Blood-Tissue Interaction and Ventricular Mechanical Function in Chronic Ischemic Heart Disease

Presenting Author(s)

• JL

  Jennifer M. Li, BSc

  MD Student
  University of Arizona College of Medicine - Phoenix

Primary Author(s)

• JL

  Jennifer M. Li, BSc

  MD Student
  University of Arizona College of Medicine - Phoenix

Co-Author(s)

• MK

  Mary J. Keushkerian, BSc

  Research Assistant
  David Geffen School of Medicine at UCLA and VA Greater Los Angeles Healthcare System
• AP

  Arutyun Pogosyan, MD

  M.D.
  University of California, Los Angeles
• ZM

  Zhengyang Ming, BSc

  B.S.
  University of California, Los Angeles
• MM

  Mostafa Mahmoudi, PhD

  Postdoctoral Scholar
  David Geffen School of Medicine at UCLA and VA Greater Los Angeles Healthcare System
• 

  J. Paul Finn, MD

  Professor
  University of California, Los Angeles
• 

  Xiaodong Zhong, PhD

  Associate Professor
  University of California Los Angeles
• 

  Kim-Lien Nguyen, MD

  Associate Professor of Cardiovascular Medicine and Radiology
  David Geffen School of Medicine at UCLA and VA Greater Los Angeles Healthcare System

Background: Fluid forces are known to play a crucial role in embryonic cardiac morphogenesis, while changes in fluid dynamics have been implicated as the initial mechanical phenomenon in conditions leading to left ventricular (LV) remodeling.¹ Hemodynamic force (HDF) analysis, based on Newton’s third law (action-reaction), provides spatial-temporal representation of intraventricular pressure gradients from interactions between blood volume and endocardial tissue.² Using a modified momentum balance formula based on the first principle of fluid dynamics (conservation of mass), HDF can be calculated from geometric and velocity data derived at the blood volume border.^3,4 We aim to evaluate the relationship between LV ejection fraction (EF), global strain, and HDF in the chronic ischemic heart disease (IHD) population. We hypothesize that relative to healthy controls, patients with IHD have abnormal HDFs.

Methods: In this prospective study, a total of 80 participants underwent CMR at 3T with breath-held balance steady-state free precession (bSSFP) cine imaging, including 30 healthy volunteers (1 male, 29 female; age 29.8±8.8 years) and 50 patients with stress cardiac PET-confirmed IHD (37 male, 13 female; age 66.7±10.4 years). Feature-tracking endocardial global longitudinal (GLS) and circumferential strain (GCS) were calculated. GLS was derived from three long-axis views and GCS was derived from base, mid, and apical short-axis views. LV HDF measurements were computed as root mean square (RMS) percent in the longitudinal [apical-basal (A-B)] and transverse [lateral-septal (L-S)] direction and as the ratio of A-B:L-S during one heartbeat. LVEF was computed using end-diastolic (EDV) and end-systolic volumes (ESV). Group comparisons were performed using Student’s t-tests (p< 0.05 was considered significant).

Results: A-B RMS (12.4% vs 16.6%, p< 0.001), L-S RMS (2.5% vs 3.1%, p=0.011), EF (56.9% vs 62.9%, p=0.002), GLS (18.1% vs 23.4%, p< 0.001), and GCS (31.5% vs 33.5%, p=0.026) were decreased in IHD patients relative to healthy controls (Table 1). Specifically, in IHD patients with EF≥50, A-B RMS was lower (p=0.007). There was no significant difference in L-S RMS (p=0.059). An illustrative example is provided (Fig 1). Average LV ESV (63.6 mL vs 43.8 mL, p=0.001) and EDV (143.1 mL vs 125.6 mL, p=0.014) were higher in IHD patients. Significant positive correlations were noted between global strain and EF. Weaker correlations were observed between HDFs and EF, although still statistically significant.

Conclusion: Chronic IHD is associated with changes in blood-tissue interactions, as evidenced by HDFs. HDF and strain measurements may serve as useful metrics for the noninvasive evaluation of blood-tissue interactions and ventricular mechanical motion in the setting of IHD. Further longitudinal studies are warranted to investigate these parameters in early detection of heart failure and adverse ventricular remodeling.

Left ventricular hemodynamic force and strain analysis for a patient with ischemic heart disease and normal LVEF. (A-F) Long axis bSSFP cine images acquired at 3T with endocardial tracings used for image analysis of HDF and longitudinal strain. The images were from a 79-year-old male with a history of coronary artery disease and prior three-vessel bypass, type 2 diabetes mellitus, and evidence of inducible ischemia in the inferoseptum on a stress cardiac PET scan. Long-axis (LA) derived strain analysis shows (G) a 3D model of the LV with areas of abnormal strain measurements (red) and (H) corresponding 17-segment AHA polar map. (I) Endocardial global longitudinal (red line) and circumferential (pink line) strain-time curves reflect strain evolution (in unit percent) as a function of time in one cardiac cycle. (J) HDF vectors are mapped on a polar grid. (K) HDF plot shows the longitudinal (A-B) and transverse (L-S) forces represented as root-mean-square values vs time in one cardiac cycle.