Underlying mechanical efficiency after myocardial infarction (RF_TH_151)

Presenting Author(s)

• MH

  Markus B. Harbo, MD

  PhD fellow
  Oslo University Hospital & University of Oslo, Norway

Primary Author(s)

• MH

  Markus B. Harbo, MD

  PhD fellow
  Oslo University Hospital & University of Oslo, Norway

Co-Author(s)

• KB

  Kjersti Blom

  Dr.
  Oslo University Hospital and University of Oslo, Oslo, Norway, Norway
• YR

  Yasmin D.M. Reyes, MD

  PhD fellow
  Oslo University Hospital & University of Oslo, Norway
• VR

  Vigdis Rosseland

  Radiographer
  Oslo University Hospital, Oslo, Norway., Norway
• TS

  Tryggve Holck Storås, PhD, MSc

  MR Physicist
  Oslo University Hospital, Norway
• NK

  Nils Einar Kløw

  Dr.
  Oslo University Hospital, Ullevål, Oslo, Norway., Norway
• JB

  Jon Arne Birkeland

  Dr.
  Oslo University Hospital, Ullevål, Oslo, Norway., Norway
• GA

  Geir Ø. Andersen, MD, PhD

  Senior Consultant
  Oslo University Hospital, Norway
• IS

  Ivar Sjaastad, MD, PhD

  Dr.
  Oslo University Hospital and University of Oslo, Oslo, Norway, Norway
• EE

  Emil KS Espe

  Dr.
  Oslo University Hospital and University of Oslo, Oslo, Norway, Norway

Fig 1. Millidomain myocardial work. a) We performed cine (i), late gadolinium enhancement (ii), and advanced motion encoding tissue phase mapping (TPM (iii). b) Using TPM we measured myocardial work in millimeter-size myocardial regions (millidomains). c) Negative (NW) and positive myocardial work (PW) schematically visualized in strain trajectories from millidomains, and the definition of wasted work ratio (WWR).

Fig 2. Millidomain myocardial work measurements in myocardial infarction patients (MI) and healthy controls (H). a) We observed significant group differences in positive work (PW), negative work (NW) and wasted work ratio (WWR). b) Correlations and linear regression slopes between work measurements.

Fig 3. Correlation matrix with respective Pearson correlation coefficients. *p < 0.05. PW = positive work. NW = negative work. WWR = wasted work ratio. EDV = end diastolic volume. EF= ejection fraction.


Background: Mechanical efficiency is a key modulator of cardiac performance (1-3). To quantify mechanical efficiency, non-invasive estimation of negative and positive myocardial work has emerged as a powerful method (4). However, these measurements are traditionally conducted in AHA-sectors (5), therefore reflecting efficiency between large segments, and can potentially overlook underlying changes in the myocardium. We hypothesize that mechanical efficiency, captured at the millimeter level, could reveal subtle mechanical changes that may markedly influence overall cardiac performance. Thus, we employed high-resolution motion encoded cardiovascular magnetic resonance imaging (CMR) to measure negative and positive myocardial work in millimeter-sized myocardial regions (millidomains) in myocardial infarction (MI) patients and healthy controls.

Methods: CMR was performed on 1.5T Philips Ingenia system. We recruited 20 MI patients 6 months after ST-elevation myocardial infarction and 20 age- and sex-matched healthy controls. Cine, Late Gadolinium Enhancement (LGE), and motion encoded Tissue Phase Mapping (TPM) were performed (Fig 1a). TPM parameters were: slices: 6; slice thickness: 10mm; in-plane resolution: 1.94mm2; TE: 4.1ms; TR: 15.8-16.2ms; frame rate: 50/heart cycle; flip angle 10°; venc: 20 cm/s. Blood pressure was measured immediately after CMR. Using TPM, we calculated myocardial work in up to 432 myocardial regions per heart, each covering approximately a 2.5mm² transmural area (Fig 1b). For each region, we derived work from strain measurements and wall stress estimation using the Laplace equation. Intraventricular pressure was derived non-invasively using a validated method (6). In millidomains, negative work (NW) was defined from elongation between aortic valve opening and closure, while positive work (PW) was defined from shortening in this period. The ratio of overall NW to the sum of NW and PW was defined as the wasted work ratio (WWR, Fig 1c). Left ventricular structure and function was derived from cine and LGE, and blood biomarkers were analyzed.

Results: Both PW, NW and WWR were significantly different in the MI population compared to healthy controls (Fig 2a). NW and WWR strongly correlated (r=-0.85 p< 0.001), while PW correlated to neither (NW: r=-0.07 p=0.68, WWR: r=-0.16 p=0.34), see Fig 2b. NW and WWR significantly correlated to established parameters of cardiac dysfunction and damage. This includes ejection fraction (NW: r=-0.79 p< 0.001, WWR: r=-0.78 p< 0.001); global strain (NW: r=-0.79 p< 0.001, WWR: r=-0.83 p< 0.001); and infarct size (NW: r=-0.72 p< 0.001, WWR: r=0.76 p< 0.001), see Fig. 3. 

Conclusion: We show that mechanical efficiency in myocardial millidomains decreases after MI and is associated to overall cardiac dysfunction and damage. In millidomains, this is driven by negative work, which is not counterbalanced by positive. Measurements of underlying mechanics may have the potential to deliver new insight into myocardial performance in post-ischemic remodeling.

Fig 1. Millidomain myocardial work. a) We performed cine (i), late gadolinium enhancement (ii), and advanced motion encoding tissue phase mapping (TPM (iii). b) Using TPM we measured myocardial work in millimeter-size myocardial regions (millidomains). c) Negative (NW) and positive myocardial work (PW) schematically visualized in strain trajectories from millidomains, and the definition of wasted work ratio (WWR).

Fig 2. Millidomain myocardial work measurements in myocardial infarction patients (MI) and healthy controls (H). a) We observed significant group differences in positive work (PW), negative work (NW) and wasted work ratio (WWR). b) Correlations and linear regression slopes between work measurements.

Fig 3. Correlation matrix with respective Pearson correlation coefficients. *p < 0.05. PW = positive work. NW = negative work. WWR = wasted work ratio. EDV = end diastolic volume. EF= ejection fraction.