Pulsus alternans in regionally hypoxic ventricles of open-chest dogs: regional mechanical alternation of potentiation and attenuation of the inotropic state.

Sustained mechanical alternation appeared after a spontaneous premature ventricular contraction in 6 open-chest dogs during the perfusion of the left circumflex coronary artery by Krebs-Henseleit solution equilibrated with 5% CO2 and 95% N2. The animals were instrumented with a catheter in the left ventricle and ultrasonic crystals in hypoxic and control segments. Left ventricular systolic pressure was significantly higher in the strong than in the weak beats with no significant difference of end-diastolic lengths in hypoxic and control segments. In hypoxic segments, systolic shortening was significantly larger in strong beats (11.9 +/- 1.9%) as compared with weak beats (5.1 +/- 1.6%) and with control beats preceding the premature ventricular contraction (9.7 +/- 1.6%) but the postextrasystolic beat was larger (17.9 +/- 1.3%). There was no significant change of systolic shortening in control segments during mechanical alternation which appears thus as a regional phenomenon which cannot be explained by the Starling mechanism: instead, alternation is attributed to a change of excitation-contraction coupling after a premature contraction with alternation of potentiation and attenuation of the inotropic state.