LETTER TO THE EDITOR
Myocardial bridging of the left anterior descending coronary artery in children with hypertrophic cardiomyopathy: Reply
Lameh Fananapazir, MD, FRCPa,
Saidi A. Mohiddin, MD, MRCPa and
Joanna Shih, PhDa
a Electrophysiology and Inherited Heart Diseases Section, Cardiology Branch, Building 10, Room 7B-15, 10 Center Drive, MSC 1650, Bethesda, MD 20892-1650, USA
fananapa{at}nih.gov
The report by Yetman et al. (1) that bridging of the left anterior descending (LAD) artery causes myocardial ischemia, arrhythmia, and sudden death in children with hypertrophic cardiomyopathy (HCM) prompted us to examine the clinical correlates of myocardial bridging in a larger population of HCM children using current techniques and risk evaluation (2).
Myocardial bridging was present in 40% of our children, and it frequently affected arteries other than the LAD. Myocardial ischemia was also common, being present in 65% of the children. Notably, however, the distribution of myocardial perfusion abnormalities, identified by exercise thallium scintigraphy, was unrelated to the presence, severity, or distribution of coronary bridging. Instead, we found that myocardial bridging was more common in children with more severe cardiac disease. Indeed, multivariate analysis suggested that the severity of the cardiac hypertrophy and the compression of septal branches were independent predictors of myocardial ischemia.
We were unable to confirm that myocardial bridging was associated with greater symptoms, prolonged myocardial repolarization, higher incidence of ventricular tachycardia (VT) during ambulatory electrocardiographic monitoring, or VT induced at electrophysiologic study, or, importantly, that it affected prognosis.
The different findings may be attributed to several limitations of the study of Yetman et al. (1): 1) children treated as early as the 1950s were included; 2) two-thirds of the children were excluded due to inadequate data; 3) bridging was diagnosed by, presumably, aortography rather than selective coronary angiography (only severe and mid-LAD bridging were detected); 4) survival was calculated from diagnosis of HCM rather than related to age (the children with bridging were older and in a more at-risk age group than were the children without bridging); and 5) compression of the septal perforators, an important determinant of myocardial perfusion in our study, was not considered. Further, given the limitations of angiography, we have reservations about the validity of measurements of early diastolic coronary artery compression.
In children, HCM is a complex disease, and myocardial ischemia is only one of several identified potential causes of sudden death in this subgroup (3). Additionally, several factors unrelated to bridging have also been implicated in myocardial ischemia (4).
Our study indicates that it is unlikely that bridging is an independent predictor of prognosis in HCM children. We therefore recommend caution in advising its surgical correction.
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References
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1. Yetman AT, McCrindle BW, MacDonald C, Freedom RM, Gow R. Myocardial bridging in children with hypertrophic cardiomyopathy—a risk factor for sudden death. N Engl J Med. 1998;339:1201–1209[Abstract/Free Full Text]
2. Mohiddin SA, Begley D, Shih J, Fananapazir L. Myocardial bridging does not predict sudden death in children with hypertrophic cardiomyopathy but is associated with more severe cardiac disease. J Am Coll Cardiol. 2000;36:2270–2278[Abstract/Free Full Text]
3. Dilsizian V, Bonow RO, Epstein SE, Fananapazir L. Myocardial ischemia detected by thallium scintigraphy is frequently related to cardiac arrest and syncope in young patients with hypertrophic cardiomyopathy. J Am Coll Cardiol. 1993;22:796–804[Abstract]
4. Cannon RO, Rosing D, Maron BJ, et al. Myocardial ischemia in patients with hypertrophic cardiomyopathy: contribution of inadequate vasodilator reserve and elevated left ventricular filling pressures. Circulation. 1985;71:234–243[Abstract/Free Full Text]
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