HEART, DISEASES OF THE. Diseases of the heart may be classified in two main groups :
Disease of the valves; and (2) Disease of the walls of the heart.
(1.) Valvular Disease.—Inflammation of the valves of the heart, or endocarditis, is the most common complication of rheu matism in children and young adults. More severe types, which are apt to prove fatal from a form of blood poisoning, may result when the valves are attacked by pneumococci, pyogenic strep tococci and staphylococci, gonococci, or influenza bacilli. As a result of endocarditis, one or more of the valves may be damaged, so that it leaks, the aortic and mitral valves being affected far more commonly than those of the right side. In the process of healing, scar tissue is formed which has a tendency to contract, so that in some cases the orifice of the valve becomes narrowed. We may thus have incompetence or stenosis of a valve or both combined.
Valvular lesions are detected on auscultation by the blowing sounds or murmurs to which they give rise. Thus, lesions of the mitral valve give rise to murmurs heard at the apex beat, and lesions of the aortic valves to murmurs heard in the second right inter-costal space. Accurate timing of the murmurs in relation to the heart sounds indicates whether the murmur is due to steno sis or incompetence. If the valvular lesion is severe, changes must take place in the heart cavities and muscle to compensate for the effects of the regurgitation or obstruction, as the case may be, or the circulation would fail. In affections of the aortic valve, the extra work falls on the left ventricle, which dilates and hyper trophies. In affections of the mitral valve the effect is felt primarily by the left auricle, a thin walled structure incapable of undergoing the requisite increase in power to resist the back ward flow through the mitral orifice in case of leakage, or to overcome the effects of obstruction in case of stenosis. The back pressure is therefore transmitted to the pulmonary circulation, and as the right ventricle is responsible for maintaining the flow of blood through the lungs, the strain and extra work fall on the right ventricle, which in turn dilates and hypertrophies. The degree of hypertrophy of the left or right ventricle is thus, up to a point, a measure of the extent of the lesion of the aortic or mitral valve respectively. When the effects of the valvular lesion are so neutralized by these structural changes in the heart that the circulation is equably maintained, "compensation" is said to be efficient.
When the heart gives way under the strain, compensation is said to break down, and dropsy, shortness of breath, cough and cyanosis are among the distressing symptoms which may set in. The mere existence of a valvular lesion is unimportant if com pensation is efficient, and many persons with slight valvular lesions are living lives indistinguishable from those of their neighbours. But with more serious lesions certain precautions should be observed in regard to over-exertion, excitement, over-indulgence in tobacco or alcohol, etc., as additional strain on the heart may cause a breakdown of compensation. When this occurs treatment is required. Rest in bed may be sufficient or may need to be supplemented by drugs such as digitalis, convallaria or strychnine.
(2.) Affections of the Muscular Wall of the Heart.— Dilatation of the heart is an incident in the earlier stages of valvular disease antecedent to hypertrophy. Temporary dilatation of the heart occurs in violent exertion, but rapidly subsides and is not harmful to the sound and vigorous heart of the young. But if the heart muscle is weak and flabby from a too sedentary life or from degenerative changes, or during convalescence from a severe illness, circumstances which will not injure a healthy heart, may give rise to serious dilatation from which recovery may be protracted. Influenza is a common cause of cardiac dilatation after the acute illness has subsided, if the patient resumes his ordinary life too soon. Fatty or fibroid degeneration of the heart wall may occur in later life if the nutrient blood-vessels are the seat of arteriosclerosis or atheroma. The affection known as angina pectoris (q.v.) may be a further consequence of this de fective blood-supply.
The treatment varies according to the nature of the case. In serious cases of dilatation, rest in bed, purgatives and cardiac tonics will be required.
In commencing degenerative change the Oertel treatment, con sisting of graduated exercise up a gentle slope, limitation of fluids and a special diet, may be indicated. In cases of slight dilatation after influenza or recent illness, the Schott treatment by baths and exercises as carried out at Nauheim is sometimes beneficial.
Disorders of Rhythm of the Heart's Action.—Under this heading may be grouped a number of conditions concerning which much has been learned during the past 20 years by the researches of the late Sir James Mackenzie and Sir Thomas Lewis. By means of Mackenzie's ink polygraph or Lewis's modification a pro longed simultaneous record of the arterial and venous pulses can be obtained.
Electrical records of the heart beat have given even more accurate results. It has long been known that a minute electrical current is generated when the heart, or any other muscle, contracts. In 1903 Einthoven, of Leyden, invented his string galvanometer (q.v.) an instrument capable of detecting a current of less than 6 0 05 millionth of an ampere. By putting the human heart in electrical connection with the instrument, either by means of contacts from the chest wall in front of the heart, or, more conveniently, by three electrodes in which the two hands and one foot are immersed, a graphic curve is obtained of the electrical variations associated with each heart beat together with appropriate time marks. On such a curve the variations due to auricular and ventricular contraction respectively are dif ferentiated, the wave representing auricular contraction being designated arbitrarily as "P," and that representing the commence ment of ventricular contraction "R." The time interval between these two components of each normal heart beat can be measured accurately.
