Myocardial relaxation in atrial fibrillation.

Although myocardial contractility has been known to vary from beat to beat in atrial fibrillation, myocardial relaxation in this arrhythmia has not been investigated. In this study, left ventricular relaxation was examined in seven patients with atrial fibrillation (four with mitral valve disease, one with aortic regurgitation, one with secundum type atrial septal defect and one with apical left ventricular hypertrophy). The left ventricular pressure was measured with a micromanometer-tipped catheter and the time constant of isovolumic left ventricular pressure decline (the relaxation time constant) was calculated by means of exponential curve fitting from more than 20 consecutive beats in each patient. The maximal rate of rise of left ventricular pressure (dP/dt) and the relaxation time constant were examined in relation to the preceding RR interval (RR2) and to the ratio of the RR2 interval to the pre-preceding RR interval (RR2/RR1), and the correlation coefficients were obtained. The dP/dt correlated better with RR2/RR1 than with the RR2 interval (0.82 +/- 0.05 versus 0.48 +/- 0.2), but the relaxation time constant did not show any correlation with RR2/RR1 or the RR2 interval (0.03 +/- 0.21 and 0.06 +/- 0.21, respectively). The relaxation time constant was fairly constant in each patient even when the RR2 interval and RR2/RR1 varied greatly. Thus, relaxation in atrial fibrillation is independent of changes in contractility as seen in the relation between postextrasystolic relaxation and postextrasystolic potentiation of contractility.

[1]  D. Adam,et al.  Myocardial Relaxation. V. Postextrasystolic Contraction‐Relaxation in the Intact Dog Heart , 1981, Circulation.

[2]  E. Braunwald,et al.  STUDIES ON STARLING'S LAW OF THE HEART. III. OBSERVATIONS IN PATIENTS WITH MITRAL STENOSIS AND ATRIAL FIBRILLATION ON THE RELATIONSHIPS BETWEEN LEFT VENTRICULAR END-DIASTOLIC SEGMENT LENGTH, FILLING PRESSURE, AND THE CHARACTERISTICS OF VENTRICULAR CONTRACTION. , 1960, The Journal of clinical investigation.

[3]  Y. Nakamura,et al.  Responses of peak ear-pulse derivative to changing left ventricular function. , 1980, The American journal of physiology.

[4]  F. R. Ruckdeschel.  Basic Scientific Subroutines, Volume II. , 1981 .

[5]  W. Parmley,et al.  Relation between mechanics of contraction and relaxation in mammalian cardiac muscle. , 1969, The American journal of physiology.

[6]  J. Ross,et al.  Effects of changes in preload, afterload and inotropic state on ejection and isovolumic phase measures of contractility in the conscious dog. , 1975, The American journal of cardiology.

[7]  J. Weiss,et al.  Hemodynamic determinants of the time-course of fall in canine left ventricular pressure. , 1976, The Journal of clinical investigation.

[8]  C Fisch,et al.  The role of inotropic variation in ventricular function during atrial fibrillation. , 1970, The Journal of clinical investigation.

[9]  M. Noble,et al.  The Contractile State of Cat and Dog Heart in Relation to the Interval between Beats , 1980, Circulation research.

[10]  M. Morad,et al.  Excitation-contraction coupling in heart muscle: Membrane control of development of tension , 1973 .

[11]  J. Carroll,et al.  Left ventricular isovolumic pressure decay and diastolic mechanics after postextrasystolic potentiation and during exercise. , 1983, The American journal of cardiology.

[12]  B. Wohlfart.  Relationships between peak force, action potential duration and stimulus interval in rabbit myocardium. , 1979, Acta physiologica Scandinavica.

[13]  J. Gault,et al.  Factors influencing the ejection fraction and the mean rate of circumferential fibre shortening during atrial fibrillation in man. , 1974, Cardiovascular research.

[14]  R. W. Brower,et al.  Interaction of left ventricular relaxation and filling during early diastole in human subjects. , 1980, The American journal of cardiology.

[15]  M. Noble,et al.  The action‐potential duration and contractile response of the intact heart related to the preceding interval and the preceding beat in the dog and cat , 1981, The Journal of physiology.

[16]  R. O'rourke,et al.  Pharmacologic and hemodynamic influences on the rate of isovolumic left ventricular relaxation in the normal conscious dog. , 1977, The Journal of clinical investigation.

[17]  K. Peterson,et al.  Left ventricular function in chronic constrictive pericarditis. , 1974, The American journal of cardiology.

[18]  Y. Hirota,et al.  Sequential changes of left ventricular function after cineangiography in normal heart and coronary artery disease. , 1984, Japanese circulation journal.

[19]  D. Severson,et al.  Cyclic nucleotides and cardiac function. , 1979, Circulation research.

[20]  N. Dhalla,et al.  Subcellular basis of cardiac contractile failure. , 1978, Journal of molecular and cellular cardiology.

[21]  M. Noble,et al.  The relationship between the strength of the human heart beat and the interval between beats. , 1982, Circulation.

[22]  H. Dodge,et al.  Ventricular Dynamics in Atrial Fibrillation , 1957, Circulation.