Intravenous Canrenone in Paroxysmal Atrial Fibrillation: A Reappraisal of Clinical Utility

To the Editor,

I read with interest the pilot randomized, double-blind study by Dąbrowski et al ¹ evaluating intravenous canrenone for sinus rhythm (SR) restoration in patients with paroxysmal atrial fibrillation (AF). In this trial, 52 patients with recent-onset AF were randomized to receive either intravenous canrenone or placebo, with the primary endpoint being SR restoration within a 2-h observation period. The study was discontinued early following an interim futility analysis, as no statistically significant difference in conversion rates was observed between groups. The authors should be commended for exploring a novel therapeutic angle by targeting aldosterone-mediated pathways during acute AF episodes. Nevertheless, certain aspects merit further consideration before canrenone is dismissed in this context.

The absolute difference in SR restoration between canrenone (16.0%) and placebo (11.5%) was modest and statistically nonsignificant. However, given the small sample size and lower-than-expected conversion rates, the study may not have been sufficiently powered to detect clinically relevant but subtle effects. The anticipated 50% SR restoration rate in the treatment arm may have overestimated canrenone's short-term efficacy, particularly considering its pharmacodynamic profile.

A central point of discussion lies in the chosen 2-h observation window. Mineralocorticoid receptor antagonists (MRAs) such as canrenone are not conventional acute antiarrhythmics. Their benefits in AF are thought to arise through upstream mechanisms, including modulation of atrial remodeling, attenuation of fibrosis, and neurohormonal regulation—processes that evolve over time rather than within hours.^2,3 Therefore, evaluating canrenone exclusively for rapid cardioversion may underestimate its therapeutic potential in longer-term rhythm control strategies.

In addition, variability in background therapies may have influenced outcomes. Patients were permitted to receive agents such as β-blockers, amiodarone, or propafenone prior to or during the observation period. These medications exert independent electrophysiological effects that may confound or obscure the isolated impact of canrenone. Future trials might consider stratified randomization or stricter control of concomitant pharmacotherapy to better delineate treatment effects.

Another important consideration is the absence of serum aldosterone or renin–angiotensin–aldosterone system biomarker measurements. Given that the study's rationale centered on aldosterone's arrhythmogenic role, assessment of neurohormonal activation before and after intervention would have provided valuable mechanistic insight. Evidence suggests that elevated aldosterone levels correlate with AF burden and that MRA therapy reduces the risk of AF development and recurrence. A recent meta-analysis published in the American Journal of Cardiology demonstrated that MRAs reduce the risk of AF by 23% compared with control therapy, with consistent effects in both new-onset and recurrent AF. ⁴ Such findings support further exploration of MRAs in AF management, particularly in patients with demonstrable neurohormonal activation.

Importantly, canrenone demonstrated excellent tolerability, with no significant adverse effects reported in the treatment arm. This favorable safety profile is reassuring and may support its evaluation in broader clinical contexts—especially if future studies can better define optimal timing, dosing strategies, and patient subgroups most likely to benefit.

In conclusion, although the present findings do not support intravenous canrenone as a stand-alone agent for acute pharmacologic cardioversion, they should not preclude further investigation. Its upstream properties and favorable safety profile warrant assessment in larger, adequately powered trials focusing on AF recurrence prevention or combination therapeutic strategies.