Focus Topic: Myocardial Work in Health and Disease
Clinical Investigation
Noninvasive Myocardial Work Index: Characterizing the Normal and Ischemic Response to Exercise

https://doi.org/10.1016/j.echo.2020.05.003Get rights and content

Highlights

  • During normal exercise myocardial work increases and work efficiency is preserved.

  • In exercise-induced ischemia, work decreases in affected segments.

  • In exercise-induced ischemia, work fails to increase globally.

  • In exercise-induced ischemia efficiency decreases due to reduced constructive work.

  • Myocardial work can be used to identify inducible ischemia.

Background

Myocardial work index (MWI) and work efficiency are new parameters for assessing left ventricular function. We aim to characterize the normal response to exercise in a mixed population and determine whether MWI can identify patients with inducible ischemia.

Methods

Patients were retrospectively enrolled from an existing database of exercise stress echocardiography. Inclusion criteria were a clinical indication of possible ischemia and technical suitability to calculate MWI. Exclusion criteria were abnormal baseline left ventricular function or inadequate image quality. Echocardiograms positive for ischemia were defined by independent visual assessment and compared with angiographic findings where available. Myocardial work index was determined using a proprietary algorithm and efficiency calculated as constructive work divided by the sum of constructive and wasted work.

Results

A total of 177 patients met inclusion criteria; 117 were excluded, leaving 40 normal and 20 positive tests. During normal exercise, global MWI increased 54% (from 2,296 to 3,523 mm Hg%) and efficiency remained at 96%. However, in patients with inducible ischemia, MWI decreased in affected segments, global MWI did not increase (2,069-2,070 mm Hg%), and global efficiency fell from 93% to 87%. The receiver operating characteristic curve for MWI had an area under the curve of 0.94.

Conclusions

During normal exercise, MWI increases and efficiency remains unchanged. However, during exercise-induced ischemia, MWI paradoxically decreases in affected segments, while globally MWI fails to increase and efficiency decreases. We have demonstrated that MWI can be applied to stress echocardiography to identify ischemia, but its utility remains uncertain. Further research that makes comparisons with an objective measure of functional ischemia is needed.

Section snippets

Methods

Patients were retrospectively enrolled from an existing database of exercise stress echocardiography across three regional institutions. Inclusion criteria were a clinical indication of possible ischemia and technical suitability to calculate myocardial work. Technical suitability included the absence of atrial fibrillation, aortic stenosis, or other significant valve disease or valve replacement, the availability of apical four-chamber, three-chamber, and two-chamber views, sufficient frame

Results

The database from 2015-19 identified 312 echocardiograms; 177 were included for further analysis. Criteria excluded 117 (51 high-risk subclinical cardiomyopathy, 43 abnormal baseline function, 22 inadequate image quality, 1 known cardiomyopathy). A total of 40 normal studies and 20 positive studies were identified for further analysis. Clinical characteristics are detailed in Table 1. No patients with normal stress echocardiography proceeded to an angiogram or had a new diagnosis of ischemia or

Discussion

This study characterizes the myocardial work and work efficiency response to exercise in patients with and without inducible ischemia. In normal conditions, myocardial work increases during exercise and efficiency remains unchanged. However, during exercise-induced ischemia, MWI paradoxically decreases in affected segments, while globally MWI fails to increase and efficiency decreases.

Our result of a 54% increase in myocardial work during exercise is consistent with previous invasive (48%

Conclusion

During normal exercise, myocardial work increases and efficiency remains unchanged. However, during exercise-induced ischemia, MWI paradoxically decreases in affected segments, while globally MWI fails to increase and efficiency decreases. Myocardial work is objective, quantitative, and load independent, and we demonstrate the feasibility of applying it to stress echocardiography to identify ischemia, but its utility remains uncertain. Further research with a larger prospective study making

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  • Cited by (20)

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      Edwards et al. reported MW indices were more sensitive to detect significant CAD (>70% stenosis) in patients with no visually regional wall motion abnormalities and preserved LVEF.29 In a study of exercise stress responses, Borrie et al. demonstrate the difference in MW indices between patients with and without inducible ischemia.30 During exercise stress, for patients with inducible ischemia, regional myocardial work index paradoxically decreased in affected segments, GWI had no obvious change, and GWE was significantly reduced, whereas GWI increased by 54% and efficiency was preserved in healthy controls.

    • Global Myocardial Work Combined with Treadmill Exercise Stress to Detect Significant Coronary Artery Disease

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      Particularly, peak GWE and peak GWW had a relatively high diagnostic value for significant CAD patients. In another recent study, Borrie et al.12 revealed that GWI and GWE could characterize the normal and ischemic responses to exercise. Their study finally included 40 normal subjects and 20 patients with positive stress echocardiography results, and the sample size was smaller than that of our study.

    • The Utility of Myocardial Work in Clinical Practice

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      Several studies have been performed on MW and stress echocardiography. Borrie et al.27 investigated the normal response to exercise and sought to identify patients with inducible ischemia with MW. The group determined that during normal exercise, GWI increases and GWE is unchanged.

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    Conflicts of Interest: None.

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