When Myocardial Work Meets Exercise: Redefining Functional Reserve in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) remains a paradox of modern cardiology: a disease defined by structural excess yet functionally characterized by insufficiency. Patients may exhibit marked myocardial hypertrophy while maintaining a normal ejection fraction and minimal symptoms at rest, only to reveal profound exercise limitation and arrhythmic vulnerability under stress [1, 2]. This dissociation between structure and apparent resting function has long challenged clinicians seeking sensitive markers of disease severity and progression. In this context, the study by Lin et al. [3] introduces a timely and conceptually important approach: the integrated assessment of left-ventricular myocardial work and cardiopulmonary exercise performance.Their findings reinforce a critical shift in cardiovascular imaging – from static evaluation of myocardial deformation toward dynamic characterization of energetic efficiency and contractile reserve. By combining non-invasive pressure-strain loop (PSL)-derived myocardial work with cardiopulmonary exercise testing (CPET), the authors illuminate a fundamental pathophysiological signature of HCM: the inability of hypertrophied myocardium to augment constructive work under physiological stress, accompanied by disproportionate increases in wasted work and mechanical dispersion [3, 4].Beyond deformation: myocardial work as a functional currency: Over the past decade, global longitudinal strain has emerged as a sensitive marker of systolic dysfunction in HCM, often abnormal despite preserved ejection fraction. Yet global longitudinal strain remains load-dependent and provides limited insight into myocardial energetics. Myocardial work analysis, derived from PSLs integrating strain and blood pressure, offers a more physiologically grounded metric by approximating the mechanical energy generated during systole [5, 6].Lin et al. [3] demonstrate that patients with non-obstructive HCM exhibit markedly reduced global constructive work and work efficiency alongside increased wasted work at rest, despite normal chamber size and ejection fraction. These findings underscore that contractile impairment in HCM is not merely a reduction in deformation amplitude but a deterioration in the efficiency with which myocardial fibers convert metabolic energy into effective stroke work. This distinction is crucial. In hypertrophied myocardium, fiber disarray and interstitial fibrosis create heterogeneous activation patterns and local energy dissipation. Myocardial work, therefore, becomes a more direct reflection of disease biology than strain alone, capturing both contractile strength and synchrony [4]. In this sense, myocardial work may be viewed as the “functional currency” of the ventricle – quantifying how much useful mechanical output is produced per cardiac cycle.Stress unmasks the energetic deficit of hypertrophy: The most compelling contribution of the present study lies not in resting abnormalities but in their dynamic evolution during exercise. In healthy individuals, exercise provokes a coordinated increase in constructive work and global work index, reflecting enhanced contractility and efficient recruitment of myocardial reserve. Lin et al. show that this physiological adaptation is strikingly absent in HCM: constructive work fails to increase, while wasted work and strain dispersion rise significantly after CPET [7, 8].This pattern reveals a defining characteristic of hypertrophic myocardium – energetic rigidity. Faced with increased afterload and metabolic demand, the diseased ventricle cannot augment useful work; instead, it dissipates energy through asynchronous contraction and ineffective fiber shortening. The result is an apparent plateau in global work despite escalating oxygen demand, a mechanical correlate of the well-known exercise intolerance of HCM. Conceptually, this observation reframes HCM as a disorder of impaired contractile reserve rather than solely excessive hypertrophy. It also aligns with emerging evidence from metabolic imaging and microvascular studies demonstrating reduced energetic efficiency and limited ATP availability in hypertrophied myocardium. The inability to increase constructive work during stress thus integrates structural, metabolic, and mechanical derangements into a unified functional phenotype. A second key insight arises from the relationship between myocardial work parameters and maximal wall thickness. The authors identify peak strain dispersion, constructive work, and wasted work as independent correlates of hypertrophy severity [2, 3]. These finding positions myocardial work metrics as intermediaries between structural remodeling and clinical expression. Notably, associations between maximal wall thickness and CPET indices observed in univariable analysis disappeared after adjustment, suggesting that exercise capacity in HCM is mediated primarily through mechanical inefficiency rather than hypertrophy per se. In other words, wall thickness influences symptoms not directly but through its impact on synchrony and energetic performance. This distinction has practical implications: therapies aimed at improving myocardial efficiency or coordination may enhance functional status even without substantial regression of hypertrophy. The integrated PSL-CPET approach thus provides a mechanistic bridge linking imaging and physiology. Exercise intolerance in HCM emerges not simply from diastolic stiffness or outflow obstruction but from an inability to convert metabolic demand into effective systolic work. Such insights advance our understanding beyond descriptive correlations toward causal pathways [4].Traditional HCM assessment relies largely on static parameters – wall thickness, obstruction gradients, fibrosis burden, and resting strain. While prognostically relevant, these markers capture only snapshots of myocardial state. The