Post
by John Rudoff, M. D. » September 24th, 2007, 12:25 pm
It is correct that chronic athletic training will 'enlarge' the heart. However:
First, enlargement ('hypertrophy') refers either to the cavity or chamber-dimension of the ventricle; or, to the thickness of the walls. (These 2 processes have unfortunately been named 'eccentric' or 'concentric' hypertrophy in the cardiac literature, which is a bit confusing.)
Second, it is generally (though NOT completely) considered that resistance training causes muscle thickening and that distance or aerobic training causes chamber enlargement. This used to be considered an article of certainty amongst cardiologists, but this is no longer considered to be completely accurate.
Third, the original reason that this has been considered interesting is that there is a quite uncommon congenital abnormality called 'HCM', 'hypertrophic cardiomyopathy' (formerly called 'IHSS'), which causes thickening of some or all of the heart muscle. The distinctive feature of this abnormality, though, is actual disarray of the cardiac fibers, usually only discernible on autopsy or biopsy, and this condition is the leading cause of sudden cardiac death (SCD) among young (under 35) athletes. The reason that this has been interesting is that there are some general similarities in the size and shape of the heart muscle (the 'gross morphology') in the athletics-related hypertrophy and the congenital abnormality. However, only the latter, the congenital form, carries the marker of risk for SCD. Athletic hypertrophy tends to regress pretty rapidly--under 6--10 weeks--after stopping hard training.
Fourth, the work of a cardiologist named P. Spirito in Italy (who by the way trained at NIH) very interestingly demonstrated that of the entire Italian Olympic team, very, very few had significant thickening of the wall between the 2 sides of the heart; but of those, most were rowers or paddlers. The exact mechanism of this is as yet uncertain. This is probably a function of the unusual combination of both resistance and aerobic training to which we subject ourselves.
This is not, repeat and underscore is not, associated with an increased risk of SCD.
Last, echocardiography is the best way non-invasively to measure the size and thickness of the cardiac chambers; but it is technician-dependent; there can frequently be minor variations of measurement according to the exact angle of the ultrasound beam...
John Rudoff, M. D., FACC
Practice of Adult Cardiology
Portland, Oregon