Clinical Profile and Outcome of Idiopathic Restrictive Cardiomyopathy
To the Editor:
We read the article by Ammash et al1 with great interest. The authors retrospectively identified 94 patients with idiopathic restrictive cardiomyopathy on the basis of a triad of echocardiographic features, including biatrial enlargement, nondilated ventricles, and normal ventricular wall thickness, in the absence of conditions known to cause pericardial disease or restrictive cardiomyopathy. The validity of this definition, however, is debatable when 74% of the patients in the cohort were in atrial fibrillation. Although atrial fibrillation is often the consequence of atrial dilatation, not as well known is the fact that atrial fibrillation may itself induce the enlargement of both atria. Sanfilippo et al2 performed serial echocardiography a mean of 20.6 months apart in a group of patients with atrial fibrillation and no underlying structural or functional cardiac abnormality. They found a significant increase in all parameters of left and right atrial size, including diameters and assessments of atrial volume. Of interest, atrial enlargement occurred in the absence of any ventricular dilatation.
Structural remodeling of the atria encompasses not only abnormality in size and function, but also histological changes, including dedifferentiation and degeneration of cardiomyocytes with replacement fibrosis.3
In the article by Ammash et al,1 only a minority of patients had cardiac catheterization and, even in these patients, restrictive hemodynamics were demonstrated in only 42%. Atrial fibrillation is a common arrhythmia that is found in 1% of persons older than 60 years and in >5% of patients >69 years old.4 Moreover, atrial fibrillation is not a benign arrhythmia; it is associated with substantial morbidity and mortality.5 Given these facts, one wonders what proportion of patients in the study by Ammash et al1 actually had primary atrial fibrillation and not restrictive cardiomyopathy.
- Copyright © 2001 by American Heart Association
Ammash NM, Seward JB, Baily KR, et al. Clinical profile and outcome of idiopathic restrictive cardiomyopathy. Circulation. 2000;101:2490–2496.
Sanfilippo AJ, Abascal VM, Sheehan M, et al. Atrial enlargement as a consequence of atrial fibrillation: a prospective echocardiographic study. Circulation. 1991;82:792–797.
Benjamin EJ, Wolf PA, D’Agostino RB, et al. Impact of atrial fibrillation on the risk of death: the Framingham Heart Study. Circulation. 1998;98:946–952.
Restrictive cardiomyopathy, as defined by the World Health Organization, is a disorder of diastolic function characterized by restrictive filling with normal ventricular size and wall thickness. It is the reduced compliance (restrictive filling) of the ventricle that results in the elevation of filling pressures, which in turn leads to atrial enlargement and not the other way around. In our study group, 74% of the patients with idiopathic restrictive cardiomyopathy, a primary disease of the myocardium (not to be confused with secondary restrictive hemodynamics seen in ischemic, hypertensive, or infiltrative myocardial diseases), were indeed in atrial fibrillation, which we believe was secondary to atrial enlargement. Although it is true that <50% of the patients in the study group had hemodynamic cardiac catheterization and/or myocardial biopsies, which is an inherent limitation of this retrospective study, all right ventricular myocardial biopsies obtained showed findings consistent with a primary myopathic process. including interstitial fibrosis and myocyte hypertrophy in the absence of any recognizable underlying heart disease. The low filling pressures noted on some of the patients during the hemodynamic study were attributed to intensive diuresis before cardiac catheterization. We should also keep in mind that a comprehensive echocardiographic examination with Doppler was extensively validated with cardiac catheterization hemodynamics. In our study, Doppler interrogation of the mitral valve inflow, when obtainable, did demonstrate a relatively shortened deceleration time, even in the presence of atrial fibrillation (deceleration time was <150 ms in 65% of the patients). Furthermore, overall prognosis did not differ between patients in sinus rhythm and those in atrial fibrillation. Therefore, although we concur with Drs Schutte and Essop that atrial fibrillation can cause atrial enlargement and is associated with increased morbidity and mortality, we think that in our study group, it was the underlying restrictive cardiomyopathy (idiopathic) that resulted in marked atrial enlargement, which in turn led to atrial fibrillation.