- R J Shephard: School of Physical and Health Education, Department of Preventive Medicine and Biostatistics, Faculty of Medicine, University of Toronto, Ontario, Canada.
Congestive heart failure is a widely prevalent sequel to myocardial infarction and other chronic conditions (including ischaemia without infarction, hypertension, various infections, toxic metabolic and endocrine disorders). Exercise tolerance is severely limited; the cardiac ejection fraction is often less than 20% and the peak oxygen intake may be less than 10 ml/kg x min, with a resulting deterioration in the quality of life. Possible factors contributing to the poor tolerance of exercise include: (i) disturbances of myocardial function (damage to the ventricular wall; decreased inotropic response, mitral valve regurgitation and increased diastolic pressures); (ii) peripheral vascular factors (decreased metaboreceptor discharge, reduced vasodilator response, increased activity of sympathetic afferents and less efficient distribution of cardiac output); (iii) hormonal disturbances (increases of catecholamines, renin/angiotensin/aldosterone, antidiuretic and natriuretic factors, endothelin and decreased endothelium-relaxing factor); (iv) impaired muscle function (loss of lean tissue, increase of type II fibres, increased impedance to perfusion, enzyme changes); (v) ventilatory disturbances (increased oxygen cost of activity, pulmonary congestion, increased ventilatory drive, mismatching of ventilation and perfusion, increased anaerobic effort); and (vi) psychological factors (anxiety, depression and iatrogenic limitation of effort). The prognosis with conventional treatment is poor, but patients with stable congestive heart failure respond favourably to a progressive exercise programme. Reported gains depend on the cause of congestive failure, initial status, study duration and compliance, and the type of training programme. Most studies to date have been short term (4 to 16 weeks), and relatively few have adopted a randomised controlled design. Suggested bases for the enhancement of aerobic performance of up to 20% include an increased intensity of peak effort, an enhanced matching of ventilation to perfusion, improved cardiac function, a strengthening of skeletal muscle and an increase of aerobic enzyme activity in the muscles. A few studies have continued for a year or longer and it appears that the gains realised over the first 16 weeks of training can be sustained for this period; the quality of life is enhanced, but data are as yet insufficient to judge effects upon mortality rates. Useful clinical information can be obtained from a 6-minute walk, but the choice for more precise evaluation lies between a measurement of ventilatory threshold or peak oxygen intake. Given initial muscle wasting, prescribed exercise should include both aerobic activity and resisted muscle exercises.