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FOCUS ISSUE: HYPERTROPHIC CARDIOMYOPATHY: STATE-OF-THE-ART PAPER

The 50-Year History, Controversy, and Clinical Implications of Left Ventricular Outflow Tract Obstruction in Hypertrophic Cardiomyopathy

From Idiopathic Hypertrophic Subaortic Stenosis to Hypertrophic Cardiomyopathy

Barry J. Maron, MD^_*,_*, Martin S. Maron, MD, E. Douglas Wigle, OC, MD and Eugene Braunwald, MD

^_* Hypertrophic Cardiomyopathy Center, Minneapolis Heart Institute Foundation, Minneapolis, Minnesota
Hypertrophic Cardiomyopathy Center, Tufts Medical Center, Boston, Massachusetts
TIMI Study Group, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts
Division of Cardiology, Toronto General Hospital, Toronto, Ontario, Canada

Manuscript received April 29, 2008; revised manuscript received November 12, 2008, accepted November 12, 2008.

^_* Reprint requests and correspondence: Dr. Barry J. Maron, Hypertrophic Cardiomyopathy Center, Minneapolis Heart Institute Foundation, 920 East 28th Street, Suite 620, Minneapolis, Minnesota 55407 (Email: hcm.maron{at}mhif.org).

Dynamic obstruction to left ventricular (LV) outflow was recognized from the earliest (50 years ago) clinical descriptions of hypertrophic cardiomyopathy (HCM) and has proved to be a complex phenomenon unique in many respects, as well as arguably the most visible and well-known pathophysiologic component of this heterogeneous disease. Over the past 5 decades, the clinical significance attributable to dynamic LV outflow tract gradients in HCM has triggered a periodic and instructive debate. Nevertheless, only recently has evidence emerged from observational analyses in large patient cohorts that unequivocally supports subaortic pressure gradients (and obstruction) both as true impedance to LV outflow and independent determinants of disabling exertional symptoms and cardiovascular mortality. Furthermore, abolition of subaortic gradients by surgical myectomy (or percutaneous alcohol septal ablation) results in profound and consistent symptomatic benefit and restoration of quality of life, with myectomy providing a long-term survival similar to that observed in the general population. These findings resolve the long-festering controversy over the existence of obstruction in HCM and whether outflow gradients are clinically important elements of this complex disease. These data also underscore the important principle, particularly relevant to clinical practice, that heart failure due to LV outflow obstruction in HCM is mechanically reversible and amenable to invasive septal reduction therapy. Finally, the recent observation that the vast majority of patients with HCM have the propensity to develop outflow obstruction (either at rest or with exercise) underscores a return to the characterization of HCM in 1960 as a predominantly obstructive disease.

Key Words: cardiomyopathies • hypertrophic • cardiac surgery • heart catheterization • heart failure • heart failure treatment • hypertrophy

Abbreviations and Acronyms   HCM = hypertrophic cardiomyopathy   LV = left ventricular   SAM = systolic anterior motion

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