Alteration of the heart occurs whenever any of its tissues, contractile or conductive, fail to function during alternate beats. This results in a diversity of 2:1 conduction blocks with electrical alternation and myocardial blocks that produce alternation of the pulse. In a general way, the more distal blocks, involving bundle branches, arborization, and myocardium are the more ominous, implying serious underlying heart disease. They can occur normally, however, at rapid heart rates.
Another type of alternation involving atrial as well as ventricular waves is sometimes seen in serious pericardial disease with effusion. It is believed to be due to an unusual rotary oscillation of the heart released from its normal inhibitory mediastinal restraints by the surrounding effusion. This is an anatomic rather than a cellular form of alternation and can exhibit other mechanical disorders such as alternating friction sounds.
- © 1963 American Heart Association, Inc.