Degree Of Dyssynchrony Research Articles

Myocardial perfusion and flow reserve in the asynchronous heart: mechanistic insight from a computational model.

The tight coupling between myocardial oxygen demand and supply has been recognized for decades, but it remains controversial whether this coupling persists under asynchronous activation, such as during left bundle branch block (LBBB). Furthermore, it is unclear whether the amount of local cardiac wall growth, following longer lasting asynchronous activation, can explain differences in myocardial perfusion distribution between subjects. For better understanding of these matters, we built upon our existing modeling framework for cardiac mechanics-to-perfusion coupling by incorporating coronary autoregulation. Regional coronary flow was regulated with a vasodilator signal based on regional demand, as estimated from regional fiber stress-strain area. Volume of left ventricular wall segments was adapted with chronic asynchronous activation towards a homogeneous distribution of myocardial oxygen demand per tissue weight. Modeling results show that: (1) both myocardial oxygen demand and supply are decreased in early-activated regions and increased in late-activated regions; (2) but that regional hyperemic flow remains unaffected; while (3) regional myocardial flow reserve (the ratio of hyperemic to resting myocardial flow) decreases with increases in absolute regional myocardial oxygen demand as well as with decreases in wall thickness. These findings suggest that septal hypoperfusion in LBBB represents an autoregulatory response to reduced myocardial oxygen demand. Furthermore, oxygen demand-driven remodeling of wall mass can explain asymmetric hypertrophy and the related homogenization of myocardial perfusion and flow reserve. Finally, the inconsistent observations of myocardial perfusion distribution can primarily be explained by the degree of dyssynchrony, the degree of asymmetric hypertrophy, as well as the imaging modality used.

Association between non-perfusion parameters and presence of ischemia in gated-SPECT myocardial perfusion imaging studies

BackgroundCombined assessment of perfusion and function improves diagnostic and prognostic power of gated-SPECT in patients with coronary artery disease. The aim of this study was to investigate whether the presence of stress-induced ischemia is associated with abnormal resting left ventricular (LV) function and intraventricular dyssynchrony. Methods and ResultsGated-SPECT myocardial perfusion imaging (MPI) at rest and 15 min post-stress was performed in 101 patients, who were divided into three groups: those with stress-induced ischemia (Group 1, n = 58), those with normal scans (Group 2, n = 28), and those with scar but no ischemia (Group 3, n = 15). More extensive perfusion defects were found in patients of Groups 1 and 3 [Summed stress score (SSS): 13 ± 8 and 21 ± 9, respectively]. In Group 2, the mean SSS was 1.5. The mean change in LV ejection fraction (LVEF at stress − LVEF at rest) was higher in Group 1 v. Group 2 patients: −5.54% ± 6.24% vs −2.46% ± 5.56%, p = 0.02. Group 3 patients also had higher values, similar to Group 1: −6.47% ± 8.82%. Patients with ischemia had almost 50% higher end-diastolic volumes than patients with normal MPI. Similarly, end-systolic volumes were almost twice as high in this group (p < 0.0001). In addition, the histogram bandwidth, a measure of intraventricular dyssynchrony, was greater in Group 1. ConclusionsBaseline differences in left ventricular volumes and degree of dyssynchrony are associated with inducible ischemia on stress testing in a gated-SPECT MPI. Stress-induced ischemia increases the degree of intraventricular dyssynchrony.

Mechanical dyssynchrony according to validated cut-off values using gated SPECT myocardial perfusion imaging

