Pulsus alternans is primarily driven by a beat-to-beat alternation in the intrinsic contractile state of the myocardium, with secondary alternations in ventricular filling.
Pulsus alternans was induced in 11 anesthetized, open-chest dogs by rapid atrial pacing, and the left ventricular filling characteristics and length-tension-velocity relationship of alternating beats were compared. The end-diastolic circumferences (cire) of the strong beats were slightly, but significantly, increased over the weak beats (7.3 > 6.9 cm, P 2.53 circ/sec, P 0.39 circ/sec, P 74 g/cm, P 1.28 circ/sec, P 0.39 circ/sec, P < 0.001) at maximum developed tension were examined. Analysis of the length-tension-velocity characteristics of sequential beats at the onset of alternans in three dogs suggests that an alternation in contractility initiates alternans, with secondary alternations in ventricular filling. Cross-clamping of the aorta in three other dogs essentially eliminated the alternating changes in end-diastolic length and pressure, while the resultant isovolumic contractions continued to demonstrate clear evidence of pulsus alternans in the ventricular systolic pressure, suggesting the persistance of an alternating contractile state. The evidence suggests that an important mechanism in the production and propagation of pulsus alternans, as produced in the intact canine ventricle by rapid pacing, is a beat-to-beat alternation in contractile state with secondary alternations in ventricular filling.
Noble et al. (Mon,) studied this question.
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