Properties of Myocardium in Cardiomegaly

Abstract

The adult rat's ventricular myocardium is able to increase its mass markedly while maintaining its unit quality. It does so by maintaining constant the design of the sarcomeres: an increase in length is accomplished by the addition of sarcomeres in series; an increase in tension production is accomplished by the addition of more cross-sectional area of a uniform quality. This was shown by the almost constant concentration of the contractile protein, actomyosin, as well as by the histologic evidence of the constancy in the sarcomere lengths. Functional support was obtained by the finding of an identity in the parameters of the length-tension curves; the curves differed only in the absolute magnitude of the tensions, a difference that completely disappeared when suitable corrections were made for the size of the muscle. The electrical parameters also indicated a lack of change in the quality of the excitatory membrane phenomena. However, some data were presented that suggest that the myocardium may show altered properties dependent on the age of the animal. No evidence was found in support of the concept of detrimental consequences at least with this degree of cardiomegaly. It is rather concluded that this degree of cardiomegaly is accomplished without change in the basic architecture, properties, or concentration of the contractile mechanism.

The effect of physical training upon the mechanical and metabolic performance of the rat heart

“…Ventricular volumes were not determined, and therefore, these variables cannot be accurately quantitated. However, it has been reported that passive length-tension curves of myocardium from rats that had been chronically swum are normal (4,24). This suggests that at the same atrial pressure the diastolic volume of CH and SH would be the same.…”

Normal Contractile State of Hypertrophied Myocardium after Pulmonary Artery Constriction in the Cat

“…Although earlier studies reported that contractile function of hypertrophied myocardium was normal or even "supernormal" (1)(2)(3)(4), the methods used to assess contractile state and the manner in which this function was corrected for differences in muscle mass have been criticized. More recently, Spann, Received for publication 10 May 1974 and in revised form 16 August 1974.…”

Left ventricular function in patients with chronic obstructive pulmonary disease

“…Evidence to support this impression has been gained primarily from the observation that patients dying with COPD often have left ventricular hypertrophy at postmortem examination (2)(3)(4)(5)(6)(7), and the possible mechanisms for this have been summarized (7). However, the presence of myocardial hypertrophy does not necessarily indicate depressed myocardial function since it has been demonstrated that the hypertrophied myocardium can function normally (8) or even supernormally (9)(10)(11)(12)(13). Furthermore, definitive conclusions concerning left ventricular function in these patients cannot be made from the vast amount of hemodynamic data accumulated from cardiac catheterization studied which have been summarized recently (14).…”