BackgroundThe aim of this study was to establish different degrees of mechanical dyssynchrony according to validated cut-off (CO) values of myocardial perfusion gated SPECT phase analysis parameters (SD, standard deviation; B, bandwidth; S, skewness; K, kurtosis). MethodsUsing Emory Cardiac Toolbox™, we prospectively analyzed 408 patients (mean age 64.1 years, 26.7% female), divided into a control group of 150 normal subjects and a validation group of 258 patients (left bundle branch block: 17.8%, right bundle branch block: 8.9%. atrial fibrillation: 16.3%, coronary revascularization: 30%, dilated cardiomyopathy: 7.4%. valvulopathies: 2.7%, ischemic test: 45.3%) with ischemic and non-ischemic cardiac diseases, by means of phase analysis. ResultsAgreement of CO values (SD > 18.4°; B > 51°; S ≤ 3.2; K ≤ 9.3) used to discriminate between normal subjects and patients was strong (c-statistic 0.9; 95% CI 0.98-0.99). Four degrees of dyssynchrony were found according to the number of abnormal phase parameters. All patients with mechanical and electrical criteria for cardiac resynchronization therapy (CCRT) (n: 82) had Grade 2 to 4 (two to four abnormal phase parameters). Agreement of CO values (SD > 40.2°; B > 132°; S ≤ 2.3; K ≤ 4.6) used to discriminate between patients with and without CCRT was strong (c-statistic 0.8; 95% CI 0.79-0.87) but 12% of patients with CCRT did not have any of these abnormal phase parameters. ConclusionsThe discriminatory capacity of gated SPECT phase analysis parameters between normal subjects and patients, and between patients with and without CCRT, is very good, making it possible to define different degrees of mechanical dyssynchrony.

Electrophysiological and Hemodynamic Effects of Vernakalant and Flecainide During Cardiac Resynchronization in Dyssynchronous Canine Hearts

Patients with heart failure and left bundle branch block (LBBB) are frequently treated with biventricular pacing (BiVP). Approximately one-third of them suffer from atrial fibrillation. Pharmacological conversion of atrial fibrillation is performed with drugs that slow ventricular conduction, but the effects of these drugs on the benefit of BiVP are poorly understood. Experiments were performed in dogs with chronic LBBB, investigating the effects of Vernakalant and Flecainide (n = 6 each) on hemodynamics and electrophysiology during epicardial (EPI) and endocardial BiVP. The degree of dyssynchrony and conduction slowing was quantified using QRS width and EPI electrical mapping. Compared with LBBB, EPI and endocardial BiVP reduced QRS duration by 7% ± 9% (P < 0.05 compared with LBBB) and 20% ± 13% (P < 0.05 compared with LBBB, P < 0.05 between modes), respectively. During BiVP, the administration of Vernakalant and Flecainide increased QRS duration by 20% ± 14% (P < 0.05 compared with predrug BiVP) and 34% ± 10% (P < 0.05 compared with predrug BiVP, P < 0.05 between drugs). left ventricular (LV) dP/dtmax decreased by 16% ± 8% (P < 0.05 compared with predrug BiVP) during Vernakalant and by 14% ± 15% (P < 0.05 compared with predrug BiVP) during Flecainide. The drugs did not affect the relative changes in QRS width and LV dP/dtmax induced by BiVP. Vernakalant and Flecainide decrease contractility, slow myocardial conduction velocity, and increase activation time. The electrical and hemodynamic benefits of BiVP are not altered by the drugs.

