Interval-force relation is unaffected by the presence of cardiomyopathy orcoronary artery disease in patients with atrial fibrillation

Background: We tested the hypothesis that cycle length-dependent cardiac co ntractility in atrial fibrillation is primarily governed by the negative in terval-force relation in patients with normal and depressed systolic functi on. Methods and Results: We performed two-dimensional guided M-mode echocardiog raphy in 41 patients (mean age, 69 +/- 4 years; range, 48 to 92 years; 19 m en, 11 women). Twelve patients had objective evidence of left ventricular s ystolic dysfunction (CMP; mean ejection fraction, 37% +/- 7%) in the absenc e of coronary artery disease (CAD), 13 patients had documented CAD (mean ej ection fraction, 43% +/- 6%), and 16 patients had normal resting left ventr icular systolic function (mean ejection fraction, 58% +/- 7%). Simultaneous beat-to-beat blood pressure, end-systolic and end-diastolic dimension, cir cumferential velocity of fiber shortening (Vcf), and end-systolic wall stre ss (ESWS) were calculated for all patients. All three groups showed a signi ficant linear relation between beat-to-beat Vcf and Vcf corrected for after load (represented as the Vcf/ESWS ratio) and preceding cycle length. There was, however, no significant difference in the relation between either of t hese variables and cycle length among the three groups. There was also no d ifference in the rate of change in either Vcf or Vcf corrected for afterloa d (Vcf/ESWS ratio) from beat-to-beat among the three groups. Control patien ts with normal systolic function showed greater Vcf at any given cycle leng th compared with patients with CMP or CAD. Conclusion: Our data show that, for each beat in atrial fibrillation, Vcf a nd Vcf/ESWS ratio are decreased after shorter cycle lengths and increased a fter long cycles, but there is no significant attenuation of this effect in patients with systolic dysfunction with or without coronary disease compar ed with controls. Thus, the negative interval-force relation, the predomina nt determinant of beat-to-beat variation in contractility in atrial fibrill ation, is preserved in patients with CAD or reduced left ventricular systol ic function.