What is the clinical evidence from this study?

Study design: Observational. Population: Patients in sinus rhythm undergoing cardiac surgery (n=212). Intervention: Beta-blocker therapy vs. No beta-blocker therapy. Primary outcome: Incidence of post-cardiac surgery atrial fibrillation (p=0.038).

August 22, 2006

Post‐Operative Atrial Fibrillation Is Influenced by Beta‐Blocker Therapy But Not by Pre‐Operative Atrial Cellular Electrophysiology

Key Result

Chronic pre-operative beta-blocker therapy reduced the incidence of post-cardiac surgery atrial fibrillation from 27% to 13% (P=0.038), independent of pre-operative atrial effective refractory period.

Study Design

Type

Observational (n=212)

Multicenter

Structured PICO

Does pre-operative atrial cellular electrophysiology predict, and does beta-blocker therapy reduce, new-onset atrial fibrillation in patients undergoing cardiac surgery?

Population

212 consenting patients in sinus rhythm undergoing cardiac surgery between 1999 and 2005, from whom right atrial appendage tissue was obtained.

Intervention

Pre-operative chronic beta-blocker therapy (>7 days) and ex vivo atrial cellular electrophysiology assessment.

Comparator

Patients not receiving pre-operative beta-blocker therapy, and patients who did not develop post-operative atrial fibrillation.

Outcome

Incidence of new-onset post-cardiac surgery atrial fibrillation (AF) within 7 days.

Pre-operative atrial cellular electrophysiology does not predict post-operative atrial fibrillation, but chronic beta-blocker therapy reduces its incidence independently of pre-operative effective refractory period prolongation.

Main Result

Absolute Event Rate: 13% vs 27%

p-value: p=0.038

Limitations

Retrospective analysis of clinical data
Measurement of ERP in isolated cells has limitations compared to in-vivo measurements and does not inform about conduction or spatial heterogeneity
Cell isolation technique has recognized limitations including potential disruption of ion currents and relatively low yield and depolarization of myocytes
Atrial structure was not examined in the study

Abstract

INTRODUCTION: We investigated whether post-cardiac surgery (CS) new-onset atrial fibrillation (AF) is predicted by pre-CS atrial cellular electrophysiology, and whether the antiarrhythmic effect of beta-blocker therapy may involve pre-CS pharmacological remodeling. METHODS AND RESULTS: Atrial myocytes were obtained from consenting patients in sinus rhythm, just prior to CS. Action potentials and ion currents were recorded using whole-cell patch-clamp technique. Post-CS AF occurred in 53 of 212 patients (25%). Those with post-CS AF were older than those without (67 +/- 2 vs 62 +/- 1 years, P = 0.005). In cells from patients with post-CS AF, the action potential duration at 50% and 90% repolarization, maximum upstroke velocity, and effective refractory period (ERP) were 13 +/- 4 ms, 217 +/- 16 ms, 185 +/- 10 V/s, and 216 +/- 14 ms, respectively (n = 30 cells, 11 patients). Peak L-type Ca(2+) current, transient outward and inward rectifier K(+) currents, and the sustained outward current were -5.0 +/- 0.5, 12.9 +/- 2.4, -4.1 +/- 0.4, and 9.7 +/- 1.0 pA/pF, respectively (13-62 cells, 7-19 patients). None of these values were significantly different in cells from patients without post-CS AF (P > 0.05 for each, 60-279 cells, 29-86 patients), confirmed by multiple and logistic regression. In patients treated >7 days with a beta-blocker pre-CS, the incidence of post-CS AF was lower than in non-beta-blocked patients (13% vs 27%, P = 0.038). Pre-CS beta-blockade was associated with a prolonged pre-CS atrial cellular ERP (P = 0.001), by a similar degree (approximately 20%) in those with and without post-CS AF. CONCLUSION: Pre-CS human atrial cellular electrophysiology does not predict post-CS AF. Chronic beta-blocker therapy is associated with a reduced incidence of post-CS AF, unrelated to a pre-CS ERP-prolonging effect of this treatment.

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