The respiratory exchanges of the heart in the diabetic animal

XXII.—The Metabolism of the Frog's Isolated Heart

Theories regarding the chemistry of the contraction process in striped muscle have been revolutionised during the last year. The Hill-Meyerhof theory was based on the assumption that the contraction process was due to the liberation of lactic acid by the break-down of glycogen, a non-oxidative reaction, and that the recovery process consisted in the oxidation of part of the lactic acid and the resynthesis of glycogen from the remainder. Meyerhof now believes (1, p. 305) that contraction is produced by the break-down of creatin-phosphoric acid (phosphagen), and that the energy produced by carbohydrate break-down is utilised to resynthesise phosphagen.

Early administration of trimetazidine may prevent or ameliorate diabetic cardiomyopathy

Diabetic cardiomyopathy is a type of cardiac dysfunction resulting from diabetes, independent of vascular or valvular pathology. It clinically manifests initially as asymptomatic diastolic dysfunction and then progresses to symptomatic heart failure. Two major contributors to the development of diabetic cardiomyopathy, which are unique to diabetes, are hyperglycemia and diabetes-related alterations in myocardial metabolism. Diabetes mellitus is characterized by reduced glucose and lactate metabolism and enhanced fatty acid metabolism, which are the early consequences of the disease. Studies on the effect of intensive glucose control on heart failure events in patients with diabetes have been conducted with neutral results. However, no study on the effect of metabolic modulators on the prevention of heart failure has been reported. Trimetazidine, a 3-ketoacyl coenzyme A thiolase (3-KAT) inhibitor, shifts cardiac energy metabolism from free fatty acid oxidation to glucose oxidation by inhibiting mitochondrial long-chain 3-KAT, and is used clinically as an effective antianginal agent. Studies have shown that trimetazidine improves heart function in patients with idiopathic cardiomyopathy and in diabetic patients with cardiac ischemia or heart failure. In addition to being effective, trimetazidine has only mild side effects. Therefore, instead of routine administration of trimetazidine for the treatment of diabetic cardiomyopathy, we hypothesize that the early application of trimetazidine may prevent or ameliorate diabetic cardiomyopathy. In addition to life style modifications, ACEI, ARB, and beta-blockers, which have been recommended in the past, trimetazidine should be administered to those patients with impaired glucose tolerance or patients in the early course of diabetes. In this way, we may reduce the prevalence of heart failure and improve the long-term survival of patients with diabetes through early normalization of the myocardial substrate metabolism.

Prognostic implications of relations of left ventricular systolic dysfunction with body composition and myocardial energy expenditure: the Strong Heart Study

OBJECTIVE

We sought to investigate prognostic implications of the relationships of estimated left ventricular (LV) myocardial energy expenditure (MEE) with LV systolic dysfunction, body composition, and inflammation in a population-based sample of adults without overt congestive heart failure.

METHODS

Echocardiography was used to assess LV ejection fraction (EF) and MEE. Body composition was evaluated by bioelectric impedance. Dietary recall was used to assess 24-hour calorie intake. Participants in the Strong Heart Study without prior congestive heart failure and with all needed data available (n = 3087) were divided based on LV EF (>55%, 54%-45%, or <45%).

RESULTS

Participants with EF less than 45% were older and they had lower body mass index, adipose mass, fat-free mass, and 24-hour calorie intake than participants with normal EF (>/=55%), and had greatest reductions of body mass index and physical activity in a time interval of 3.5 years, on average, elapsed between an initial clinical assessment and the evaluation at the time of the echocardiographic examination (P < .01). Lower EF was associated with male sex, hypertension, diabetes, coronary heart disease, and higher fibrinogen, C-reactive protein, and plasma creatinine levels (all P < .01). MEE was higher with lower EF (all P < .001). In Cox regression models, during approximately 8 years of observation, MEE comprised between 97 and 123 cal/min and MEE greater than 123 cal/min were associated with 2.5-fold and additional 3.3-fold higher rates of cardiac death, respectively, compared with MEE less than 97 cal/min, independently of EF, body composition, and other covariates. However, lower adipose mass predicted increased risk of cardiac death independent of MEE and EF.

