THE NATURE OF VENTRICULAR ALTERNATION RESULTING FROM REDUCED CORONARY BLOOD FLOW

Abstract

Typical ventricular alternation (pulsus altemans) was produced by periodic deprivation of blood flow to the region of the left ventricle supplied by the ramus descendens anterior, and the changes in contraction of this region were studied by a myocardiographic method. The records so obtained showed that the region of impaired blood supply may merely contract less efficiently during the smaller beat or it may fail to contract at all, whereas in the larger beat it may contract normally or it may be depressed but not to so great an extent as in the small beat. The fact that in some expts. contractions alternately occurred and failed in large regions of ischemic muscles offers substantial support for the view that similar omission of contractions in more distributed fractions accounts for alternation affecting an entire ventricle or the whole heart. The possibility of such regional alternation must be considered in experimental studies of the alternans problem and certainly in every clinical case. Since alternate shortening and extension also accompanied large and small beats initiated by a sudden long diastolic pause and since the degree of stretch was greater in the small beats, it follows that the time required for recuperation, rather than dynamic changes in diastolic size or tension, is the factor dominantly concerned in evoking such temporary alternation. It is questionable whether any form of alternation can occur without periodic diminution or absence of contraction in some fractions of ventricular muscle.