Cardiac performance in ventricular hypertrophy induced by pressure and volume overloading

Effect of endurance exercise training on left ventricular size and remodeling in older adults with hypertension

BACKGROUND

It is not known whether exercise training can induce a reduction of blood pressure (BP) and a regression of left ventricular hypertrophy (LVH) in older hypertensive subjects. This study was designed to determine whether endurance exercise training, by lowering BP, can induce regression of LVH and left ventricular (LV) concentric remodeling in older hypertensive adults.

METHODS

We studied 11 older adults with mild to moderate hypertension (BP 152.0 +/- 2.5/91.3 +/- 1.5 mm Hg, mean +/- SE), 65.5 +/- 1.2 years old, who exercised for 6.8 +/- 3.8 months. Seven sedentary hypertensive (BP 153 +/- 3/89 +/- 2 mm Hg) subjects, 68.5 +/- 1 years old, served as controls. LV size and geometry and function were assessed with the use of two-dimensional echocardiography.

RESULTS

Exercise training increased aerobic power by 16% (p < .001), and it decreased systolic (p < .05) and diastolic (p < .05) BP, LV wall thickness (from 12.8 +/- 0.4 mm to 11.3 +/- 0.3 mm; p < .05), and the wall thickness-to-radius (h/r) ratio (from 0.48 +/- 0.02 to 0.41 +/- 0.01; p < .05). There were no significant changes in the controls. The changes in LV mass index (deltaLVMI) were different between the two groups. LV mass index decreased in the exercise group (deltaLVMI - 14.3 +/- 3.3 g) but not in the controls (deltaLVMI 1.4 +/- 4.1 g; p = .009). A multiple stepwise regression analysis showed that among clinical and physiological variables including changes in resting systolic BP, aerobic power, body mass index, and systolic BP during submaximal and maximal exercise, only the reduction in resting systolic BP correlated significantly with a regression of concentric remodeling (delta h/r ratio r = .80; p = .003). The other variables did not add to the ability of the model to predict changes in the h/r ratio.

CONCLUSIONS

The data suggest that exercise training can reduce BP and induce partial regression of LVH and LV concentric remodeling in older adults with mild or moderate hypertension.

Reduction of left ventricular hypertrophy: how beneficial?

Left ventricular hypertrophy (LVH) can no longer be considered a compensatory adaptation of the heart serving to normalize the increased wall stress in hypertension. Recent studies have indicated that LVH is a powerful pressure-independent risk factor for cardiovascular morbidity and mortality. The pathophysiologic sequelae of LVH are reduced ventricular filling and contractility, ventricular dysrhythmias, and diminished coronary reserve or myocardial ischemia. Left ventricular hypertrophy can be reduced by antihypertensive therapy, although not all drugs are equipotent in this regard. Recent studies have shown that such a reduction also improves the pathophysiologic sequelae of LVH, that is, ventricular filling, coronary reserve, and ventricular dysrhythmias, and maintains left ventricular pump function. Although the reversal of these pathophysiologic findings is encouraging, it remains unknown whether a reduction of LVH will ultimately reduce the excessive risk of sudden death, acute myocardial infarction, and congestive heart failure that has been associated with this disorder independent of arterial pressure.

Left ventricular hypertrophy: should it be reduced?

Left ventricular hypertrophy (LVH) is a structural adaptation of the heart to sustained hypertension, serving to normalize increased wall stress. Recent clinical studies have indicated that LVH is a powerful pressure-independent risk factor for cardiovascular morbidity and mortality, particularly sudden death, acute myocardial infarction, and congestive failure. The pathophysiologic sequelae of LVH consist of reduced ventricular filling and contractility, ventricular dysrhythmias, and diminished coronary reserve or myocardial ischemia. LVH can be reduced by antihypertensive therapy, although not all drugs are equipotent in this regard. Angiotensin-converting enzyme (ACE) inhibition seems to be the most powerful monotherapeutic modality for reducing LVH. Recent studies have shown that such a reduction also improves the pathophysiologic sequelae of LVH and maintains left ventricular pump function. Although the reversal of these pathophysiologic events is encouraging, it remains unknown whether reducing LVH will ultimately decrease the excessive risk of sudden death, acute myocardial infarction, and congestive heart failure that has been associated with this disorder independently of arterial pressure.

Does a reduction in left ventricular hypertrophy reduce cardiovascular morbidity and mortality?

