# The Role of Mechanical Economy and Efficiency as Key Drivers of Cardiac Rehabilitation Exercise Performance Improvement in a Patient With Heart Failure and an Implanted CRT‐D: A Case Report and Literature Review

## TL;DR

A heart failure patient showed significant improvements in mechanical efficiency during cardiac rehab, beyond what traditional measures like oxygen consumption suggest.

## Contribution

This case report highlights the importance of measuring mechanical economy and efficiency in assessing cardiac rehabilitation outcomes in heart failure patients.

## Key findings

- Peak workload improved by 61% while peak oxygen consumption increased only by 9%.
- Mechanical economy and efficiency improved significantly at all physiological thresholds.
- Improvements in mechanical efficiency reveal greater external work for metabolic cost in heart failure patients.

## Abstract

Heart failure with reduced ejection fraction leads to exercise intolerance due to central and peripheral dysfunction. Improvements in exercise performance are not fully captured by traditional measures like peak oxygen consumption alone. A 57‐year‐old male with a complex cardiac medical history of hypertrophic cardiomyopathy with left ventricle non‐compaction, Wolff‐Parkinson‐White syndrome, transient ischemic stroke, and heart failure with reduced ejection fraction with an implanted cardiac resynchronization therapy defibrillator underwent cardiac rehabilitation. Cardiopulmonary exercise testing revealed a non‐proportional improvement in peak oxygen consumption (0.3 METs, 9%) versus peak workload (48 W, 61%). Gross mechanical economy and efficiency improved at all physiological thresholds: at ventilatory threshold by 11%, at respiratory compensation point by 60% and 41%, and at peak oxygen consumption by 47% and 33%, respectively. Mechanical economy and mechanical efficiency should be measured and reported for assessing rehabilitation outcomes in heart failure with reduced ejection fraction.

Conceptual framework linking Mechanical Economy (MEC) and Mechanical Efficiency (MEF) to clinical phenotypes and training response in a 57‐year‐old male patient with HFrEF and a CRT‐D. After exercise‐based cardiac rehabilitation peak workload increased disproportionately to modest changes in peak oxygen consuption. MEC/MEF improved at physiological thresholds and peak effort. MEC and MEF reveal disproportionate gains in external work for metabolic cost and should be reported alongside traditional cardiopulmonary outcomes in cardiac rehabilitation.