In health this time interval is between o• I 8 to 0.20 sec.; if the junctional tissues between auricle and ventricle are injured, either by disease or by cardiac poisons, conduction between auricle and ventricle is delayed and the "P.R." interval may become 0.24 sec., or even more. This state of affairs is known as heart block, and in its minor stages can be recognized only by means of graphic records. With more severe damage of the junc tional tissues, higher grades of auriculo-ventricular block ensue ; thus the ventricle may respond only to every alternate, or to every third or fourth auricular beat. In complete heart block no stimuli reach ventricle from auricle and there is complete dissociation be tween the upper and lower chambers of the heart, the former beat ing at their usual rate of 6o-8o per min. while the ventricles take on a rhythm of their own, usually at a rate of about 35-4o. The presence of these more serious grades of heart block can often be surmised on clinical grounds, but graphic records are essential for their certain recognition. Heart .block is one of the rarer causes of irregular heart action.
There are some other causes of cardiac arrhythmia, some of which are unimportant, others serious. Quite early in the century it was impossible to differentiate with cer tainty between the two types. Now differentiation can be made with confidence, and often without the necessity for taking poly graphic or electrocardiographic tracings. For instance, "intermis sions" of the pulse and "premature beats" were considered to be serious. Nowadays it is recognized that, in themselves, they are not serious but are almost invariably present from time to time in most elderly subjects.
But there is another common type of cardiac arrhythmia known as auricular fibrillation which is un doubtedly serious. Here, as a result of pathological changes in the heart muscle, the auricles cease to contract rhythmically as a whole in a series of orderly beats; but the auricular musculature is in a constant state of incoordinate and futile twitchings. In consequence, the ventricles, instead of being stimulated from above rhythmically at the rate of about 7o per min. are over whelmed by a series of stimuli which pour down on them like an avalanche. They do their best to respond, and contract rapidly and irregularly at a rate of I20-18o per minute. This condition is very constantly associated with cardiac failure, usually ending in dropsy, shortness of breath and eventually, if progressive, in death. It is a dangerous condition, but when recognized (and about its recognition there is now seldom any difficulty) it may be controlled by the administration of digitalis. This drug depresses the conductivity between auricle and ventricle, and consequently only the more powerful auricular stimuli reach the ventricle after its use ; the ventricle now beats, still irregularly, but more slowly, and consequently, having time for a longer rest between each beat, more powerfully. The auricles may fibrillate in paroxysms lasting a few minutes, hours or days ; but more commonly the condition is a permanent one. It brings about great disability, but, if controlled by the use of digitalis and if the patient is content to live within his limits, it is often compatible with 1o, 15 or even 20 years of very fair health.
Lewis has recently demonstrated by means of the string galvanometer that in auricular fibrillation, as in its sister condition, auricular flutter, instead of each auricular beat arising in the sinu-auricular node and radiating thence throughout the auricles, a "circus movement" takes place in the auricular muscle, often around the mouths of the great veins en tering the right auricle. We have to conceive of an irregular wave of contraction whirling around, usually in an irregular circle. From this contractile path are projected into the surrounding auricular muscle countless stimulating impulses, very much as sparks are thrown out from a catherine wheel, and, as a result, the whole of the auricular musculature is thrown into incessant, shimmering contractions. So soon as this explanation of auricular fibrillation was put forward and accepted, it was manifest that, if we could bridge the gap between the advancing crest, and the retreating wake of the contracting wave in its "circus," the heart might revert to normal rhythm. It has been found that quinine and its allied alkaloids, of which quinidine is the one usually em ployed, have such an effect. In rather more than 5o% of cases of auricular fibrillation it is possible to bring about a reversion to normal rhythm by the use of quinidine. Unfortunately the process is not devoid of risk, and many cases relapse into fibrillation when quinidine is withdrawn.
Here the heart beats with great rapidity (rates of 150-200 per min.), but regularly. There is an abrupt transition from the normal and slow, to the abnormal and rapid rhythm ; the attack may last for a few seconds, or for a few days, and ends as abruptly as it began. Such attacks may be asso ciated with great respiratory and mental distress, and may lead to cardiac failure. Their differentiation from a purely nervous form of rapid heart action may be impossible without an electro cardiogram taken during both normal and abnormal periods.
In some healthy persons the rate of heart beat is unusually slow. In jaundice a slow pulse rate is the rule.
Of recent years X-rays have been used extensively in the investigation of cardiac disease. By their help alone can accurate information be obtained of the size of the heart and aorta. Percussion and location of the apex beat by the finger are often misleading.
The vital capacity is the maximal amount of air which an individual can expire from the lungs after taking the deepest possible inspiration. Disease of either heart or lungs may very materially diminish this quantity which falls or rises accord ing as the disease advances or tends to recovery. Estimation of the vital capacity, therefore, is a means of recording numerically a functional disability and its progress. The trend of recent in strumental investigation of the heart's action has been to stress the importance of the heart's muscle in cardiac pathology and to minimise the effect of valvular lesions, to which so much attention was formerly paid. Possibly the pendulum has swung a little too far in this direction but it is certain that many cardiac murmurs heard through the stethoscope are not necessarily indicative of valvular or of any other disease. The innocuous nature of these "exo-cardial," "cardio-respiratory," or "haemic" murmurs, had long been known to the more experienced physicians, but it re quired the mass experiment of the World War to teach the lesson to the rank and file of the profession.
In Dec. 1925 Yandel Henderson, of Yale university, published a comparatively simple method of determining the output of the heart per beat. From this it is easy to calculate the actual work done by the heart, and to recognize departures from normal efficiency. Thus we now appear to have a simple method of ascer taining with accuracy whether a heart is functioning normally or not, and whether a defect previously discovered is stationary, im proving or deteriorating.
