Four-dimensional blood flow-specific markers of LV dysfunction in dilated cardiomyopathy

Abstract

Aims: Patients with mild heart failure (HF) who are clinically compensated may have normal left ventricular (LV) stroke volume (SV). Despite this, altered intra-ventricular flow patterns have been recognized in these subjects. We hypothesized that, compared with normal LVs, flow in myopathic LVs would demonstrate a smaller proportion of inflow volume passing directly to ejection and diminished the end-diastolic preservation of the inflow kinetic energy (KE).

Methods and results: In 10 patients with dilated cardiomyopathy (DCM) (49 ± 14 years, six females) and 10 healthy subjects (44 ± 17 years, four females), four-dimensional MRI velocity and morphological data were acquired. A previously validated method was used to separate the LV end-diastolic volume (EDV) into four flow components based on the blood's locations at the beginning and end of the cardiac cycle. KE was calculated over the cardiac cycle for each component. The EDV was larger (P = 0.021) and the ejection fraction smaller (P < 0.001) in DCM compared with healthy subjects; the SV was equivalent (DCM: 77 ± 19, healthy: 79 ± 16 mL). The proportion of the total LV inflow that passed directly to ejection was smaller in DCM (P = 0.000), but the end-diastolic KE/mL of the direct flow was not different in the two groups (NS).

Conclusion: Despite equivalent LVSVs, HF patients with mild LV remodelling demonstrate altered diastolic flow routes through the LV and impaired preservation of inflow KE at pre-systole compared with healthy subjects. These unique flow-specific changes in the flow route and energetics are detectable despite clinical compensation, and may prove useful as subclinical markers of LV dysfunction.

Figures

Figure 1

Blood flow component definitions: illustration showing the components defined in Table 2. Direct flow, green; retained inflow, yellow, delayed ejection flow, blue; and residual volume, red. LA, left atrium; LV, left ventricle.

Figure 2

Blood flow visualization: pathline visualization of the four flow components (direct flow, retained inflow, delayed ejection flow, and residual volume). (A–C) a healthy 50-year-old woman with normal LV diastolic function; (D–F) a 62-year-old male with DCM and LV relaxation abnormality; (G–I) a 61-year-old female with DCM and restrictive LV filling. Semi-transparent three-chamber images provide anatomical orientation. Ao, aorta; LA, left atrium; LV, left ventricle.

Figure 3

Blood flow components: blood flow components presented as a percentage of end-diastolic volume (mean ± SD). Top panel: DCM patients (n = 10); lower panel: healthy subjects (n = 10). *Components with a P-value <0.0125 compared with the corresponding component in the healthy group. Intra-group comparison: †P-value ≤0.0002 among DCM patients vs. residual volume. ‡P-value ≤0.005 vs. direct flow in healthy subjects. §P-value =0.000 vs. residual volume in healthy subjects.

Figure 4

Kinetic energy over diastole: for each individual in the study kinetic energy per mL of blood (J/mL) is shown over the diastolic interval, normalized by the length of diastole, left panels: DCM patients; and right panels: healthy subjects. Direct flow (A and B), retained inflow (C and D), delayed ejection flow (E and F), and residual volume (G and H).

Figure 5

Pre-systolic kinetic energy: the kinetic energy (KE) at end-diastole, in mJ/mL, for each flow component in DCM patients (left) and healthy subjects (right). Bars show group mean and standard deviation. *P-value <0.0125 vs. the corresponding component in healthy subjects. Intra-group comparison: †P-value ≤0.0001 vs. direct flow. ‡P-value ≤0.0001 vs. residual volume.

Figure 6

Early vs. late inflow: characteristics of direct flow during early (E) and late (A) diastole. At end-diastole (A) the direct flow volume as a percentage of the total inflow for E and A. The sum of the values at E and A, for each group, gives the direct flow to total inflow ratio for the entire diastolic filling phase (DCM: 46 ± 9% vs. healthy: 70 ± 6%, P = 0.000). (B) The kinetic energy at E and A. Data are presented as mean and standard deviation. (A) *P-value =0.000 for direct flow A in DCM vs. direct flow A in healthy subjects. (B) †P-value =0.003 for direct flow E in healthy subjects vs. direct flow A in healthy subjects.