CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Barry J. Maron, MD*,
Martin S. Maron, MD,
E. Douglas Wigle, OC, MD and
Eugene Braunwald, MD
* Minneapolis Heart Institute Foundation, 920 East 28th Street, Suite 620, Minneapolis, Minnesota 55407 (Email: hcm.maron{at}mhif.org).
We appreciate the correspondence from Dr. Murgo, stimulated by our recent historical review focused on the evolving understanding of left ventricular (LV) outflow gradients in hypertrophic cardiomyopathy (HCM) (1). Dr. Murgo has had an important role in this conversation, which has spanned virtually the last 5 decades (2), for this heterogeneous disease with complex ejection dynamics (1,3).
However, on the issue of whether obstruction represents true mechanical impedance we must depart sharply from ideas resolutely held by Dr. Michael Criley in the 1960s, which we believe have plagued the contemporary understanding of HCM and its management, that is, that somehow LV outflow gradients are incidental to this disease and are not responsible for heart failure symptoms that disable many patients.
We would like to take this opportunity fortuitously afforded by Dr. Murgo's letter to once again underscore a crucial principle in HCM, that is, subaortic gradients due to mitral valve systolic anterior motion represent true mechanical obstruction to LV outflow and are responsible for high intraventricular pressures and increased wall stress, which (in association with mitral regurgitation) lead to exertional dyspnea and physical limitation compromising quality of life.
Fifty years after the initial description of HCM (1), evidence for the clinical significance of true obstruction to outflow in HCM is overwhelming, having recently been demonstrated in large cohorts followed up for long periods of time (1,4,5). Relief of LV outflow obstruction by surgical septal myectomy (or selectively by alcohol ablation) has been shown repeatedly to relieve heart failure symptoms, and in the case of myectomy, to enhance long-term survival (5). Indeed, this is not unlike the clinical experience with obstruction due to aortic valve stenosis, albeit with different ejection dynamics.
The present discussion is reminiscent of the "second HCM obstruction debate" 25 years ago at the American College of Cardiology meeting (1) when Dr. Murgo lectured passionately about the nuances of LV ejection dynamics and nomenclature, but in the process may not have addressed the essential clinical message, that is, that outflow gradients (and secondary mitral regurgitation) are associated with substantially elevated LV systolic (and diastolic) pressures, which can cause disabling symptoms but are mechanically reversible by septal reduction intervention and with resultant restoration of quality of life and longevity.
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1. Maron BJ, Maron MS, Wigle ED, Braunwald E. 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 J Am Coll Cardiol 2009;54:191-200.[Abstract/Free Full Text]2. Murgo JP, Alter BR, Dorethy JF, Altobelli SA, McGranahan Jr. GM. Dynamics of left ventricular ejection in obstructive and nonobstructive hypertrophic cardiomyopathy J Clin Invest 1980;66:1369-1382.[Web of Science][Medline] 3. Maron BJ. Hypertrophic cardiomyopathy: a systematic review JAMA 2002;287:1308-1320.[Abstract/Free Full Text] 4. Maron MS, Olivotto I, Betocchi S, et al. Effect of left ventricular outflow tract obstruction on clinical outcome in hypertrophic cardiomyopathy N Engl J Med 2003;348:295-303.[CrossRef][Web of Science][Medline] 5. Ommen SR, Maron BJ, Olivotto I, et al. Long-term effects of surgical septal myectomy on survival in patients with obstructive hypertrophic cardiomyopathy J Am Coll Cardiol 2005;46:470-476.[Abstract/Free Full Text]
Related Article
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Have We Really Come to Understand the Relationship Between the Left Ventricular Outflow Tract Gradient and Left Ventricular Emptying in Hypertrophic Cardiomyopathy?
- Joseph P. Murgo
J. Am. Coll. Cardiol. 2010 55: 608.
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