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

Abstract

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.

Postextrasystolic transient contractile alternans in canine hearts

“…Our observation contrasts with the general belief that exponential decay is the most representative type of postextrasystolic potentiation even in normal hearts [1,2,[17][18][19] and that the alternans decay is rare in normal hearts [3][4][5][6][7][8]. The transient postextrasystolic alternans has been reported to appear predominantly under such cardiac conditions as cardiac failure, ischemia, overload, tachycardia, and hypothermia, similar to the sustained pulsus alternans [3,4,[6][7][8][20][21][22][23][24].…”

“…The transient postextrasystolic alternans has been reported to appear predominantly under such cardiac conditions as cardiac failure, ischemia, overload, tachycardia, and hypothermia, similar to the sustained pulsus alternans [3,4,[6][7][8][20][21][22][23][24]. Therefore, the alternans decay that we have documented in this study is intriguing because the blood-perfused hearts that we analyzed did not seem to have abnormal mechanoenergetics despite excision and cross circulation [9][10][11][12][13].…”

“…Transient mechanical alternans has been documented as an atypical type of postextrasystolic potentiation in mammalian hearts including human hearts [3][4][5][6][7][8], and it has usually been observed under abnormal conditions such as cardiac failure, ischemia, overload, tachycardia, and hypothermia [3][4][5][6][7][8].…”