alternation

The occurrence of two things or phases in succession and recurrently; used interchangeably with alternans.

- cardiac a. the occurrence of any cardiac phenomenon every other beat.

- concordant a. a. in either the mechanical or electrical activity of the heart, occurring in both systemic and pulmonary circulations.

- discordant a. a. in cardiac activities of either the systemic or the pulmonary circulation, but not of both, or in both but oppositely directed in each.

- electrical a. of heart a disorder in which the ventricular or atrial complexes or both are regular in time but of alternating pattern; detected by electrocardiography. The P, PR segment, QRS, T, QRS-T, or P-QRST alternate singly or in combination.

- a. of generations a succession of generations of individuals like and unlike the original parents, or an a. of sexual and nonsexual generations.

- mechanical a. of the heart disorder in which contractions of the heart are regular but are alternately stronger and weaker.

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al·ter·na·tion (awl″tər-naґshən) [L. alternare to do by turns] the succession of two opposing or different events in turn.