In This Issue

HomeCirculation ResearchVol. 113, No. 5In This Issue Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBIn This Issue Originally published16 Aug 2013https://doi.org/10.1161/RES.0b013e3182a71457Circulation Research. 2013;113:479Dyssynchrony in Cytosolic Ca2+ Decay (p 527)Download figureDownload PowerPointHeart cells clear up their cytoplasmic calcium somewhat dyssynchronously, say Hohendanner et al, and this dyssynchrony gets worse in failing hearts.Calcium is the major intracellular regulator of cardiomyocyte contraction. It is released from its intracellular storage site, the sarcoplasmic reticulum, into the cytoplasm where it then activates the contractile machinery. But after each contraction, the cell must relax—a process that requires the prompt and efficient removal of calcium from the cytosol. This combined release and clear up of calcium is known as a calcium transient. It has been shown that the release of calcium across the cell is synchronized to ensure coordinated control of the contractile machinery, but less is known about the clean-up, or decay phase. Hohendanner and colleagues now show that calcium removal occurs at different microdomains throughout the cell and that the speed of decay varies from domain to domain. Furthermore, the rate of relaxation at adjacent contractile machinery varies in concordance with the differing decay rates of the domains. They also found that the degree of dyssynchrony is vastly exaggerated in failing human hearts as well as in mice with hypertrophy and pigs with chronic myocardial ischemia. This, increased dyssynchrony slows down the overall rate of relaxation and, the authors suggest that it might contribute to contractile dysfunction associated with cardiac hypertrophy and heart failure.Bone-Derived Stem Cells Repair the Heart (p 539)Download figureDownload PowerPointBelieve it or not, bone stem cells are better than cardiac stem cells for repairing a damaged heart, say Duran et al.While stem cell therapy is a promising approach for repairing damaged hearts, the results obtained to-date have been modest. Part of the problem is that different types of stem cells yield different results and the precise mechanisms underlying the beneficial effects of stem cells remain unclear. Thus, Duran and colleagues examined two mechanisms of repair—differentiation of stem cells into cardiac cell types and secretion of paracrine factors—in two different stem cell types, one from cortical bone and another from the heart. They found that when injected into damaged mouse hearts, the bone cells were actually more adept at differentiating into cardiac cell types—including cardiomyocytes, vascular endothelial cells, and smooth muscle cells—than the heart-derived cells, which only differentiated into immature cardiomyocytes. Cells from the bone also displayed sustained expression of pro-angiogenic paracrine factors, which correlated with better neovascularization of the damaged hearts. Cardiac stem cells, on the other hand, produced similar paracrine factors but only for one day after injection. Importantly, the better performance by the bone cells translated to improved heart function and increased survival for the mice, suggesting that the use of these cells might improve outcomes of cell therapy.IKK2 is a Myosin Light Chain Kinase (p 562)Download figureDownload PowerPointYing et al identify a possible new target for treating hypertension.Constriction of vascular smooth muscle cells (VSMCs), which contributes to hypertension, is controlled in part by phosphorylation of the myosin light chain (MLC). This post-translational modification enables actin and myosin molecules of the contractile machinery to interact and initiate contraction. MLC is known to be phosphorylated by MLCK but recent work suggests that at least one other kinase may be involved. For example, it has been observed that inhibition of MLCK does not lead to the complete dephosphorylation of MLC and that in MLCK-deficient mice, blood vessels remain responsive to vasoconstrictors. In addition, previous work has shown that the kinase IKK2 regulates migration and morphology in mouse embryonic fibroblasts, and that both of these processes depend on MLC phosphorylation. This led Ying and colleagues to ask whether IKK2 could be an MLC kinase in VSMCs. They found that not only was MLC phosphorylated by IKK2 in vitro and but also overexpression of IKK2 in VSMCs led to increased MLC phosphorylation. Conversely, inhibition of IKK2 decreased MLC phosphorylation and attenuated vasoconstrictive responses of isolated rat aortas. Furthermore, mice that lacked IKK2 in their VSMCs showed a decreased hypertensive response to three different vasoconstrictors. These results suggest that IKK2 inhibition could be a novel approach for decreasing hypertension. Previous Back to top Next FiguresReferencesRelatedDetails August 16, 2013Vol 113, Issue 5 Advertisement Article InformationMetrics © 2013 American Heart Association, Inc.https://doi.org/10.1161/RES.0b013e3182a71457 Originally publishedAugust 16, 2013 PDF download Advertisement

Evaluation of changes in left ventricular myocardial function observed in canine myocardial dysfunction model using a two-dimensional tissue tracking technique

This study was conducted to assess the ability of two-dimensional tissue tracking (2DTT) to evaluate changes in left ventricular (LV) myocardial function associated with sustained high electrical pacing. Pacemakers were implanted at the right ventricular (RV) apex of five female Beagles, and sustained high electrical pacing of 250 beats per minute (bpm) was performed for three consecutive weeks. Conventional echocardiography and 2DTT were performed at baseline, and at every week for three weeks with pacing. The baseline parameters were then compared to those of weeks 1, 2, and 3. Three weeks of pacing resulted in significant reduction of radial and circumferential global strains (p < 0.001). Regional analysis revealed reduction of segmental strains in both radial and circumferential directions, as well as increased dyssynchrony after three weeks of pacing in the radial direction (p = 0.0007). The results of this study revealed the ability of 2DTT to measure radial and circumferential strains in dogs with sustained high-electrical pacing, and allowed assessment of global and regional myocardial function and the degree of dyssynchrony.