Left ventricular hypertrophy is an important risk factor for sudden death and other cardiovascular morbidity and mortality irrespective of the level of arterial blood pressure. Left ventricular hypertrophy, i.e. an increase in wall thickness at the expense of left ventricular volume, is an adaptive mechanism observed in patients with long standing arterial hypertension. Severe left ventricular hypertrophy is associated with a reduction in left ventricular compliance, impaired coronary reserve, ventricular ectopy, and impaired contractile function. Left ventricular hypertrophy can be reduced by antihypertensive therapy; however, not all antihypertensive agents have the same effect on left ventricular hypertrophy despite their similar effects on arterial blood pressure. Angiotensin converting enzyme (ACE) inhibitors appear to be the most powerful agents for reducing left ventricular hypertrophy, followed by the nondihydropyridine calcium antagonists. In addition to reducing left ventricular mass and arterial blood pressure, certain calcium antagonists also improve left ventricular filling, suppress ventricular ectopy, and maintain or enhance contractile function. However, despite these beneficial effects, it is not known whether the risk of cardiovascular morbidity and mortality can be prevented or reduced by specific antihypertensive agents.

Cardiac hypertrophy due to pressure and volume overload: distinctly different biological phenomena?

Myocardial hypertrophy is a morphological adaptive response to chronic work overload imposed on the heart. It has been categorized into two distinct basic types: concentric hypertrophy, occurring in response to a sustained pressure overload in which wall thickness increases without chamber enlargement, and eccentric hypertrophy, in response to a chronic volume overload in which chamber volume enlarges without a relative increase in its wall thickness. It should be emphasized, in this context, that these adjectives are somewhat confusing, since the hypertrophy observed is not eccentric in the fashion often seen in the left ventricle of patients with hypertrophic cardiomyopathy. In fact, the hypertrophy is concentric in both instances, but is associated with an increase in chamber volume when described as eccentric, yet occurring with a maintained volume when said to be concentric. In rats made anemic by iron deficiency, the volume overloaded heart achieves an adaptive increase in mass characterized as hypertrophy occurring in the setting of dilated ventricle. This so-called eccentric hypertrophy depends on catecholamines as possible signals for myocardial growth, and progresses with preserved ultrastructure and contractile performance of the cardiac muscle. A gradually imposed volume overload results in a harmonious growth of the heart (it retains a relative normal shape, becoming a magnified normal heart), probably mediated by release of catecholamines into the myocardium. This process resembles the normal cardiac growth in response to the obligatory volume load imposed by an increasing cardiac output (greater metabolic demands) and blood volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular responses to experimental aortic coarctation in growing puppies

The haemodynamic status of 8 coarctated and 7 sham-operated beagle puppies was studied by a catheterization technique at rest and during isoproterenol and volume loading at the ages of 7 (I) and 9 (II) months (5 and 7 months after the experimental coarctation). Proximal aortic systolic and pulse pressures were constantly higher in the coarctation group than in the control group (P less than 0.05), and the systolic pressure gradient across the coarctation was always significantly higher in the coarctation group [I at rest mean 45 +/- 5 (SD) vs 5 +/- 4 mmHg, P less than 0.001, and after I isoproterenol infusion 56 +/- 9 vs 10 +/- 6 mmHg, P less than 0.001, and after I dextran infusion 58 +/- 10 vs 8 +/- 7 mmHg, P less than 0.001]. The time constant of exponential isovolumic left ventricular pressure fall after the isoproterenol tests was longer in the coarctation group (I 28 +/- 8 ms and II, 30 +/- 4 ms) than in the control group (I, 21 +/- 2, P less than 0.05 and II, 19 +/- 3 ms, P less than 0.005), indicating impaired relaxation. The tension time index during the volume loading tests increased in the coarctation dogs (I, 4150 +/- 660 and II, 4080 +/- 810 mmHg s min-1) to higher levels than in the control group (I, 3550 +/- 220, II, 2540 +/- 1140 mmHg s min-1, P less than 0.05 both). Cardiac output, left ventricular end diastolic pressure, inotropic parameters and heart rate were similar in both groups during the infusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Size dependence of the end-systolic stress/volume ratio in humans: implications for the evaluation of myocardial contractile performance in pressure and volume overload

