SUBACUTE BACTERIAL ENDOCARDITIS

Prior to the discovery of penicillin, subacute bacterial endocarditis was almost invariably fatal ; today, with efficient antibiotic treatment the picture is-entirely different and the majority of those affected may be saved. The mortality, and of almost equal importance the degree of residual disability, depend on two-factors—the stage at which treatment is begun and its thoroughness. If diag¬nosis is delayed for weeks, or months, irreparable damage to a valve may occur, so that even if healing results the heart may be so handicapped that progressive cardiac failure is inevitable. Further, the disease once firmly established becomes more difficult to eradicate. As regards thoroughness of treatment, there is ample evidence that short courses of penicillin for two or three weeks, while yielding a high initial recovery rate, are associated with a considerable relapse rate and a bad overall prognosis.
Early treatment presupposes early diagnosis, and this in turn depends on the diagnostic acumen of the individual doctor. Cases of subacute bacterial endocarditis, like those of every other disease, come first under the observation of the general practitioner, and it is he who should consider this possibility in every case of obscure or unexplained fever occurring in a patient known to suffer from rheumatic or congenital heart disease. The disease may occur with no history or signs of a valvular lesion, especially when the infection has become implanted on a congenital bicuspid aortic valve. A further group of cases is now being diagnosed with increasing frequency, namely in adults over the age of fifty, in whom unhappily the diagnosis is commonly not suspected until the disease is far advanced.
The diagnosis of subacute bacterial endocarditis may be missed in cases of congenital heart disease with a left-to-right shunt (ventricular septal defect, patent ductus arteriosus) since in these emboli are carried not to the systemic circulation but to the lungs, and the characteristic peripheral embolic phenomena so common in the rheumatic case are lacking. Such patients may suffer repeated episodes of respiratory illness, a curious recurrent pneumonic condition, the significance of which may be overlooked. Diagnosis may be further complicated by the injudicious use of penicillin or other antibiotics. These, given in short courses for apparently minor infections, may for a time control fever and inflammation, so that the possibility of subacute bacterial endocarditis may not be considered, and even if it is the diagnosis may be discarded because blood cultures taken after antibiotics have been given are likely to be negative.
When a doctor suspects subacute bacterial endocarditis on clinical grounds ever}7 attempt should be made to isolate the organism. Repeated blood cultures should be undertaken, and a higher percentage of positive results will be obtained if these are done in series of three on any one day. A spike of temperature should suggest the withdrawal of blood for culture on three occasions at hourly or two-hourly intervals, and this process should be repeated on successive days till four or five batches have been sent for examination. No antibiotics should be
•administered until such tests have been carried out, but treatment should be started without delay as soon as the cultures have been taken.
The isolation of the organism and the determination of its sensitivity to penicillin and other antibiotics decide both the choice and the dose of antibiotic to be given. Not all cases are due to the Streptococcus viridans, a proportion being due to other organisms varying widely in resistance to penicillin. This is particularly true of S. fixcalis, a commonly highly resistant organism which
•may gain access to the blood stream from the urinary tract. In a proportion of patients no organism is isolated from the blood and a significant number of abacterial cases occur even when investigations are carefully carried out. The incidence is reduced if blood cultures are made sufficiently frequently and with
•appropriate techniques. These abacterial cases should not be denied vigorous treatment as soon as a number of blood cultures have been made.

Choice of Antibiotic, Dosage and Duration of Treatment.—For the average case from which a fully sensitive S. viridans has been isolated the standard course of treatment consists of the intramuscular injection of 5 million units of penicillin daily in divided doses, continued over a period of fifty-six days. It may seem cruel to inflict four or five painful needle pricks daily over a period of eight weeks, particularly to a child, but the author has still to be convinced that procaine penicillin or oral preparations of penicillin are equally effective ; the disease is of such gravity that it is imperative to pursue treatment in the most effective fashion. When the organism recovered is more resistant than usual this dosage may have to be increased even up to 20 million units daily, and an adjuvant antibiotic added, for which purpose streptomycin, i g. daily by intra¬muscular injection, is usually the drug of choice. The broad-spectrum oral antibiotics of the tetracycline group are not of great value in treatment of subacute bacterial endocarditis, though on occasion an organism may be recovered which is sensitive to one member of the group and resistant to penicillin or streptomycin. When a very high blood level of penicillin is desired the renal tubular-blocking action of probenecid (p. 59) may be employed. The desired result is achieved without greatly increasing the dose of antibiotic.
General Treatment.—The general treatment of a patient with subacute bacterial endocarditis is that for any febrile infective illness, modified by the severity of the cardiac lesions present. In the patient whose valves are so grossly damaged and whose heart muscle is so poisoned by toxeemia that he is in cardiac failure, complete rest and treatment along standard lines for congestive heart failure will be required for weeks or months. Angemia and malnutrition must be treated appropriately. Those patients in whom the infection has been diagnosed and treated at an early stage, and in whom cardiac enlargement and valve damage are minimal and failure absent, need only be kept in bed for two to three weeks, after w^hich a progressive increase in activity may be allowed.
Embolism.—Major embolic accidents, affecting the cerebral circulation or other important systemic arteries, are frequent and account for a considerable proportion of fatalities. Such accidents are unfortunately not reduced by anti-coagulants which have no place in the treatment of this disease. Death from embolism is most likely to occur in patients with large crumbling vegetations— that is in patients who have suffered from the disease for a considerable period before a correct diagnosis has been made and treatment commenced. The over¬all mortality from these embolic accidents is of the order of 10 per cent.
Prophylaxis—Septic Foci.—Every patient with known rheumatic or congenital heart disease should be subjected to regular dental survey so that early sepsis can be detected and dealt with. No such patient should be permitted to have a dead crowned tooth, since apical infection in such a case is probable and may escape notice since it may be painless. Dental extractions should always be carried out under protection with soluble penicillin administered by injection an hour or two before and for two or three days after the dental operation. Similarly, infections of the urinary tract in such individuals should be efficiently treated, since it is known that S. fcecalis may gain entry to the blood stream from such a focus. Patients under treatment for subacute bacterial endocarditis should also be carefully investigated for septic foci and if these are found they should be dealt with while the patient is under the protection of an antibiotic. Failure to eliminate a septic focus may lead to repeated re-infection and relapse of the endocarditis.
Prognosis.—Even with efficient treatment the prognosis varies considerably with the stage at which treatment is begun. The overall recovery rate today is of the order of 75 per cent. Patients diagnosed and treated at a late stage and who may already be in cardiac failure, have a much worse prognosis, the recovery rate being 50 per cent. or less, and the survivors tend to lapse at an early date into cardiac failure. When patients are treated at an early stage the recovery rate is of the order of 90 per cent. and residual disability may be slight. It cannot be too strongly emphasized that to obtain the best results early diagnosis and efficient treatment are imperative.