It would, of course, be incorrect to attempt to draw conclusions as to the dangers and the chances of success of suture of cardiac wounds in man from the results obtained by animal experimentation. Animals are placed in very unfavorable conditions after the operation. They are very restless and cannot be kept quiet. Ideal cleanliness is impossible and the animals may infect their wound by rubbing the external wound against the dirt on the floor of their cage. From the animal mortality in these investigations no rigid inferences applicable to human beings can therefore be made.

Some conclusions of importance can, however, be drawn. Above all, my experiments seem to show that the mammalian heart will bear a much greater amount of manipulation than has hitherto been suspected. Very large wounds of the heart can heal and the healing process occurs in a manner entirely analogous to that in other muscular tissues. Even an extensive suture of the heart-wall of rabbits and dogs, although we know that thereby a large number of muscle fibres are destroyed and replaced by connective tissue, does not interfere with the function of the cardiac muscle as a whole.

Can some of the results in the above recorded experiments be, with some restrictions of course, applied to the human heart? I think that this question must be answered in the affirmative. If we compare the knowledge we possess of wounds of the heart in man, with that obtained from animal experiments, and find that they agree in all essential particulars, then we are justified in reasoning by analogy that suture of wounds of the heart in man will give results similar to those obtained in the animal. In the last few decades, the advances made in all the branches of medicine—especially in pathology, bacteriology and surgery—have been due to a great extent to the generalization of the results of animal experimentation. To the careful and critical investigator, the results obtained in the animal experiment have always been of the greatest value in indicating to him the possibility of results to be obtained by similar procedures in the human body.

From the study of wounds of the heart in man, and from the results obtained in my experiments, this conclusion seems therefore justified: wounds of the heart in man, when all other means have been tried and found wanting, can and ought to be closed by suture. The application itself of the suture is devoid of the one great danger that was feared in the past, i. e. of sudden arrest of the heart during the manipulations incident upon the application of the sutures. The number of sutures should be as small as possible so as to limit the amount of connective tissue which will be formed; for all the muscle fibres that are compressed by the sutures eventually atrophy and are replaced by new-formed connective tissue. It is probable that this connective tissue will not lead to degenerative changes in the heart-muscle. On the post-mortem table, fibrous plaques are often found in the otherwise normal human heart. In a number of the muscles of the body fibrous bands—tendinous intersections as they are called—are normally found. In the large number of microscopic sections of the heart-muscle that I have examined, I could find no evidence of pathological changes in the muscle fibres some distance from the scar. For similar reasons the suture should always be an interrupted one. We have shown that there are dangers and disadvantages in the continuous suture both on theoretical grounds and in practical use.

The sutures should be passed through as little of the heart substance as possible; if they penetrate the epicardium and a small part of the thickness of the heart-muscle it will generally be sufficient.

When the heart's action is not too rapid, each suture should be tied during a diastolic relaxation of the part under treatment. On this point we have not yet any experience in man. Cappelen, in his patient, tied the sutures during systole. Rehn tied them in his case during diastole. Only time and further experience will show how much importance is to be attached to this point. All that can be said, in the present state of our knowledge, is, that on theoretical grounds and from animal experimentation, it must be considered safest to tie the sutures during diastole.

On first sight, it might appear difficult to apply sutures to an organ in such constant motion as is the heart. In practice, however, the difficulties have been proven not to be so great as might appear.

The heart may be grasped with a forceps and the needle and suture easily passed. It is no more difficult to pass and tie a suture in a large dog than in a small rabbit. Hence we should infer that the difficulties of this procedure in the human heart, are not so great, a fact that has been borne out by the experience of those surgeons who have reported cases of heart-suture in man.

The cases will always be few in which this extreme method of treatment—for so we must style it—is necessary. Indeed, of the patients that come under the care of the surgeon, there are some who will recover from even large heart wounds without any local treatment at all. Cases have been recently reported by Conner, Brugnoli, Hamilton and others, where after wounds as large as three centimetres, the hæmorrhage ceased spontaneously and the patients recovered. One cannot say, therefore, that wounds larger than a certain size must always be sutured. Each case must be carefully considered by itself.

When we examine the nine cases of suture of the human heart in man (see pages 487 to 490) we cannot but hope for considerable success from this new method of surgical procedure. Of the nine cases, four recovered entirely, and four died of complications referable to other organs—quite an encouraging record in a few cases.

Finally, I may be permitted to summarize these conclusions as follows:

1. Suture of a wound of the heart as a final resort is an operation worthy of consideration in some cases and often justifiable.

2. Suture of wounds of the heart in animals, and also in man, is devoid of the danger of sudden arrest of the heart, due to the manipulation of the heart incident to the procedure, unless Kronecker's coördination centre be injured.

3. The suture should be an interrupted one of silk, applied in most cases so that the epicardium and superficial layers of the myocardium should be the only ones penetrated, and tied, when possible, during diastole.

4. No stated indications can be given as to the cases that are operable or the time when the operation should be done. Each case must be considered by itself for symptoms which would justify operative interference.

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