The end-systolic stress/volume ratio is currently recognized as a relatively load-independent index of myocardial contractile performance, but its dependence on ventricular size may limit its value for interpatient comparisons. In this study, the relation between the end-systolic stress/volume ratio and left ventricular end-diastolic volume was angiographically analyzed in 104 patients with normal coronary angiograms. Eighteen patients had a normal ventricle, 24 had aortic stenosis, 18 had aortic regurgitation, 9 had mitral regurgitation and 35 had cardiomyopathy. An inverse relation between the end-systolic stress/volume ratio and left ventricular end-diastolic volume was demonstrated in the normal group (r = 0.72, p less than 0.001); subjects with a larger left ventricle had a reduced index but, presumably, the same degree of contractility as that of subjects with a smaller ventricle. Attempts to normalize values by using end-diastolic volume or body surface area were unsuccessful. A similar inverse relation was demonstrated in the aortic stenosis group (r = 0.48, p less than 0.05), probably because hypertrophy helps to keep wall stress normal or low despite progressive ventricular enlargement in these patients. The end-systolic stress/volume ratio was also inversely related to left ventricular chamber size in patients with volume overload due to aortic regurgitation (r = 0.80, p less than 0.001) and in those with cardiomyopathy (r = 0.84, p less than 0.001). However, at a given left ventricular end-diastolic volume, the end-systolic stress/volume ratio was higher in patients with aortic regurgitation than in those with cardiomyopathy, suggesting better contractile performance for a comparable degree of ventricular dilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Systolic and diastolic properties of the human left ventricle during valve replacement for chronic mitral regurgitation

M mode and two dimensional echocardiography were combined with pressure-flow data to analyze systolic mechanics and diastolic compliance in nine patients during valve replacement for chronic mitral regurgitation. Both M mode (six patients) and two dimensional (four patients) echographic analyses revealed large decreases in early postoperative shortening fraction (-24 +/- 17 [standard deviation] percent M mode study, p < 0.01: -30 +/- 12 percent two dimensional study, p < 0.02), which were significantly different from small changes observed in control subjects (M mode study, +7 +/- 10 percent, 25 subjects and two dimensional study, -7 +/- 14 percent, 8 subjects). Additional data suggest that ventricular compliance is increased in chronic mitral regurgitation and that elimination of the low impedance left atrial pathway by valve replacement is associated with a significant increase in wall stress (five patients, p < 0.02) that appears to be responsible for the decreased ejection fraction postoperatively. Analysis of hemodynamic variables other than ejection fraction and rate of circumferential shortening revealed no difference between five postoperative patients with chronic mitral regurgitation and five with coronary artery disease. These results in human subjects confirm predictions from studies in animal models and suggest that unique properties of chronic mitral regurgitation and demand special attention when patients with this condition are being evaluated for surgery.

Left ventricular responses to a program of lower-limb strength training

Nine healthy male subjects ages 18-27 exercised five days per week. Three days per week they performed five repetitions of squats, leg extensions and leg flexions with maximal resistance for a total of 11 sets. On the other two days each week subjects performed five leg presses and 20 calf raises with maximal resistance. Resting echocardiograms and physiologic evaluations were made prior to starting the strength training and again after ten weeks of training. Resting heart rate +/- SEM before and after training was 65 +/- 2 and 58 +/- 1.7 beats/min (P < .001). Maximal O2 uptake did not change significantly. Left ventricular wall thickness +/- SEM before and after training increased from 0.76 +/- .02 to 0.85 +/- 0.04 cm (P < .05). Left ventricular mass +/- SEM increased from 81.9 +/- 5 to 92.3 +/- 3.7 g (P < .05). The percentage of left ventricular fractional shortening +/- SEM increased from 32 percent +/- 1.2 to 36 percent +/- .9 (P < .001). Lower limb strength training in normal subjects did not increase maximal O2 uptake, but did induce increases in left ventricular wall thickness similar to that seen in champion strength-trained athletes. In addition, improvement in left ventricular performance without significant changes in left ventricular volumes was also observed.

