criteria (dilated cardiomyopathy, heart failure, New York Heart Association class II or IV, left ventricular ejection fraction <35%, left bundle branch block, and QRS >120 ms). The presence of left ventricular dyssynchrony is needed to result in improvement after cardiac resynchronization therapy.