Mechanics of pulsus alternans in aortic valve stenosis.

Differences in the mechanics of strong and weak contractions during sustained pulsus alternans were studied in 4 patients with aortic valve stenosis (AS). No significant difference was observed between strong (S) and weak (W) beats in M-mode echographic end-diastolic minor-axis dimension or end-diastolic meridional wall stress. Peak systolic meridional stress (S:225 X 10(3) dynes/cm2; W:205 X 10(3) dynes/cm2), the time integral of left ventricular (LV) meridional systolic stress (S:5,000 X 10(3) dynes/cm2; W:4,500 X 10(3) dynes/cm2) and the area of a stress dimension loop (S:202 X 10(3) dyne/cm; W 165 X 10(3) dyne/cm) were all greater for strong beats. However, end-systolic meridional stress (S:100 X 10(3) dynes/cm2; W:115 X 10(3) dynes/cm2) and end-systolic minor-axis dimension (S:4.75 cm; W:5.0 cm) were significantly greater for weak beats. Stress-length relations, derived from resting and postnitroglycerin determinations, revealed higher end-systolic dimensions for weak beats at any level of limiting afterload, suggesting diminished contractile performance of weak beats. Additionally, fractional minor-axis shortening for weak beats was diminished, at any level of end-systolic stress, in comparison with that for strong beats. The results are supportive of theories suggesting alternating contractile performance during pulsus alternans.