Mechanics of pulsus alternans in aortic valve stenosis

Abstract

Abstract Differences in the mechanics of strong and weak contractions during sustained pulsus atternans 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 × 10 3 dynes/cm 2 ; W:205 × 10 3 dynes/cm 2 ), the time integral of left ventricular (LV) meridional systolic stress (S:5,000 × 10 3 dynes/cm 2 ; W:4,500 × 10 3 dynes/cm 2 ) and the area of a stress dimension loop (S:202 × 10 3 dyne/cm; W 165 × 10 3 dyne/cm) were all greater for strong beats. However, end-systolic meridional stress (S: 100 × 10 3 dynes/cm 2 ; W:115 × 10 3 dynes/cm 2 ) 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.