Atrial fibrillation : clinical managements with special emphasis on cardioversion

Atrial fibrillation (AF) is the most common arrhythmia of clinical importance. It often decreases quality of life and is related to significant morbidity, as well as decreases longevity. This thesis covers three main issues of importance in the management of patients with AF: · Knowledge of and adherence to published guidelines; · Symptomatology of paroxysmal and persistent AF; · Aspects of electrical cardioversion of AF.

Knowledge of and proneness to adhere to Swedish guidelines were studied by asking 728 physicians to respond to a questionnaire focusing on relevant issues when handling patients with AF. In parallel, 200 records from patients hospitalized for AF were reviewed to verify actual compliance to the guidelines. Only 40% of the patients with persistent AF and risk factors for stroke, received warfarin, although they did not have any contraindication to such treatment. Several discrepancies were detected, regarding the prescription of antiarrhythmic therapy. In conclusion, there was a lack of compliance between management as recommended by the guidelines and actual practice concerning several important aspects, some of which exposed patients to unnecessary risk.

A structured medical history, two-dimensional echocardiography and 24-h Holter-ECG were obtained from 282 consecutive patients with persistent AF in order to investigate the differences between patients with and without symptoms and the prevalence of left ventricular dysfunction. Apart from the presence of valvular heart disease, symptomatic and asymptomatic subjects did not differ. Approximately 20% in this group had an impaired left ventricular function, this was more prevalent among those with high ventricular rate, ischemic heart disease and male gender.

Episodes of paroxysmal AF are often asymptomatic. It is not known whether such episodes differ from symptomatic episodes. In a group of twenty-one patients with an implanted atrial def ibrillator, symptomatic episodes that caused the patient to attend hospital for cardioversion were compared with episodes that did not lead the patient to a hospital visit. Episodes ending with cardioversion were characterized by a high initial ventricular rate and longer duration than those that were unnoted.

To test the hypotheses that one high-energy shock is more efficacious than incremental shocks, 120 consecutive patients referred for a first elective cardioversion were randomized to one shock of 360 J or incremental shocks starting at 100 J with a stepwise increase to 360 J. There were no differences in efficacy, sinus rhythm being obtained in 87 and 91 % in the two groups respectively. One single shock of 360 J caused less chest discomfort than the strategy based on incremental energy shocks. Neither of the two groups revealed any signs of myocardial injury.

There are theoretical reasons to believe that rapid atrial pacing prior to the delivery of a cardioversion shock may lower the atrial defibrillation threshold (ADFT). This hypothesis was tested in 11 patients by pre-shock atrial pacing during internal cardioversion of AF. The ADFT was recorded in a randomized design, applying a step-up protocol starting at 100 V At each energy level the shock preceded by pacing was compared to a shock given without pacing until a level when sinus rhythm was restored by either of the two modes. Subsequently the step-up protocol was repeated applying the inverse sequence of the modes. The hypothesis could not be confirmed since rapid atrial pacing, did not influence the internal ADFT, at least not according to the protocol used.

In conclusion, AF is associated with an increased morbidity and mortality. Through careful patient management the risks can be minimized and the need for medical care reduced. The described studies increase the understanding of the symptomatology and electrophysiological mechanisms and may hopefully contribute to improve patient care in this large group of people.

List of scientific papers

I. Frykman V, Beerman B, Ryden L, Rosenqvist M (2001). Management of atrial fibrillation: discrepancy between guideline recommendations and actual practice exposes patients to risk for complications. Eur Heart J. 22(20): 1954-9.
https://pubmed.ncbi.nlm.nih.gov/11601840

II. Frykman V, Frick M, Jensen-Urstad M, Ostergren J, Rosenqvist M (2001). Asymptomatic versus symptomatic persistent atrial fibrillation: clinical and noninvasive characteristics. J Intern Med. 250(5): 390-7.
https://pubmed.ncbi.nlm.nih.gov/11887973

III. Frykman V, Ayers G, Darpo B, Rosenqvist M (2002). What characterizes episodes of symtomatic fibrillation requiring cardioversion? Experiences from patients with an implantable atrial cardioverter. Am Heart J.

IV. Frykman V, Ryden L, Rosenqvist M (2002). Energy requirements for elective external cardioversion of persistent atrial fibrillation. A study f efficacy and safety. [Submitted]

V. Frykman V, Darpo B, Ayers G, Bergfeldt L, Linde C, Rosenqvist M (2002). Rapid atrial pacing does not decrease the atrial defibrillation threshold. [Submitted]