Aims As atrial fibrillation is associated with significant mortality and morbidity, restoration of sinus rhythm is desirable. However, previous data suggest that cardioversion should be restricted to patients in whom the fibrillation is of limited duration (<1–2 years) because of high relapse rates. It may be the frequent association with cardiac disease, rather than the duration of fibrillation itself, which determined the high relapse of earlier studies. The aim of this study was to investigate rates of cardioversion, maintenance of sinus rhythm and predictors of subsequent relapse in a homogeneous group of patients without evidence of any co-existent cardiac disease.

Methods and Results We report on a retrospective series of 106 patients with thyrotoxicosis-induced fibrillation but no other heart disease: 87% had been in atrial fibrillation for >12 months (median duration 28·5, interquartile range 15–47 months). Cardioversion was attempted using disopyramide and then electric shock. Ninety-eight patients were successfully cardioverted: at late follow-up, 80·6±37 months (mean±SD), 67% were in sinus rhythm.

Conclusion Although a relationship between the duration of fibrillation and maintenance of sinus rhythm was found, the high proportion remaining in sinus rhythm, compared with other series, suggests this influence may be less important than the presence or absence of structural heart disease.

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Is there a place for the late cardioversion of atrial fibrillation?. A long-term follow-up study of patients with post-thyrotoxic atrial fibrillation

Background —The variation in stroke volume and pulse pressure characteristic of atrial fibrillation is usually ascribed to time-dependent ventricular filling, implying a single positive relationship between end-systolic pressure and volume, which defines a single state of myocardial contractility. We tested the hypothesis that contractility also varies.

Methods and Results —We measured the left ventricular pressure and volume continuously with a conductance catheter with catheter-tip micromanometer introduced retrogradely into the left ventricle. The end-systolic pressure-volume relationship was determined in 6 patients in atrial fibrillation undergoing cardiac catheterization for diagnostic purposes and 4 control patients in sinus rhythm undergoing coronary artery bypass graft surgery. The normal positive relationship between end-systolic pressure and volume was found in the control patients, but no such positive relationship was found in any patient in atrial fibrillation. In the latter, the slopes of the linear regressions were either not significantly different from zero or significantly negative ( r values <0.08), both results indicating a change in contractility from beat to beat. Significantly negative relationships were found between end-systolic volume and preceding R-R interval (−0.82< r <−0.24), indicating the presence of mechanical restitution. Significantly positive relationships were found between end-systolic volume and the R-R interval before the preceding R-R interval (0.35< r <0.74), indicating the presence of postextrasystolic potentiation.

Conclusions —Myocardial contractility is constantly changing from beat to beat in atrial fibrillation because of the influence of the force-interval relationships.

Myocardial Contractility Is Not Constant During Spontaneous Atrial Fibrillation in Patients

The clinical assessment of left ventricular (LV) systolic function during atrial fibrillation (AF) is unreliable and difficult because of beat-to-beat variability. We evaluated an index for the est...

https://www.physiology.org/doi/pdf/10.1152/ajpheart.2001.281.2.H573

Assessment of LV systolic function in atrial fibrillation using an index of preceding cardiac cycles

Left ventricular (LV) diastolic function during atrial fibrillation (AF) remains poorly understood due to the complex interaction of factors and beat-to-beat variability. The purpose of the present...

Determinants of LV diastolic function during atrial fibrillation: beat-to-beat analysis in acute dog experiments.

Cardiac impairment in atrial fibrillation is due both to loss of the atrial contribution to ventricular filling and to the adverse effects of an irregular rhythm compared with a regular rhythm These adverse effects are clinically most pronounced when ventricular rate is uncontrolled However, the mechanism of the adverse effect of a rapid ventricular rate with an irregular rhythm is not well understood In an observational study, we reported an increase in stroke volume variability with an increase in resting mean heart rate in atrial fibrillation Stroke volume variability, by decreasing cardiac efficiency, may contribute to impaired cardiac performance with tachycardia in atrial fibrillation The aim of this study is to describe how beat-to-beat variation in stroke volume changes with an increase in ventricular rate in atrial fibrillation Pulsed Doppler ultrasound was used to measure beat-by-beat stroke volumes and RR intervals before and after atropine, which increases heart rate without a direct inotropic effect

Ventricular rate and beat-to-beat variation of stroke volume in atrial fibrillation.

Objective : We tested the hypothesis that beat-to-beat changes in haemodynamics during atrial fibrillation include an effect of each preceding R–R interval through the interval–strength relationship (mechanical restitution). Background : The variation in stroke volume and pulse pressure characteristic of atrial fibrillation is usually ascribed to time dependent ventricular filling. Methods : We measured the maximum rate of rise of left ventricular pressure (LVd P /d t max), and aortic blood velocity and its integral in patients with atrial fibrillation undergoing cardiac catheterisation. The contractile response of isometric human myocardial trabeculae to sequences of atrial fibrillation was also studied, using the recorded ECGs as stimuli. The trabeculae were obtained from the resected right ventricular outflow tracts of patients with Fallot's tetralogy undergoing operative correction. Results : Beat-to-beat variations in contractile function during atrial fibrillation in the patients were recorded as LVd P /d t max and left ventricular ejection (ascending aortic) velocity integral (proportional to stroke volume). Both these indices correlated well with the response to the same ECG (R wave) sequences in the isometric model measured as the maximum rate of rise of force, d F /d t max, r =0.72 to 0.81, p <0.0001. When short pre-preceding intervals were excluded (minimizing the effect of post-extrasystolic potentiation), these variables showed a positive curvilinear relationship to preceding interval typical of mechanical restitution. Conclusions : Mechanical restitution, which causes beat-to-beat changes in inotropic state, accounts in part for the changes in stroke volume in atrial fibrillation.

Evidence for an influence of mechanical restitution on beat-to-beat variations in haemodynamics during chronic atrial fibrillation in patients

http://portlandpress.com/clinsci/article-pdf/80/s24/2P/830848/cs080002pd.pdf

T. Biggs

Papers

Evidence for an influence of mechanical restitution on beat-to-beat variations in haemodynamics during chronic atrial fibrillation in patients

Postextrasystolic Potentiation as a Cause of Beat to Beat Variation in Contractility during Atrial Fibrillation [AF]