present study advocates a dynamic phenotype, defined by how the ventricle responds to physiological challenge (Fig. 1).Three elements characterize this phenotype.1.Blunted augmentation of constructive work during stress2.Exaggerated increase in wasted work and mechanical dispersion3.Mismatch between metabolic demand and mechanical outputTogether, these features describe a ventricle that is structurally hypertrophied yet functionally constrained – a myocardium capable of contraction but incapable of coordinated, energy-efficient recruitment under load. Such a framework resonates with contemporary concepts of myocardial reserve across cardiomyopathies and may refine risk stratification in HCM [7, 9, 10].Importantly, this dynamic perspective parallels shifts occurring in other domains of cardiology. In heart failure with preserved ejection fraction, stress echocardiography has revealed impaired contractile reserve despite normal resting metrics. In valvular disease, exercise testing unmasks latent dysfunction. Extending this paradigm to HCM via myocardial work analysis represents a logical and innovative progression [3].Beyond pathophysiology, the combined PSL-CPET approach may carry several clinical implications:Early detection of subclinical dysfunction: the observation that myocardial work abnormalities precede changes in ejection fraction or chamber size suggests potential utility in identifying patients at risk of functional decline. Such sensitivity is particularly relevant in genotype-positive or mildly hypertrophied individuals.Objective quantification of exercise limitation: by linking myocardial work response directly to CPET performance, clinicians may better distinguish cardiac from peripheral determinants of reduced peak oxygen consumption. This could refine exercise recommendations and rehabilitation strategies.Monitoring therapeutic interventions: emerging treatments in HCM – including myosin inhibitors – aim to improve energetic efficiency and contractile balance. Myocardial work reserve during stress may provide a mechanistic endpoint to evaluate such therapies, complementing traditional imaging and symptomatic measures.Risk stratification: mechanical dispersion and wasted work have been associated with arrhythmic risk in other cardiomyopathies. Their augmentation during stress could potentially identify electrically unstable substrates in HCM, although prospective validation is required.Thus, myocardial work under stress may evolve from a descriptive imaging parameter into a functional biomarker guiding management [3].While conceptually compelling, several methodological aspects warrant discussion. The study cohort is modest and limited to non-obstructive HCM, precluding phenotype-specific analysis. Exercise protocols and post-exercise imaging timing may influence measured responses, and load-independent confirmation using invasive pressure–volume loops remains desirable. Longitudinal outcome data are also lacking, leaving prognostic implications speculative (Fig. 1).Nevertheless, these limitations do not diminish the central message: myocardial work dynamics during physiological stress reveal a fundamental defect in hypertrophic myocardium. Larger multicenter studies integrating myocardial work, metabolic imaging, and outcomes are now needed to define normative stress responses and clinical thresholds [1, 7, 9].Future investigations might explore: Differences in work reserve between obstructive and non-obstructive phenotypesInteraction between myocardial fibrosis extent and stress-induced wasted workEffects of pharmacologic therapy on myocardial work augmentationPrognostic value of post-exercise mechanical dispersionSuch work could ultimately establish myocardial work reserve as a cornerstone of HCM evaluation. The broader significance of this study lies in its conceptual reframing of ventricular performance. For decades, ejection fraction dominated assessment of systolic function, later complemented by strain imaging. Myocardial work analysis now extends this trajectory by incorporating load and energetics, offering a more physiologically complete measure of contractility.In HCM, where hypertrophy masks dysfunction, such refinement is particularly valuable. The ventricle’s failure to augment constructive work during stress – despite preserved ejection fraction – captures the essence of the disease: mechanical activity without efficient performance. This distinction parallels the clinical observation of patients who appear stable at rest yet deteriorate under exertion.By integrating myocardial mechanics with exercise physiology, Lin et al. move us closer to a unified model of HCM in which structure, metabolism, and function converge. Their work underscores that the hypertrophic ventricle is not merely thickened but energetically compromised and mechanically discordant [3].The combination of PSL-derived myocardial work and CPET offers a powerful lens through which to view HCM. It reveals a ventricle unable to translate increased demand into effective mechanical output – an energetic bottleneck at the heart of exercise intolerance.As cardiovascular imaging evolves toward dynamic and mechanistic assessment, myocardial work reserve may emerge as a defining marker of disease severity and therapeutic response in HCM. The study by Lin et al. thus represents more than a technical advance; it signals a shift from measuring how the hypertrophic heart looks to understanding how it performs. In doing so, it reminds us that true ventricular function is not the magnitude of contraction at rest, but the capacity to generate coordinated, efficient work when the organism demands it most.E.D. received a grant and fees from GE healthcare and Abbott. No conflicts of interest were declared for P.C. and A.A.W.This study was not supported by any sponsor or funder.E.D. contributed to writing. P.C. did the figure and reviewed the whole manuscript. A.A.W. reviewed everything.