Correlation between Electrocardiographic Features and Mechanical Dyssynchrony in Heart Failure Patients with Left Bundle Branch Block

Few electrocardiographic parameters beyond the QRS duration were studied with regard to the correlation with mechanical dyssynchrony. This study aims to analyze the correlation between electrocardiographic parameters and mechanical dyssynchrony in patients with symptomatic heart failure (HF) and left bundle branch block (LBBB). Patients with HF, ejection fraction ≤ 35%, and QRS interval ≥ 120 ms with a LBBB were prospectively studied. We analyzed the correlation between electrocardiographic parameters (QRS duration, R voltage in limb leads, S voltage in precordial leads, Sokolow and Cornell indexes, QRS axis deviation, and QRS notches in lateral and inferior leads) and mechanical dyssynchrony measured by tissue Doppler imaging (TDI). A group of 50 patients were studied, 60% male, 78% with nonischemic cardiomyopathy, NYHA Class III-IV (86%), and ejection fraction of 0.22 ± 0.6. Intra- and interventricular dyssynchrony occurred in 68% and 74% of patients, respectively. The S amplitude in precordial leads and the Sokolow and Cornel indexes show a weak correlation with the degree of dyssynchrony. In the patients with QRS notching in the lateral and inferior leads, we observed significantly greater prevalence of intraventricular dyssynchrony, with sensitivity and specificity of 85% and 56%, respectively, for notches in lateral leads. The QRS duration presents moderate correlation with the degree of both intraventricular (r = 0.48) and interventricular dyssynchrony (r = 0.46). The following electrocardiographic parameters were related to the degree of mechanical dyssynchrony: QRS duration and notches in QRS. In addition, the patients tend to have highest S amplitude in precordial leads.

Relation of left-ventricular dyssynchrony by phase analysis of gated SPECT images and cardiovascular events in patients with implantable cardiac defibrillators

BackgroundLeft-ventricular (LV) dyssynchrony could be measured by gated SPECT myocardial perfusion imaging (MPI). This study examined the relation between the degree of dyssynchrony and outcome in patients with implantable cardiac defibrillators (ICDs). Methods and ResultsWe studied 70 patients with ICD and LV ejection fraction (EF) <.40 by gated MPI (performed within 6 weeks of the device implantation). The images were re-processed using phase analysis to derive phase standard deviation (SD) and histogram bandwidth. All-cause mortality and appropriate ICD shocks were identified as the primary endpoint. There were 87% men, aged 62 ± 11 years. The EF was 26 ± 8% (range 12%-39%). The phase SD was 51° ± 20° (range 12°-99°) and the histogram bandwidth was 157° ± 72° (range 21°-327°). The SD and bandwidth were significantly greater than corresponding values in patients with normal EF (15.8 ± 11.8° and 42.0 ± 28.4°, respectively, P < .0001, each). At 1 year, 8 patients (11%) died or had shocks. The patients with events had higher phase SD than those without events (60 ± 5° vs 50 ± 21°, P = .002). The histogram bandwidth was also higher in those with events (185 ± 37 vs 154 ± 75, P = .07). All patients with event had a phase SD ≥ 50°, while none of the patients with a phase SD < 50° (N = 26) had an event (P = .02). ConclusionsThe severity of LV dyssynchrony by phase analysis in patients with LV dysfunction, and ICD is associated with increased risk of death and appropriate ICD shock; a phase SD < 50° was associated with no events at 1 year.

RELATION OF LEFT VENTRICULAR DYSSYNCHRONY BY PHASE ANALYSIS OF GATED SPECT IMAGES AND CARDIOVASCULAR EVENTS IN PATIENTS WITH IMPLANTABLE CARDIAC DEFIBRILLATORS.

Background Left-ventricular (LV) dyssynchrony could be measured by gated SPECT myocardial perfusion imaging (MPI). This study examined the relation between the degree of dyssynchrony and outcome in patients with implantable cardiac defibrillators (ICDs).

