The demonstration of alternating contractile state in pulsus alternans

Abstract

A B S T R A C T Pulsus alternans was induced in 11anesthetized, open-chest dogs by rapid atrial pacing, and the left ventricular filling characteristics and lengthtension-velocity relationship of alternating beats were compared. The end-diastolic circumferences (circ) of the strong beats were slightly, but significantly, increased over the weak beats (7.3 > 6.9 cm, P < 0.01), confirming that diastolic filling does alternate in pulsus alternans. This alternation in initial fiber length seemed to result from an alternation in the prior end-systolic length, rather than from an alternation in diastolic filling time or compliance. There was also no difference in enddiastolic tension as measured by an isometric strain gauge suggesting no difference in contractile element relaxation before weak and strong beats.The contractile state of the strong beats was consistently greater than that of the weak beats when contractility was defined in terms of: (a) Vmax (3.13 > 2.53 circ/sec, P <0.01); and (b) the velocity of circumferential fiber shortening (0.84 > 0.39 circ/sec, P < 0.001) and developed tension (82.5 > 74 g/cm, P < 0.01) at isolength. The length-tension-velocity relationship of the left ventricle also varied between strong and weak beats when: (a) the maximum velocity of contractile element shortening at least common tension (1.68> 1.28 circ/sec, P <0.05); and (b) the velocity of circumferential fiber shortening (0.81 > 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

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

“…A variation in contractility between strong and weak had been described by the study of Vmax and Vc~ in open-chest dogs with pulsus alternans obtained by rapid pacing (14) but these beats were not compared to control beats. As compared with the beats preceding the premature ventricular contraction, in hypoxic regions, the strong beats appear as potentiated and the weak beats appear as attenuated.…”

“…It has been shown (10) that for the same level of inotropic state, endsystolic length is shorter with a decreased systolic pressure; in the weak beats, systolic pressure was lower and % systolic shortening was significantly decreased which indicates thus a decreased inotropic state. In most of the experiments (1,4,8,11,14) pulsus alternans is produced by rapid pacing of the heart which produces by itself a potentiation of contraction (9) which makes difficult the comparison between beats of pulsus alternans and previous beats. A variation in contractility between strong and weak had been described by the study of Vmax and Vc~ in open-chest dogs with pulsus alternans obtained by rapid pacing (14) but these beats were not compared to control beats.…”

Stability analysis of one-dimensional dynamical systems applied to an isolated beating heart

“…Finally, the concept that MP can be induced in a heart in which contractile characteristics (F., L., V.) are time invariant is in contrast with the commonly held explanation that suggests that time variant values for these parameters (Cohn et al, 1967;Noble & Nutter, 1970;McGaughey et al, 1985) cause MP. However, our analysis cannot predict MP of pathologies as emphysema or pericardial tamponade, where values of mechanical or hemodynamic characteristics are time variant.…”

“…Our results provide qualitative and quantitative predictions which can be used for comprehensive experimental design. (Back, 1977;Janz, 1982;Kim et al, 1985;Beyar & Sideman, 1986 (Gleason & Braunwald, 1962;Noble & Nutter, 1970;Guntheroth, 1982;Laskey et al, 1983;McGaugher et al, 1985). Recently, (Adler et al, 1985;Adler & Mahler, 1987) have modeled the beating heart as a dynamical system, using only certain aspects of the heart's functions.…”

Mechanism of sustained mechanical alternans. Effect of variations in ventricular billing volume.

“…10 It also has been demonstrated that when EDV is greater before the strong beat, significant variations in end-diastolic pressure (EDP) 13 Figure 2, we chose slopes of 0.8 and 0.9 to represent the real cases. Obviously, the same conclusions would be obtained if parallel slopes with the exact value of 1, or any other value, were plotted.…”