CONCLUSION

In a population-based sample of adults including ambulatory individuals with depressed LV systolic function but without overt congestive heart failure, depressed EF was associated independently with higher MEE, lower adipose mass, and higher fibrinogen. However, increased MEE and lower adipose mass predicted cardiac death independently of EF and other covariates.

Associations of aortic and mitral regurgitation with body composition and myocardial energy expenditure in adults with hypertension: the Hypertension Genetic Epidemiology Network study

BACKGROUND

It has been reported that aortic regurgitation, mitral valve regurgitation, or both are associated with lower body mass index, an index of body adiposity. However, the relations of valvular regurgitation to body composition and myocardial bioenergetic expenditure have not been previously investigated in a population-based sample.

METHODS

We selected 1496 patients with hypertension who did not have diabetes mellitus to participate in the Hypertension Genetic Epidemiology Network (HyperGEN) study. We excluded participants with severe aortic or mitral stenosis or with known coronary heart disease. Bioimpedance was used to assess body composition. Echocardiography was used to assess left ventricular (LV) structure and function and to calculate myocardial workload (expressed as energy expenditure) from end-systolic stress, ejection time, and stroke volume. The study sample was divided into groups without mitral or aortic regurgitation (control subjects, n = 1175), with mild valvular regurgitation (1+, n = 246), and with at least moderate (>or=2+) mitral or aortic regurgitation (n = 75).

RESULTS

The mean patient age was higher with more severe valvular insufficiency. Sex distribution and blood pressure were similar among the 3 groups. Body mass index and fat mass were significantly lower with more severe valvular regurgitation, whereas fat-free mass was only slightly lower in the group with >or=2+ regurgitation compared with control subjects. Skinfold thicknesses (brachial and subscapular) were lower with more severe valvular regurgitation, whereas self-reported physical activity per week was similar among the 3 groups. LV mass and circumferential end-systolic stress were higher with more severe valvular regurgitation. Noninvasively estimated myocardial energy expenditure was slightly higher in participants with 1+ valvular regurgitation and was significantly higher with >or=2+ regurgitation. Ejection fraction was mildly lower with >or=2+ aortic insufficiency, mitral insufficiency, or both. Midwall shortening and stress-corrected midwall shortening did not differ among groups.

CONCLUSIONS

In a population-based sample of adults with hypertension and without diabetes mellitus, known coronary heart disease, or significant valvular stenosis, mitral and aortic regurgitation were associated with higher LV mass and total myocardial biomechanical workload but with lower body fat mass and slightly lower body fat-free mass, which suggests that global myocardial bioenergetic expenditure is elevated by concomitant valvular regurgitation beyond the effect of pressure overload caused by hypertension.

Charles Arthur Lovatt Evans, 1884-1968

Charles Lovatt Evans, Emeritus Professor of Physiology, University of London, and a former Vice-President of the Royal Society, died on 29 August 1968, at the age of 84, at his home at Winterslow, near Salisbury. He was the foremost pupil and a lifelong associate of E. H. Starling, Jodrell Professor of Physiology at University College London, and eventually occupied the same chair. Lovatt Evans was born in Birmingham and spent the whole of his childhood and early manhood there. His father Charles Evans taught music— piano and violin—and was a man of many interests, of which ancient history was one, and he started to learn Greek when in his sixties. Although a humorist he had somewhat rigid views on religion, life and death, and held the view that the more you do for people the less they do for themselves, so Lovatt Evans was largely left to himself to decide upon his future and surmount the difficulties of finding ways and means. His mother seemed to him to be of rather an aloof nature, spending much of her time in intellectual pursuits often at the expense of her domestic duties. The result was that in his home life he was lonely.

The effect of exercise on coronary blood flow, myocardial oxygen consumption and cardiac efficiency in man

It has been known that exercise causes an increase in the coronary blood flow in animals. The present work has been carried out to study the effect of exercise on coronary blood flow and myocardial oxygen consumption of the human heart in vivo. The results indicate that the heart responds to the increased load of exercise with a rise in coronary blood flow. Since the arteriovenous coronary oxygen difference shows little change, the increase in oxygen consumption of the heart muscle is primarily the result of an increased coronary blood flow. As the cardiac work rises more than the myocardial oxygen consumption, the left ventricular efficiency increases. The response of the failing heart muscle to acute increases in load produced by exercise does not differ from that of the normal heart or of the isolated heart.