13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

RT-238

Heart failure patients with atrial fibrillation: how important is it to regularise ventricular rhythm?

Panos E. Vardas, Emmanuel N. Simantirakis, Emmanuel G. Manios.
Cardiology Department, University Hospital of Heraklion, Crete, Greece

Experimental and clinical studies

Although the negative effect of an irregular ventricular rhythm on cardiac performance was proved long ago, mainly by experimental animal studies³ but also by clinical studies in humans^1,2, only recently has been any investigation into the effects of regularisation of the ventricular rhythm on ventricular function and the patient's quality of life. In 1993 Naito et al³ reported their findings concerning the effects of an abnormal ventricular rhythm on cardiac output in dogs with complete atrioventricular block. They found that ventricular pacing which caused an abnormal ventricular rhythm led to a 9% reduction in cardiac output, compared with ventricular pacing at the same rate but with equal R-R intervals. Moreover, they demonstrated angiographically that mitral regurgitation appeared during pacing with the irregular rhythm but disappeared during pacing with regular beat to beat intervals. Daoud et al⁵ were the first to examine the haemodynamic effect of regular and irregular ventricular pacing at identical average heart rates in patients with atrial fibrillation and complete atrioventricular block. After radiofrequency ablation of the atrioventricular junction they measured the cardiac output (Fick method), pulmonary artery pressure and wedge pressure during regular and irregular ventricular pacing from the right ventricular apex with the same mean pacing rate. They found that at mean cycle lengths of both 750 ms (80 bpm) and 500 ms (120 bpm) irregular pacing caused a 12% reduction in cardiac output. The results of this study suggest that an irregular ventricular rhythm, independently of rate, has deleterious effects on myocardial function. Natale et al⁴, in a recent prospective study, examined the impact on ventricular function and quality of life of atrioventricular nodal ablation in chronic atrial fibrillation with a normal ventricular response. They concluded that a chronic irregular heart rate alone could produce an overall reduction in cardiac function that can be reversed by atrioventricular nodal ablation and pacemaker implantation. This procedure could represent a more appropriate therapeutic modality over treatments targeting rate control, particularly in patients with left ventricular dysfunction. In a recent presentation by Natale et al at the 1997 ACC meeting⁶ the authors reported that, in patients with chronic atrial fibrillation, discontinuation of "effective" therapy for rate control (b-blockers, Ca⁺⁺ antagonists, digoxin) followed by atrioventricular nodal ablation and pacing seems to improve the quality of life and symptom severity, as well as left ventricular function. In this study the authors did not find any difference between the exercise duration and VO₂ max before and after ablation.

The results from a recent study (still in progress) in our own department confirm the findings of the above investigators, while also establishing the importance of the restoration of the patients' chronotropy during exercise. This study so far involves 14 patients, aged 72 ± 6 years, with NYHA Class II or III heart failure and chronic atrial fibrillation with resting heart rate between 60 and 100 bpm. The patients were taking no antiarrhythmic medication apart from digitalis. All patients underwent radiofrequency catheter ablation of the atrioventricular junction and implantation of a permanent VVIR pacemaker. One day before and one and six months after the ablation ejection fraction was measured echocardiographically and a symptom limited exercise test (Naughton) with breath-by-breath gas exchange analysis was carried out to determine oxygen consumption at peak exercise and at the anaerobic threshold. The importance of the procedure to the patients' quality of life was evaluated using a special questionnaire. We found that ejection fraction increased significantly, from 34 ± 8% before to 41 ± 9% six months after the procedure (p < 0.01). The ergospirometric parameters also improved after the atrioventricular junctional ablation. Oxygen consumption showed a trend to increase from 15.4 ± 0.8 to 17.8 ± 0.6 ml/kg/min (p = 0.06) at peak exercise and from 12.1 ± 0.6 to 14.8 ± 1 ml/kg/min (p = 0.06) at the aerobic threshold. According to the questionnaires there was a significant improvement in quality of life and a decrease in the severity of symptoms.

It should be noted that our findings regarding the improvement in the patients' exercise performance differ from those of Natale et al. However, it is not clear whether the patient populations in the two studies are comparable: further studies with larger numbers of patients are needed to clarify this matter.

Although the precise underlying mechanism for the reduction in cardiac output associated with an irregular rhythm has not been well established various mechanisms have been implicated. The beat-to-beat variation in ventricular filling which results from an irregular rhythm influences the intensity of cardiac systole via the Frank-Starling mechanism and the interval-force relation¹². Neurohormonal and vasculokinetic changes¹³, as well as inefficient ventricular mechanics² may also cause a reduction in cardiac output. Lastly, mitral regurgitation caused by the irregular rhythm may contribute to the adverse haemodynamics³.