The Charter ( Medical Professionalism in the New Millennium.A Physician's Charter) did not deal with just the important relationship of ...
Wednesday, February 22, 2017
Cardiac remodeling -some old and new theory and some data
Following the 1975 echocardiographic study by Morganroth (1) of endurance athletes and resistance exercise athletes and several cross sectional studies that seemed to validate his work the "Morganroth Hypothesis" became the standard exercise physiology party line.
The story goes like this:
Endurance exercise brings about a volume overload or a preload stimulus to the ventricle that lead to eccentric hypertrophy which is an increase in ventricular cavity size and only slight increase in wall thickness. Resistance exercise brings about a pressure overload or an afterload stimulus which leads to concentric hypertrophy in which there is little change in cavity size but thickening of the ventricular wall.,The 2 types can be defined by the relative wall thickness (RWT) which is 2 x the posterior wall thickness divided by left ventricular diastolic diameter with a value greater than 0.42 indicating concentric hypertrophy.
Skeptics have argued that echo studies have inherent methodological error ranges too great to separate groups whose absolute values are not that far apart and MR is a much more precise method and that cross-sectional studies have limited ability to sort out group differences that are due to training from other causes of individual differences. So, what did a longitudinal study with MR imaging show.
A 2011 MRI longitudinal study, Spence et al (2) provided interesting data from which one might conclude that endurance exercise does bring about eccentric hypertrophy but resistance exercise does not increase wall thickness-at least not in the small group of resistance exercisers who worked out three times a week for six months reported in this publication .Of course, it is possible that the resistance group had not been studied long enough.
It is certainly possible that the six months training program in Spence's study was not enough to bring about concentric hypertrophy. A more recent meta analysis supplies data and analysis that indicate that there is a typical pattern for endurance exercisers and a pattern for resistance exercise more or less consistent with Morganroth's hypothesis and a in- between pattern for those who engage in activity in which there is both significant amount of volume and pressure overload such as rowing and cycling.
Plium et al (3)analyzed echocardiographic data on 1451 athletes gathered up from some 59 studies.All subjects were under the age of forty, older athletes excluded so as to not muddy up the data with the effects of aging on heart function and structure.
Basically the data conformed with Morganroth's hypothesis. Quoting the author's conclusions;
"Divergent cardiac adaptations do occur in the athletes performing dynamic and static sports..However,the classification as an endurance trained heart or a strength-trained heart is not an absolute and dichotomous concept but rather a relative concept."
So a stereotypical runner will have a different pattern from a wrestler or body builder but ventricular volume changes and wall thickening occur in both to varying degrees with the runner tending to a eccentric hypertrophy-remodeling pattern and the wrestler to a concentric pattern while athletes such as cyclists and rowers demonstrate the most marked changes both in ventricular volume and wall thickness.
More surprisingly and maybe more importantly is the observation that a sedentary life style may evoke a remodeling pattern characterized by concentric changes, i.e. no increase in ventricular volumes and a tendency to develop diastolic dysfunction.
This is what was reported by Brinker et al (4) from Southwestern Medical School in Dallas in their study of cardiac function and structure in 2900 subjects from the Cooper Center Longitudinal Study.The subjects age ranged from 42 to 67 years of age and all were either self referred or physician referred to the clinic and had a normal stress test.Based on the exercise levels achieved on the stress test four fitness levels were designated. They found that the lowest fit subjects ( presumably those with a sedentary lifestyle) had a higher prevalence of concentric remodeling as well as diastolic dysfunction than the fitter subjects. There was a 40% prevalence of concentric hypertrophy and 9 % prevalence of diastolic dysfunction ( defined as an E/A ratio greater than 1) in the lowest fit group versus less than 20 % concentric change and 2% diastolic dysfunction in the most fit group. So it is not an all on none thing and fitness does not seem to immunize against concentric hypertrophy and diastolic dysfunction but made both less likely.
Both resistance and endurance training cause cardiac remodeling but there may also be a "inactivity remodeling", as might occur in a sedentary lifestyle The ventricles remodel whether you exercise or have a sedentary lifestyle and Brinker's group suggest that the inactivity remodeling may be a precursor to diastolic heart failure (aka HFpEF) and further suggest that long term exercise might be preventive.
That is a thesis I would like to believe. I would be more convinced if it were not for the fact that while 66% of the low fit group were hypertensive so were only 38% of the fittest group were hypertensive. You wonder if that might not play a role in the concentric hypertrophy. I discussed other work by the Dallas group (see here) which, IMO, provides better evidence for the idea that long term aerobic exercise can reduce the risk of diastolic heart failure.
1. Morganroth, J et al. Comparative left ventricular dimensions in trained athletes.Annl Int Med. 1975,82(4), 521-524
2. Spence,A et al .A prospective randomized longitudinal MRI study of left ventricular adaptation to endurance and resistance exercise J of Physiology 14 nov 2011
3.Pluim,B The Athlete's Heart. A Meta-analysis of cardiac structure and function. Circulation 1999:100: 336
4.Brinker, SK et al. Association of Cardiorespiratory Fitness with Left Ventricular Remodeling and diastolic dysfunction. JACC Heart Failure.Vol 2, no.3, 2014, p238
"Humans are pattern-seeking, story-telling animals and we are quite adept at telling stories about patterns,whether they exist or not" Michael Shermer.