Elsevier

Heart Failure Clinics

Volume 2, Issue 2, April 2006, Pages 179-192
Heart Failure Clinics

Myocardial Dyssynchrony and Resynchronization

https://doi.org/10.1016/j.hfc.2006.02.001Get rights and content

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Myocardial dyssynchrony in heart failure

Heart failure is a common cardiovascular condition with more than 500,000 new cases each year and requiring close to 1 billion dollars in health care expenses [1]. During the last decade or so, several publications have noted the prevalence and unfavorable effects of conduction abnormalities in heart failure [2], [3], [4], [5]. Conduction delay, most often in the lateral wall, results in early activation and contraction of the septum at a time when the lateral wall is quiescent, and thus in

Response to cardiac resynchronization therapy

Despite strong evidence of clinical and morphologic improvement after CRT, there appear to be a number of eligible patients who do not respond to this invasive and expensive therapy [26]. Indeed, some patients may experience increased morbidity after CRT [27]. In an attempt to develop better strategies for identifying patients who are most likely to respond to CRT, various clinical, electrocardiographic, and imaging techniques have been, and continue to be, explored.

All the major clinical

Mechanical synchrony and cardiac resynchronization therapy response

The fundamental abnormality in heart failure patients corrected by CRT is delay in mechanical activation for territories within the LV chamber. It is probably important that early and late regions exist as territories (ie, lateral or posterior wall versus septum) rather than as microdispersed regions throughout the ventricle. Mechanical dyssynchrony can be visually evident by examining regional wall motion, but it is not obvious in most cases. Mechanical dyssynchrony was examined quantitatively

Conventional echocardiography

Conventional and novel echocardiographic techniques have been used to assess both inter- and intraventricular dyssynchrony. Interventricular dyssynchrony denotes mechanical delay in activation of the right and left ventricle. Normally, both ventricles are synchronized and activate almost simultaneously. In heart failure, delayed LV lateral wall activation results in a significant delay in LV ejection, compared with the right ventricle. This interventricular mechanical delay is assessed most

Tissue Doppler echocardiography

Tissue Doppler echocardiography (TDE) uses the Doppler principle to track tissue (myocardial motion) rather than blood flow [39], [40], [41], employing a pulsed Doppler sample volume or a sample volume within a two-dimensional Doppler sector. Tissue Doppler techniques are used commonly to assess myocardial function in cardiomyopathy and ischemia, and during diastole [42], [43], [44], [45], [46], [47], [48], [49]. This method yields the speed at which a particular portion of myocardium moves and

Strain echocardiography

Tissue velocity measures tissue motion (displacement) at a single point along the ultrasound beam and is therefore susceptible to cardiac translational motion and tethering artifacts. Measurement of strain, on the other hand, depicts regional deformation references typically to diastole, and is less susceptible to such artifacts. Initially, strain was determined noninvasively using MRI [56], [57], but now it can be assessed by TDE as well [58], [59], [60], [61]. Although one might expect strain

Contrast echocardiography

Kawaguchi and colleagues [64] explored the use of echocardiographic contrast to obtain information on regional dyssynchrony. This novel echocardiographic method used contrast variability imaging to quantify dyssynchrony. Thirty to fifty consecutive images of the heart, gated to the cardiac cycle, were obtained before and during contrast injection. At each phase and for each pixel, the temporal average and variance were determined from the total set of cycles. The final pixel intensity was set

Three-dimensional echocardiography

Real-time three-dimensional echocardiography (3DE) uses a matrix array transducer to obtain a real-time pyramidal volume scan of the heart. Because real-time scan volumes are relatively narrow, acquisition of real-time images of the entire heart is facilitated by widening the sector and acquiring images from every other cardiac cycle. This is called a full volume acquisition. For quantitative analysis of dyssynchrony using 3DE, the system defines a number of 2D slices through the voxel-based 3D

MRI

MRI allows detailed interrogation of cardiac structure and function with high spatial resolution and is relatively operator independent. Quantitative MRI-based strain techniques have been used to assess myocardial mechanics [56], [57]. The potential advantages of MRI-based techniques for dyssynchrony assessment include excellent reproducibility, high spatial resolution, and the ability to obtain three-dimensional information, including mechanics, in the circumferential orientation [67]. Recent

Strain-encoded MRI

Strain-encoded (SENC) MRI is a new method of measuring regional strain that requires less complex image processing [73]. As a result, it is faster than HARP analysis, which still requires some postprocessing. SENC imaging is derived from a standard myocardial tagging sequence in which the tissue at end-diastole is tagged with a sinusoidal pattern designed to modulate the longitudinal magnetization orthogonal to the imaging plane. Deformation of tissue during systole will change the local

Dyssynchrony indices by MRI

Given the more comprehensive strain data generally obtained by MRI methods, a number of approaches have been developed to assess 3-D dyssynchrony. The methods are not specific to this imaging approach, however, and can be employed as well using TDE-derived measurements.

The regional variance of strain is determined from the variance of strain magnitude obtained from 28 radially displaced segments for each short-axis section and averaged among slices for each time point. This approach is similar

Summary

Conduction abnormalities are noted in a number of patients with heart failure and are associated with altered ventricular mechanics (mechanical dyssynchrony), resulting in reduced and inefficient systolic function. Correction of mechanical dyssynchrony via biventricular pacing (cardiac resynchronization) is associated with substantial symptomatic benefits, reverse remodeling of the left ventricle, reduced hospitalizations for heart failure, and improved survival. However, approximately 30% of

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      Early attempts to identify objective criteria for “nonresponse” focused on detecting underlying mechanical (either intraventricular or interventricular) dyssynchrony. This appears to be a logical definition of the intended benefits of CRT because inadequate resynchronization (or an absence of underlying dyssynchrony) may lead directly to a lack of intended benefits following CRT.12 In a prospective series of HF patients who failed to show evidence of either clinical and/or echocardiographic responses after at least 3 months of follow-up post-CRT implantation, it was found that not only device-related factors but also substrate-related and logistic-related factors could be identified as contributing to CRT nonresponse (Table 1).13

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