Imaging of myocardial dyssynchrony in congestive heart failure

Assessment of dyssynchrony by gated myocardial perfusion imaging does not improve patient management

Clinical trials have demonstrated improved outcomes with cardiac resynchronization therapy in patients with heart failure and electrical evidence of dyssynchrony. There has been intense effort at developing imaging markers of dyssynchrony with the aim of improved risk stratification. However, these efforts have not been fruitful to date. This article discusses mechanisms of cardiac dyssynchrony, reviews clinical data supporting resynchronization therapy, and addresses the lack of convincing evidence to support the use of noninvasive imaging measures of dyssynchrony in improving patient management.

Mechanical dyssynchrony alters left ventricular flow energetics in failing hearts with LBBB: a 4D flow CMR pilot study

The impact of left bundle branch block (LBBB) related mechanical dyssynchrony on left ventricular (LV) diastolic function remains unclear. 4D flow cardiovascular magnetic resonance (CMR) has provided reliable markers of LV dysfunction: reduced volume and kinetic energy (KE) of the portion of LV inflow which passes directly to outflow (Direct Flow) has been demonstrated in failing hearts compared to normal hearts. We sought to investigate the impact of mechanical dyssynchrony on diastolic function by comparing 4D flow in myopathic LVs with and without LBBB. CMR data were acquired at 3 T in 22 heart failure patients; 11 with LBBB and 11 without LBBB matched according to several demographic and clinical parameters. An established 4D flow analysis method was used to separate the LV end-diastolic (ED) volume into functional flow components based on the blood’s timing and route through the heart cavities. While the Direct Flow volume was not different between the groups, the KE possessed at ED was lower in LBBB patients (P = 0.018). Direct Flow entering the LV during early diastolic filling possessed less KE at ED in LBBB patients compared to non-LBBB patients, whereas no intergroup difference was observed during late filling. Pre-systolic KE of LV Direct Flow was reduced in patients with LBBB compared to matched patients with normal conduction. These intriguing findings propose that 4D flow specific measures can serve as markers of LV mechanical dyssynchrony in heart failure patients, and could possibly be investigated as predictors of response to cardiac resynchronization therapy.

Speckle tracking in the evaluation of left ventricular dyssynchrony

A number of echocardiographic techniques have been introduced to determine left ventricular dyssynchrony (LVD) and to improve selection of patients for CRT. During the last years tissue Doppler imaging (TDI) has been used as the most preferred technique to quantify LVD, but results with nonresponder rates below 30% have been shown only in small studies based on high experience. Angle of incidence dependency, noise, artifacts, and tethering motion of adjacent segments are the main limitations of TDI influencing selection of patients for CRT. Although strain TDI is not affected by translation or tethering, accurate measurement of regional strain is also limited. Two-dimensional (2D) strain imaging based on novel speckle tracking echocardiography (STE) is a relatively new tool to define regional myocardial strain and to quantify dyssynchrony based on a more robust technique and avoiding angle of incidence. Current studies are promising to use strain or vector velocity imaging derived from STE for qualitative and quantitative assessment of LVD and follow-up studies as well. If one compare different types of strain components at present, radial strain imaging seems to be the most promising technique to determine LVD and to predict positive response to CRT. Furthermore, STE offers an insight into rotational mechanics of the dyssynchronous ventricle. Although clinical studies using 2D strain have analyzed LVD related to various conditions, measures are based on a 2D data set. Three-dimensional strain imaging, based on speckle tracking will probably open a new door to assess patients with heart failure and LVD.

Feasibility and initial experience of assessment of mechanical dyssynchrony using cardiovascular magnetic resonance and semi-automatic border detection

BACKGROUND

The systolic dyssynchrony index (SDI) has been introduced as a measure of mechanical dyssynchrony using three-dimensional echocardiography to select patients who may benefit from cardiac resynchronization therapy (CRT). However, three-dimensional echocardiography may be inadequate in a number of patients with suboptimal acoustic window and no single echocardiographic measure of dyssynchrony has proven to be of value in selecting patients for CRT. Thus, the aim of this study was to determine the value of cardiovascular magnetic resonance (CMR) for the assessment of the SDI in patients with reduced LV function as well as in healthy controls using semi-automatic border tracking.

METHODS

We investigated a total of 45 patients including 35 patients (65 +/- 8 years) with reduced LV function (EF 30 +/- 11%) and a wide QRS complex as well as 10 control subjects (42 +/- 21 years, EF 70 +/- 11%). For cine imaging a standard SSFP imaging sequence was used with a temporal resolution of 40 frames per RR-interval. Quantitative analysis was performed off-line using a software prototype for semi-automatic border detection. Global volumes, ejection fraction and the SDI were calculated in each subject. SDI was compared with standard echocardiographic parameters of dyssynchrony.

RESULTS

The mean SDI differed significantly between patients (14 +/- 5%) and controls (5 +/- 2%, p < 0.001). An exponential correlation between the EF and the SDI was observed (r = -0.84; p < 0.001). In addition, a significant association between the SDI and the standard deviation of time to peak systolic motion of 12 LV segments (Ts-SD) determined by echocardiography was observed (r = 0.66, p = 0.002).

CONCLUSION

The results of this preliminary study suggest that CMR with semi-automatic border detection may be useful for the assessment of mechanical dyssynchrony in patients with reduced LV function.

Emerging role of myocardial perfusion imaging to evaluate patients for cardiac resynchronization therapy

Left ventricular (LV) dyssynchrony is an increasingly important consideration in the evaluation and management of patients with LV systolic dysfunction. Improvements in clinical status, LV remodeling, and survival have been demonstrated with the use of cardiac resynchronization therapy (CRT). The current selection criteria for patients who undergo CRT include the presence of severe LV dysfunction, significant heart failure symptoms, and electrical dyssynchrony on surface electrocardiography (wide QRS interval). However, up to 40% of patients who undergo CRT do not experience reductions in symptoms or LV functional improvement. Because electrical dyssynchrony is not synonymous with contractile or mechanical dyssynchrony, efforts have been made to more accurately quantify mechanical dyssynchrony in the hope of improving the selection of patients for CRT. These efforts have focused largely on echocardiographic measures of mechanical dyssynchrony. A novel method to quantify LV mechanical dyssynchrony has been developed using phase analysis of gated single photon-emission computed tomographic myocardial perfusion imaging. In conclusion, this report describes potential advantages, compared with other methods, of using myocardial perfusion imaging to evaluate patients for CRT; reviews the method of the phase analysis technique to quantify dyssynchrony; reviews the available evidence of its utility; and describes future directions in research.