Evaluation of the effects of transvenous pacing site on left ventricular function and synchrony in healthy anesthetized dogs

OBJECTIVE-To compare the acute effects of cardiac pacing from various transvenous pacing sites on left ventricular (LV) function and synchrony in clinically normal dogs. ANIMALS-10 healthy adult mixed-breed dogs. PROCEDURES-Dogs were anesthetized, and dual-chamber transvenous biventricular pacing systems were implanted. Dogs were paced in single-chamber mode from the right atrial appendage (RAA) alone and in dual-chamber mode from the right ventricular apex (RVA), from the left ventricular free wall (LVFW), and simultaneously from the RVA and LVFW (BiV). Standard ECG and echocardiographic measurements, cardiac output measured with the lithium dilution method (LiDCO), and tissue Doppler-derived measurements of LV synchrony were obtained during each of the pacing configurations. RESULTS-Placement of the biventricular pacing systems was possible in 8 of the 10 dogs. The QRS duration was significantly different among all pacing sites, and the order of increasing duration was RAA, BiV, LVFW, and RVA. Pacing sites did not differ with respect to fractional shortening; however, pacing from the RVA resulted in a significantly lower ejection fraction than pacing from all other sites. During RVA and LVFW pacing, LiDCO was significantly lower than that at other sites; there was no significant difference between RAA and BiV pacing with respect to LiDCO. Although the degree of dyssynchrony was significantly lower during pacing from the RAA versus other ventricular pacing sites, it was not significantly different among sites. CONCLUSIONS AND CLINICAL RELEVANCE-Ventricular activation by RAA pacing provided the best LV function and synchrony. Pacing from the RVA worsened LV function, and although pacing from the LVFW improved it, BiV pacing may provide additional improvement.

The effects of aetiology on outcome in patients treated with cardiac resynchronization therapy in the CARE-HF trial.

AimsCardiac dyssynchrony is common in patients with heart failure, whether or not they have ischaemic heart disease (IHD). The effect of the underlying cause of cardiac dysfunction on the response to cardiac resynchronization therapy (CRT) is unknown. This issue was addressed using data from the CARE-HF trial.Methods and resultsPatients (n = 813) were grouped by heart failure aetiology (IHD n = 339 vs. non-IHD n = 473), and the primary composite (all-cause mortality or unplanned hospitalization for a major cardiovascular event) and principal secondary (all-cause mortality) endpoints analysed. Heart failure severity and the degree of dyssynchrony were compared between the groups by analysing baseline clinical and echocardiographic variables. Patients with IHD were more likely to be in NYHA class IV (7.5 vs. 4.0%; P = 0.03) and to have higher NT-proBNP levels (2182 vs. 1725 pg/L), indicating more advanced heart failure. The degree of dyssynchrony was more pronounced in patients without IHD (assessed using mean QRS duration, interventricular mechanical delay, and aorta-pulmonary pre-ejection time). Left ventricular ejection fraction and left ventricular end-systolic volume improved to a lesser extent in the IHD group (4.53 vs. 8.50% and −35.68 vs. –58.52 cm3). Despite these differences, CRT improved all-cause mortality, NYHA class, and hospitalization rates to a similar extent in patients with or without IHD.ConclusionThe benefits of CRT in patients with or without IHD were similar in relative terms in the CARE-HF study but as patients with IHD had a worse prognosis, the benefit in absolute terms may be greater.

Similar Degree in Mechanical Left Ventricular Dyssynchrony Between Right Ventricular Outflow Tract and Right Ventricular Apical Pacing: A Strain Doppler Imaging Study

