Assessment of left ventricular mechanical dyssynchrony by phase analysis of ECG-gated SPECT myocardial perfusion imaging

Cardiac resynchronization therapy (CRT) has shown benefits in patients with severe heart failure. However, at least 30% of patients selected for CRT by use of traditional criteria (New York Heart Association class III or IV, depressed left ventricular [LV] ejection fraction, and prolonged QRS duration) do not respond to CRT. Recent studies with tissue Doppler imaging have shown that the presence of LV dyssynchrony is an important predictor of response to CRT. Phase analysis has been developed to allow assessment of LV dyssynchrony by gated single photon emission computed tomography myocardial perfusion imaging. This technique uses Fourier harmonic functions to approximate regional wall thickness changes over the cardiac cycle and to calculate the regional onset-of-mechanical contraction phase. Once the onset-of-mechanical contraction phases are obtained 3-dimensionally over the left ventricle, a phase distribution map is formed that represents the degree of LV dyssynchrony. This technique has been compared with 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.     

实时三维超声心动图评价三支冠脉病变患者左室收缩非同步性

目的:探讨实时三维超声心动图(RT3DE)评价冠心病三支冠状动脉病变患者左心室的收缩非同步性。方法:应用实时三维超声心动图对20例经选择性冠状动脉造影证实的三支冠状动脉病变患者左室同步性指标进行研究,并与20例正常人进行比较。结果:与对照组相比,病例组LVEDV、Tmsv16-SD、Tmsv16-Dif、Tmsv16-SD%、Tmsv16-Dif%显著增加。结论:冠心病三支血管病变左室收缩不同步;实时三维超声心动图检查对冠心病三支病变的左室收缩同步性有重要价值。     

MRI assessment of pacing induced ventricular dyssynchrony in an isolated human heart

This study demonstrates the capabilities of MRI in the assessment of cardiac pacing induced ventricular dyssynchrony, and the findings support the need for employing more physiological pacing. A human donor heart deemed non‐viable for transplantation, was reanimated using an MR compatible, four‐chamber working perfusion system. The heart was imaged using a 1.5T MR scanner while being paced from the right ventricular apex (RVA) via an epicardial placed lead. Four‐chamber, short‐axis, and tagged short‐axis cines were acquired in order to track wall motion and intramyocardial strain during pacing. The results of this study revealed that the activation patterns of the left ventricle (LV) during RVA pacing demonstrated intraventricular dyssynchrony; as the left ventricular mechanical activation proceeded from the septum and anterior wall to the lateral wall, with the posterior wall being activated last. As such, the time difference to peak contraction between the septum and lateral wall was ～125 msec. Likewise, interventricular dyssynchrony was demonstrated from the four‐chamber cine as the time difference between the peak LV and RV free wall motion was 180 msec. With the ongoing development of MR safe and MR compatible pacing systems, we can expect MRI to be added to the list of imaging modalities used to optimize cardiac resynchronization therapy (CRT) and/or alternate site pacing. J. Magn. Reson. Imaging 2010; 31: 466–469. © 2010 Wiley‐Liss, Inc.     

Angiographic and anatomical features of subvalvar left ventricular outflow obstruction in transposition of the great arteries

Left ventricular angiocardiograms were examined from a series of patients with transposition of the great arteries (TGA). Forty-one patients with systolic pressure gradients of 15 mm Hg or more between the left ventricle and pulmonary artery were selected. Seventeen of these had the combination of a pressure gradient at subvalvar level and characteristic angiographic findings. In the anteroposterior projection, there was a persistent, irregular, linear radiolucency in the region of the mitral valve during systole. It was probably produced by the close apposition of the face of the closed mitral valve leaflets to an accentuated bulge of the interventricular septum. Two of the 17 patients subsequently died. Both hearts had endocardial fibrous thickening of the septum at the predicted site of apposition. It is suggested that in TGA the small afterload caused by a relatively low pulmonary vascular resistance may contribute to exaggerated left ventricular emptying, and that this favours mitral-septal apposition.     

Pulmonary arterial hypertension: the key role of echocardiography

Given the nonspecific nature of its early symptoms and signs, pulmonary arterial hypertension (PAH) is often diagnosed in its advanced stages. Although clinical assessment is essential when initially evaluating patients with suspected PAH, echocardiography is a key screening tool in the diagnostic algorithm. It not only provides an estimate of pulmonary pressure at rest and during exercise, but it may also help to exclude any secondary causes of pulmonary hypertension, predict the prognosis, monitor the efficacy of specific therapeutic interventions, and detect the preclinical stage of the disease.     

An early phase of slow myocardial activation may be necessary in order to benefit from cardiac resynchronization therapy

Background

Not all patients with a QRS duration longer than 140 milliseconds respond to cardiac resynchronization therapy (CRT). The same QRS duration may correspond to different spatiotemporal patterns of myocardial activation that influence response to CRT.

Methods

Electrocardiographic ima'ging based on 80 chest wall electrodes was used to construct the spatiotemporal myocardial activation map in 46 consecutive patients before CRT. The cumulative percentage of myocardium activated was plotted against time expressed in terms of quintiles of the overall QRS duration. Changes in the left ventricular ejection fraction and end-diastolic diameter, maximum oxygen consumption per minute, brain natriuretic peptide level, and 6-minute walk distance after 6 months of CRT were compared across different patterns with 1-way analysis of variance.

Results

Data from 34 patients were available for analysis. Four spatiotemporal patterns of myocardial activation could be identified: triphasic (fast-slow-fast) (13), uniform (8), fast-slow (7), and slow-fast (6). The overall QRS duration was similar in the 4 groups (166 ± 19 vs 138 ± 21 vs 157 ± 26 vs 152 ± 37 milliseconds, P = not significant [NS]). The ejection fraction showed a trend of greater increases for the triphasic (6.5% ± 7.0%) and slow-fast (15.5% ± 6.4%) patterns than for the uniform (4.0% ± 13.3%) and fast-slow (8.0% ± 6.1%) patterns (P = NS). The end-diastolic diameter showed a trend of greater decreases for the triphasic (−3.7% ± 5.3%) and slow-fast (−7.0% ± 6.7%) patterns than for the uniform (0.8% ± 6.7%) and fast-slow (0.0% ± 4.6%) patterns (P = NS). The maximum oxygen consumption per minute showed a trend of greater increases for the triphasic (1.2 ± 4.2 mL/kg/min) and slow-fast (4.1 ± 2.7 mL/kg/min) patterns than for the uniform (0.1 ± 4.1 mL/kg/min) and fast-slow (1.0 ± 2.1 mL/kg/min) patterns (P = NS). The brain natriuretic peptide level decreased significantly more for the triphasic (−450 ± 1269) and slow-fast (−3121 ± 1512) patterns than for the uniform (762 ± 1036) and fast-slow (718 ± 2530) patterns (P = .0003). The 6-minute walk distance increased significantly more for the triphasic (29 ± 89) and slow-fast (40 ± 23) patterns than for the uniform (6 ± 87) and fast-slow (37 ± 45) patterns (P = .0003).

Conclusions

Different spatiotemporal patterns of myocardial activation exist among patients with broad QRS complex and may affect response to CRT. An early phase of slow myocardial activation (the triphasic fast-slow-fast and the slow-fast patterns) may be necessary for a patient to benefit from CRT.     

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 ≤ 35%, QRS duration > 120 ms, and intraventricular asynchronism ≥ 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 ≥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. (Echocardiography 2010;27:50-57)