Renin-angiotensin-aldosterone system blockade in atrial fibrillation and left atrial remodelling

Abnormal vascular function in PR-interval prolongation

BACKGROUND

Underlying mechanisms of PR-interval prolongation leading to increased risk of adverse cardiovascular outcomes, including atrial fibrillation, are unclear. This study aims to investigate the relation between PR interval and changes in vascular function.

HYPOTHESIS

We hypothesize that there exists an intermediate pathological stage between electrocardiographic PR prolongation and adverse cardiovascular outcomes, which could be reflected by changes in surrogate measurements of vascular function.

METHODS

We recruited 88 healthy subjects (mean age 57.5 ± 9.8 y, 46% male) from a community-based health screening program who had no history of cardiovascular disease or diabetes mellitus. PR interval was determined from a resting 12-lead electrocardiogram. Vascular function was noninvasively assessed by flow-mediated dilation (FMD) using high-resolution ultrasound and brachial-ankle pulse wave velocity (PWV) using a vascular profiling system.

RESULTS

Only 3 subjects had a PR-interval length longer than the conventional cutoff of 200 ms. The PR-interval length was associated inversely with FMD (Pearson r = -0.30, P = 0.004) and positively with PWV (r = 0.40, P < 0.001). Adjusting for potential confounders, increased PR-interval length by each 25 ms was independently associated with reduced FMD by -1 unit (absolute %, B = -0.04 [95% confidence interval: -0.080 to -0.002, P = 0.040)] and increased PWV by +103 cm/second (B = +4.1 [95% confidence interval: 0.6-7.6, P = 0.023]).

CONCLUSIONS

This study shows that PR-interval length, even in the conventionally normal range, is independently associated with endothelial dysfunction and increased arterial stiffness in healthy subjects free of atherosclerotic disease. This suggests the presence of a systemic, intermediate pathologic stage of the vasculature in PR prolongation before clinically manifest cardiovascular events, and could represent a mediating mechanism.

Effects of selective mineralocorticoid receptor antagonism on atrial ion currents and early ionic tachycardia-induced electrical remodelling in rabbits

Over the past years, the importance of the renin-angiotensin-aldosterone system in atrial fibrillation (AF) pathophysiology has been recognised. Lately, the role of aldosterone in AF pathophysiology and mineralocorticoid receptor (MR) antagonism in "upstream" AF treatment is discussed. Hypothesising that selective MR antagonism might also influence atrial ion currents (L-type calcium current [I (Ca,L)], transient outward potassium current [I (to)], sustained outward potassium current [I (sus)]) and their tachycardia-induced remodelling, the effects of an eplerenone treatment were studied in a rabbit model. Six groups each with four animals were built. Animals of the control group received atrial pacing leads, but in contrast to the pacing groups, no atrial tachypacing (600 per minute for 24 and 120 h immediately before heart removal) was applied. Animals of the eplerenone groups were instrumented/paced as the corresponding control/pacing groups, but were additionally treated with eplerenone (7 days before heart removal). Atrial tachypacing was associated with a reduction of I (Ca,L). I (to) was decreased after 24 h of tachypacing, but returned to control values after 120 h. In the absence of rapid atrial pacing, MR antagonism reduced I (Ca,L) to a similar extent as 120 h of tachypacing alone. Based on this lower "take-off level", I (Ca,L) was not further decreased by high-rate pacing. I (to) and its expected tachycardia-induced alterations were not influenced by MR antagonism. In our experiments, selective MR antagonism influenced atrial I (Ca,L) and its tachycardia-induced alterations. As changes of I (Ca,L) are closely linked with atrial calcium signalling, the relevance of these alterations in AF pathophysiology and, accordingly, AF treatment is likely and has to be further evaluated.