Background and Objectives: Long-term right ventricular (RV) apex pacing has been associated with left ventricular (LV) systolic dysfunction. However, pacing in the RV outflow tract (RVOT) is associated with a narrower QRS duration and may have a more normal LV activation in comparison to RV apical (RVA) pacing. We hypothesized that RVOT pacing is associated with less mechanical dyssynchrony compared to RVA pacing and that it also more closely resembles mechanical activation in normal controls with a narrow QRS. Subjects and Methods: We studied 9 patients with RV pacing, 9 with left bundle branch block (LBBB), and 15 normal controls with a narrow QRS. In the RV pacing group, we paced from the RVA and RVOT. At the end of each pacing train, we obtained echocardiographic images in the apical 4- and 2-chamber views and obtained the following parameters: the compression/expansion crossover point (CEP) for myocardial strain and the time from QRS onset to the CEP in the strain image. The degree of dyssynchrony was evaluated using the dispersion and standard deviation of CEP times in 12 segments of the LV. Results: Significant dyssynchrony was observed in the RVOT pacing group compared to the group with normal QRS. No significant difference was observed in LV mechanical dyssynchrony among the RVOT pacing, RVA pacing, and LBBB groups. Conclusion: RVOT pacing is associated with significant LV dyssynchrony. Although the RVOT has been recommended as an alternative site for pacing, this approach may have adverse effects on long-term LV function. (Korean Circ J 2008;38:590-595)

Abstract 2125: Severity of Left Ventricular Dyssynchrony in Patients with Ischemic and Non-Ischemic Cardiomyopathy: a Cardiovascular Magnetic Resonance Tissue Synchronization Mapping Study

Aims: Studies on cardiac resynchronization therapy (CRT) for heart failure have shown a differential response in patients with ischemic (ICM) and non-ischemic cardiomyopathy (NICM). Increasing dyssynchrony has been shown to relate to a poor prognosis in patients with heart failure. We hypothesized that ICM and NICM have varying effects on left ventricular (LV) synchrony. Methods: The recently described cardiovascular magnetic resonance tissue synchronization index (CMR-TSI), which predicts benefit from CRT, was quantified in 181 patients (age: 66.4 ± 10.6 yrs, NYHA class III or IV, LVEF: 23.5 ± 10.8%, QRS = 139.8 ± 32.0 ms) with ICM (n=105) or NICM (n=76) and age-matched, healthy controls (n=24). The maximum time-to-peak radial wall motion in a short axis stack of LV images (steady-steady free precession imaging) was fitted to an empirical sine wave [y = a + b * sin (t/RR + c)]. The CMR-TSI was calculated as the SD of all segmental phase shifts of the radial wall motion extracted from this wave (see Figure for bull’s eye maps). Results: CMR-TSI was higher in ICM (105.8 ± 44.2, ANOVA p&lt;0.0001) and in NICM (68.1 ± 30.5, p&lt;0.0001) than in controls (22.5 ± 8.6) (see Figure ). In multivariate analyses including ICM and NICM patients only, ischemic aetiology emerged as a positive predictor of CMR-TSI, independent of QRS duration, LV end-systolic and end-diastolic volumes, and LVEF (all p&lt;0.0001). Conclusions: ICM is associated with a greater degree of dyssynchrony than NICM, independently of QRS duration, LV volumes and LVEF. These findings may account for the differential response to CRT observed with patients with ICM and NICM.

Relationship between Mechanical Dyssynchrony as Measured by Phase Analysis of Gated SPECT Perfusion Imaging and Cardiac Structure and Function

Introduction: Cardiac resynchronization therapy (CRT) is used for the treatment of patients with advanced heart failure. However, 30% of patients fail to benefit. More precise measurements of dyssynchrony may improve patient selection for CRT. A new method to quantify dyssynchrony has been described using phase analysis of gated SPECT perfusion imaging. The objective of this study is to describe the relationship between the phase analysis indices used to quantify dyssynchrony and left ventricular ejection fraction (LVEF), end-systolic volume (ESV), and mass. Hypothesis: The degreee of dyssynchrony will negatively correlate with LVEF and positively correlate with ESV and mass. Methods: We developed a Fourier analysis method to convert the regional myocardial counts from the discrete frames per cardiac cycle into a continuous thickening function which allows fine temporal resolution of the phase of the onset of myocardial thickening and its corresponding amplitude. Five indices are used to describe the dispersion of the regional left ventricular timing of the onset of mechanical contraction including peak phase, phase standard deviation (SD), bandwidth, skewness, and kurtosis. We evaluated the correlation of these indices with LVEF, ESV, and mass in 200 subjects (left ventricular dysfunction, n = 125; normal controls, n = 75) Results: Phase SD, bandwidth, skewness, and kurtosis demonstrated moderate correlation with LVEF with correlation coefficients of -0.71, -0.69, 0.74, and 0.62 respectively. Phase SD, bandwidth, skewness, and kurtosis demonstrated moderate correlation with ESV with correlation coefficients of 0.71, 0.66, -0.67, and -0.54 respectively. Phase SD, bandwidth, skewness, and kurtosis demonstrated moderate correlation with left ventricular mass with correlation coefficients of 0.66, 0.62, -0.67, and -0.56 respectively. Peak phase did not correlate with LVEF, ESV, or left ventricular mass with correlation coefficients of -.03, -.05, and -0.07 respectively. Conclusions: The degree of dyssynchrony is negatively correlated with LVEF and positively correlated with ESV and mass. Phase SD, bandwidth, skewness, and kurtosis used to quantify dyssynchrony have moderately strong correlations with left ventricular ejection fraction, end-systolic volume, and mass.