Cardiac performance in hypertension re-evaluated through a combined haemodynamic ultrasonic method

From echocardiographic measurements, 39 patients with established, uncomplicated primary hypertension (diastolic pressure > 100 mmHg) were classified as follows: normal-sized heart (group 1, 10 cases); concentric left ventricular hypertrophy (group 2, 18 cases); left ventricular hypertrophy and cavity enlargement (group 3, 11 cases). Eighteen age-matched healthy subjects were investigated as a control group. Systolic and diastolic arterial pressure increased progressively from group 1 to 2 to 3. Left ventricular function, assessed from the relation between diastolic diameter and stroke index, was maintained in group 1, increased in group 2 (in spite of the greater pressure load), and reduced in group 3, in comparison with controls. Similarly, the mean velocity of circumferential fibre shortening (VCF) was normal in group 1, significantly increased in group 2, and reduced in group 3. It was impossible to discern whether the different behaviour of VCF in group 2 and in group 3 reflected opposite changes in ventricular contractility, or in wall stress during ejection, or in both. At variance with previous conclusions (which were based on utilisation of electrocardiographic and chest x-ray criteria to define hypertrophy) it is suggested that left ventricular concentric hypertrophy in man consequent to sustained hypertension is associated with an improved function. Whether this feature depends upon an augmented contractility or a ventricular unloading effect related to hypertrophy remains uncertain.

Anatomy of coronary arteries in univentricular hearts and its surgical implications

The coronary arterial anatomy in 26 univentricular hearts, its relation to the morphologic characteristics of the ventricles and rudimentary chambers, and its surgical implications were analyzed. All of the hearts except two had been operated on; 18 had septation with or without an extracardiac conduit and 6 had had palliative procedures. Twenty-one univentricular hearts with a left ventricular type main chamber had an anterior outlet chamber (17 left-sided subaortic, 3 right-sided subaortic and 1 right-sided subpulmonary). Right and left delimiting arteries outlined the outlet chamber in 16 hearts (76 percent). In 20 of the 21 hearts, large delimiting parallel branches of the right coronary artery course over the anterior wall of the heart; 13 of these vessels had been injured surgically with resultant ischemic myocardial necrosis. Five univentricular hearts did not have an outlet chamber; two had a left ventricular type main chamber and three had a morphologically right ventricular main chamber. Three of the five hearts had rudimentary pouches, located anteriorly in one and posteriorly in two. The two rudimentary pouches lying posteriorly were not outlined by delimiting arteries. Two of the five univentricular hearts without an outlet chamber also had injured coronary arteries. Thus, the identification of outlet chambers and rudimentary pouches in univentricular hearts is facilitated by the determination of coronary anatomy. The presence of major delimiting parallel branches over the usually favored ventriculotomy sites renders them vulnerable to surgical injury; such mishaps occurred in 15 of the 24 hearts that had either corrective or palliative operations.

Left ventricular performance in patients with left ventricular hypertrophy caused by systemic arterial hypertension

To assess the adaptation of the left ventricle to a chronic pressure overload we used echocardiography to study 18 patients with left ventricular hypertrophy caused by systemic arterial hypertension. Increased values for either posterior wall or interventricular septal thickness or both confirmed the presence of left ventricular hypertrophy in all patients and an increase in the average wall thickness to radius ratio was consistent with the development of concentric hypertrophy. No patient had clinical evidence of ischaemic heart disease. Ejection phase indices of left ventricular performance (mean Vcf, fractional per cent of shortening, normalised posterior wall velocity, and ejection fraction) were within the normal range in the basal state in 16 of the 18 patients. The hypothesis is advanced that patients with concentric left ventricular hypertrophy resulting from systemic arterial hypertension usually have normal left ventricular performance in the basal state because values for wall stress remain within the normal range. We conclude that the hypertrophic response to a chronic increase in systemic arterial pressure does not per se result in depression of the basal inotropic state of the left ventricle.

Transmural distribution of myocardial blood flow and of coronary reserve in canine left ventricular hypertrophy

Left ventricular hypertrophy was induced by banding of the ascending aorta in pupies at the age of 6 weeks. At the age of one year left ventricular weight per body weight was increased by 87% compared to control litter mates. While myocardial perfusion and myocardial oxygen consumption per 100 g were identical in the hypertrophy and control group, there was a significantly diminshed ratio of subendocardial/subepicardial flow in the hypertrophy group during moderate exercise. With maximal coronary dilation subendocardial diastolic resistance (mm Hg/ml-min-1 per 100 g) was 0.16 +/- 0.03 in the control group and 0.26 +/- 0.03 in the hypertrophy group. This diminished coronary reserve indicates an insufficient growth of the vascular bed in these hypertrophied hearts.