Background

Myocardial work (MW) indices are novel echocardiographic parameters quantifying myocardial deformation accounting for concomitant left ventricular (LV) pressure[1]. However, their use in out-of-hospital cardiac arrest (OHCA) patients undergoing target temperature management (TTM) is still limited.

Aim

To assess MW indices in OHCA patients, serial echocardiography was performed upon ICU arrival, at TTM completion, and 24 hours after rewarming.

Methods

This substudy of the Xe-Hypotheca trial included adult OHCA survivors with ventricular fibrillation or pulseless ventricular tachycardia, randomized 1:1 to TTM at 33°C for 24 hours (n=55, control) or xenon inhalation plus TTM (n=55)[2]. Echocardiography was performed upon arrival at the intensive care unit (ICU), at the completion of TTM, and 24 hours after rewarming to assess MW indices. MW index (MWI), constructive MW (MCW), MW efficiency (MWE) and myocardial wasted work (MWW) were measured. The primary endpoint was LV ejection fraction (EF) ≥45% at 24 hours post-rewarming, indicating favourable long-term cardiac outcomes[3].

Results

Thirty-six patients (mean age 58 ± 11 years, 70% male, 39% with ST-elevation myocardial infarction, average return of spontaneous circulation time 24 ± 6 min, including 17 from the xenon group) were analyzed. MWI and MCW increased from TTM completion to 24 hours post-rewarming but showed no significant change between ICU arrival and TTM completion (Table 1). EF and global longitudinal strain (GLS) improved from ICU arrival to 24 hours post-rewarming, while no significant changes occurred between ICU arrival and TTM completion. MWI, MWE, and MCW positively correlated with EF at all time points (ICU arrival: r=0.67, r=0.81, r=0.69, all P<0.001; TTM completion: r=0.59, P=0.002; r=0.45, P=0.02; r=0.59, P=0.002; post-rewarming: r=0.64, r=0.86, r=0.64, all P<0.001). Conversely, MWW correlated inversely with EF upon ICU arrival (r=-0.56, P=0.003) and 24 hours post-rewarming (r=-0.72, P<0.001). Central venous pressure (CVP) was inversely correlated with MWI and MCW upon ICU arrival (r=-0.49, P=0.02; r=-0.50, P=0.01) and 24 hours post-rewarming (r=-0.61, P=0.002; r=-0.53, P=0.008). Higher MCW on ICU arrival and TTM completion independently predicted EF≥45% at 24 hours post-rewarming (ICU arrival: OR=1.0041, 95% CI: 1.0005–1.0077, P=0.026; TTM completion: OR=1.005, 95% CI: 1.0008–1.0092, P=0.02). MCW cut-offs predicting EF ≥45% were ≥1090 mmHg% on ICU arrival (79% sensitivity, 82% specificity, AUC=0.805) and ≥902 mmHg% at TTM completion (100% sensitivity, 64% specificity, AUC=0.825, Figure 1).

Conclusion

Constructive myocardial work on ICU arrival and at the completion of TTM predict preserved LV systolic function 24 hours after rewarming post-OHCA. On ICU arrival, constructive work is inversely related to central venous pressure. Myocardial work indices may provide useful information about hemodynamic conditions and short-term LV function in OHCA patients.