Circumferential myocardial strain in cardiomyopathy with and without left bundle branch block

Abstract

Background: Cardiac resynchronization therapy (CRT) has been shown to decrease mortality in 60-70% of advanced heart failure patients with left bundle branch block (LBBB) and QRS duration > 120 ms. There have been intense efforts to find reproducible non-invasive parameters to predict CRT response. We hypothesized that different left ventricular contraction patterns may exist in LBBB patients with depressed systolic function and applied tagged cardiovascular magnetic resonance (CMR) to assess circumferential strain in this population.

Methods: We determined myocardial circumferential strain at the basal, mid, and apical ventricular level in 35 subjects (10 with ischemic cardiomyopathy, 15 with non-ischemic cardiomyopathy, and 10 healthy controls). Patterns of circumferential strain were analyzed. Time to peak systolic circumferential strain in each of the 6 segments in all three ventricular slices and the standard deviation of time to peak strain in the basal and mid ventricular slices were determined.

Results: Dyskinesis of the anterior septum and the inferior septum in at least two ventricular levels was seen in 50% (5 out of 10) of LBBB patients while 30% had isolated dyskinesis of the anteroseptum, and 20% had no dyskinesis in any segments, similar to all of the non-LBBB patients and healthy controls. Peak circumferential strain shortening was significantly reduced in all cardiomyopathy patients at the mid-ventricular level (LBBB 9 +/- 6%, non-LBBB 10 +/- 4% vs. healthy 19 +/- 4%; both p < 0.0001 compared to healthy), but was similar among the LBBB and non-LBBB groups (p = 0.20). The LBBB group had significantly greater dyssynchrony compared to the non-LBBB group and healthy controls assessed by opposing wall delays and 12-segment standard deviation (LBBB 164 +/- 30 ms vs. non-LBBB 70 +/- 17 ms (p < 0.0001), non-LBBB vs. healthy 65 +/- 17 ms (p = 0.47)).

Conclusions: Septal dyskinesis exists in some patients with LBBB. Myocardial circumferential strain analysis enables detailed characterization of contraction patterns, strengths, and timing in cardiomyopathy patients with and without LBBB.

Figure 1

CSPAMM images of mid ventricular short axis slice and analysis model. A. Tags at the beginning of systole after ECG triggering. B. Same slice at end systole. C. Same slice at diastole with good persistence of tags. D and E show an example of CSPAMM images with the analysis model. D. In early systole, the epicardial border was manually drawn in green, endocardial border in red, superior right ventricular insertion site marked with a yellow triangle, and inferior insertion site marked with a blue triangle. The red donut is the analysis model with the myocardium partitioned in epi-myocardial, mid-myocardial, and endo-myocardial thirds shown in early systole in D and end-systole in E. Magenta dot is the center of the epicardial contour.

Figure 2

Three different septal circumferential strain patterns in patients with LBBB. AVO marks the opening of aortic valve and AVC marks the closure of aortic valve. A. Type Ia. Dyskinesis of the anteroseptum. Inferoseptum ε_cc shortening is reduced. B. Corresponding ECG, QRS = 154 ms. C. Type Ib. Dyskinesis of the entire septum. D. Corresponding ECG, QRS = 150 ms. E. Type II. No dyskinesis but reduced septal ε_cc. F. Corresponding ECG, QRS = 156 ms. Arrows point to presystolic contraction. AS = anteroseptum, IS = inferoseptum, and IL = inferolateral wall. AVO = aortic valve opening. AVC = aortic valve closure.

Figure 3

Septal circumferential strain pattern in patients with non-LBBB (A, B) and healthy (C) subjects. All subjects had normal contraction patterns with maximum negative circumferential strain reached in the septum earlier than in the inferolateral wall. A. Patient with interventricular conduction delay and QRS duration of 146 ms. B. Patient with a normal QRS duration of 98 ms. C. Healthy subject with a normal QRS duration of 98 ms. AS = anteroseptum, IS = inferoseptum, IL = inferolateral wall. AVO = aortic valve opening. AVC = aortic valve closure.

Figure 4

All three types of septal contraction pattern can be observed in both ischemic (ICM) and non-ischemic (non-ICM) cardiomyopathy patients. In LBBB Type Ia, only the anteroseptum is dyskinetic. In LBBB Type Ib, both anteroseptum and inferoseptum are dyskinetic. In LBBB Type II, neither anteroseptum nor inferoseptum is dyskinetic. AS = anteroseptum, IS = inferoseptum.

Figure 5

Circumferential shortening magnitude in three ventricular slices. Compared to healthy controls, both the LBBB and non-LBBB patients have overall significantly reduced ε_cc %S in mid and apical ventricular slices. In the basal slice, non-LBBB patients had significantly reduced ε_cc %S compared to healthy controls but not the LBBB patients. %S = % shortening.