GENETIC ASPECTS OF CARDIOVASCULAR DISEASES IN ANIMALS

When the incidences and types of cardiovascular disease present in various species, breeds, and strains, or families of animals are compared, certain differences are apparent. It is often difficult, however, to separate hereditary from environmental influences.

Studies of vascular disease in zoo animals have shown that changing environmental conditions can alter the incidence of certain types of lesions in various species. Species differences, however, in resistance to diet-induced atherosclerosis appear to be genetically determined. The prevalence and types of congenital cardiac malformations appear to differ from species to species, but further systematic study is required. Arterial blood pressure is higher in the giraffe and turkey than in other species, and normal variants in cardiac rhythm are characteristic of the dog, horse, and mole.

Relatively high incidences of specific cardiovascular diseases are found in certain breeds of animals. The White Carneaux, Autosexing King, and Silver King breeds of pigeons have a high incidence of atherosclerosis. Congenital heart disease appears to be more common in purebred than in mongrel dogs, and an unusual aggregation of cases of subaortic stenosis in the Boxer and German Shepherd breeds has been found. In a survey of heart disease in dogs, the prevalence of chronic congestive heart failure in the male Cocker Spaniel greatly exceeded that in the male and female of all other breeds. Arterial blood pressure is higher in Broad Breasted Bronze turkeys than in the Jersey Buff breed. This is associated in the former breed with a relatively high incidence of spontaneous aortic rupture.

The occurrence of cardiovascular disease is unusually high in certain families and strains of animals. Among swine, litter and strain differences in serum cholesterol levels and in susceptibility to atherogenic diets occur. The White Carneaux breed of pigeons is actually a highly inbred strain with a remarkable predisposition to the development of atherosclerosis. Strains of chickens and rats with high incidences of interventricular septal defects have been developed by selective breeding. The familial occurrence of congenital heart disease in dogs and swine has been observed, and an inherited vascular anomaly in cattle has been described. Through selective breeding of laboratory rodents, strains with various types of cardiomyopathies have been developed. Certain diseases thought to be similar to the heritable disorders of connective tissue in man have been identified in domestic species. The level of arterial blood pressure is a heritable characteristic, and strains of rabbits, rats, and chickens with relative hypertension have been produced by selective breeding.

Many of these observations indicate the importance of inheritance in determining susceptibility to various types of acquired cardiovascular disease. Genetic factors appear to operate in determining the occurrence of certain congenital malformations. Breeding experiments provide the most convincing evidence of genetic influence on the development of specific cardiovascular lesions. This experimental approach holds the greatest promise for furthering knowledge and understanding of the role of inheritance in the etiology of disease of the heart and blood vessels.

TRANSIENT BUNDLE-BRANCH BLOCK

Fourteen patients with transient bundle-branch block have been personally studied. All but one suffered from ischemic heart disease commonly accompanied by hypertension. The conduction defect was observed to appear during acute infarction, attacks of prolonged chest pain, and episodes of left ventricular failure. Not infrequently, however, the appearance and disappearance of bundle-branch block was unaccompanied by any recognizable change in the patient's physical condition.

Bundle-branch block may revert to normal intraventricular conduction after many years. In one patient bundle-branch block disappeared on three separate occasions after having been present for over 12 months. Another patient is described in whom normal conduction returned after left bundle-branch block had been established for a record duration of 6 years.

The etiology, prognosis, and pathogenesis of transient bundle-branch block have been discussed and the practical importance of this conduction defect in the electrocardiographic diagnosis of myocardial infarction is mentioned.

ARTIFICIAL RESPIRATION AND ARTIFICIAL CIRCULATION: TRAINING EXPERIENCES--PRINCIPLES AND PRACTICE OF EMERGENCY RESUSCITATION AND POST-RESUSCITATION CARE

A training program in the newer methods of treatment of acute cardiopulmonary emergencies which was developed at the University Hospital, University of Saskatchewan, is reported. Artificial respiration by the chance rescuer, primary and secondary resuscitation, and post-resuscitation measures involving the use of special drugs and equipment by trained personnel are described. Figures and tables designed for wall-mounting and ready reference in an emergency situation are presented. Firstaid ventilatory adjuncts for use by trained personnel are classified and critically appraised, and the propriety of their use is emphasized. A plea is made to the medical profession and allied agencies to assume the responsibility of spreading knowledge of the new techniques more widely. Unless effective treatment is instituted early enough to prevent death or permanent anoxic damage to heart and brain, follow-through therapy will often be fruitless.