Assessment of ventricular dyssynchrony: global or regional function?

A common cliche states that if you stand still every 10 years, you will find yourself in the forefront of fashion. Thus it seems with the analysis of ventricular function. It has been recognized for many years that incoordinate or non-uniform contraction reduces global left ventricular (LV) function. Wiggers demonstrated in 1922 that stimulation from a ventricular focus rather than supraventricular produced a reduced pulse pressure, prolonged isometric contraction, and systolic ejection time in normal hearts. Although regional wall motion abnormalities were recognized early in ischaemic heart disease, it was also demonstrated later that it occurs in dilated or hypertrophic cardiomyopathy.1 However, the realization that asynchronous wall motion due to delayed activation such as in the presence of a left bundle branch block profoundly affected global function did not take place until more recently.2 Developments in cardiac imaging have allowed us to appreciate how common delayed activation and dyssynchronous mechanical contraction are and the degree to which they affect overall ventricular efficiency. Even in the normal heart, there is some degree of dyssynchrony;3 and the normal QRS duration reduces with sympathetic stimulation, implying greater synchrony so that some of the improvement in ‘contractility’ is actually due to a reduction in asynchrony. In the original studies on contractility, the possibility of incoordination was never considered. In disease states, asynchronous activation has marked deleterious effects on ventricular pump function due to both inter- and intra-ventricular asynchrony, leading to prolonged contraction, reduced ejection time, delayed and prolonged relaxation, and reduced diastolic filling time. Lack of coordination between the two papillary muscles also creates mitral regurgitation, and the overall result is LV remodelling with increasing ventricular cavity volumes and a … *Corresponding author. Tel: +44 178255234; fax: +44 1782713071. E-mail address : john.sanderson{at}uhns.nhs.uk

510 Similar degree of mechanical left ventricular dyssynchrony between RV outflow tract and apex pacing for permanent pacemaker site: studied by strain Doppler image

Purpose: The long term right ventricular (RV) apex pacing has been associated with left ventricular (LV) systolic dysfunction. These may be the result of abnormal myocardial shearing forces and stress vectors. However, in RV outflow tract (RVOT) pacing ventricular activation may not be changed from that occurring over the normal His-Purkinje network to that originating from site of the ventricular lead. So we hypothesized that the degree of mechanical LV dyssynchrony in RVOT pacing is less than that in RV apex pacing. Methods: We enrolled 15 controls, 9 patients with RV pacing and 9 patients with LBBB. In RV pacing group, we paced at 2 sites (RV apex and RVOT) with 500 msec for 3 minutes. At the end of each pacing, we had the echocardiographic images in the apical 4 and 2 chamber views. We measured the time from QRS onset to compression/expansion crossover point in the strain image. The degree of dyssynchrony was evaluated by the difference between the longest and shortest parameters. We compared mechanical dyssynchrony in 12 segment of LV among different groups. Results: The degree of mechanical dyssynchrony was similar in RV apical, RVOT pacing and LBBB groups (figure 1). Detailed data are in the table. Conclusion: The RVOT pacing, though it may be recommended as an alternative site, might have an adverse effect on long term LV function.