Proarrhythmic Effects of Aldosterone During Myocardial Ischemia–Reperfusion: Implication of the Sarcolemmal-KATP Channels

Aldosterone Effect on Cardiac Structure and Function

BACKGROUND

Cardiac remodelling could be a key mechanism in aldosteronemediated cardiovascular morbidity and mortality. Experimental and clinical evidence has demonstrated that aldosterone causes cardiac structural remodelling and dysfunction by its profibrotic and pro-hypertrophic effects, which result mainly from the direct effects on myocardial collagen deposition, inflammation, and oxidative stress. Clinical studies have investigated the aldosterone effects on the heart in different clinical conditions, including general population, essential hypertension, primary aldosteronism, heart failure, and atrial fibrillation. Robust findings indicate that aldosterone or the activation of the cardiac mineralocorticoid receptor can cause damage to myocardial tissue by mechanisms independent of the blood pressure, leading to tissue hypertrophy, fibrosis, and dysfunction.

CONCLUSION

Aldosterone-mediated cardiovascular morbidity and mortality mainly result from cardiac structural and functional alterations. In different clinical settings, aldosterone can induce cardiac structural remodelling and dysfunction via several pathological mechanisms, including cardiac fibrosis, inflammation, and oxidative stress. Aldosterone antagonists could effectively decrease or reverse the detrimental aldosterone-mediated changes in the heart.

Spironolactone and perioperative atrial fibrillation occurrence in cardiac surgery patients: Rationale and design of the ALDOCURE trial

BACKGROUND

After artery bypass grafting (CABG), the presence of perioperative AF (POAF) is associated with greater short- and long-term cardiovascular morbidity. Underlying POAF mechanisms are complex and include the presence of an arrhythmogenic substrate, cardiac fibrosis and electrical remodeling. Aldosterone is a key component in this process. We hypothesize that perioperative mineralocorticoid receptor (MR) blockade may decrease the POAF incidence in patients with a left ventricular ejection fraction (LVEF) ≥50% who are referred for CABG with or without aortic valve replacement (AVR).

STUDY DESIGN

The ALDOCURE trial (NCT03551548) will be a multicenter, randomized, double-blind, placebo-controlled trial testing the superiority of a low-cost MR antagonist (MRA, spironolactone) on POAF in 1500 adults referred for on-pump elective CABG surgery with or without AVR, without any history of heart failure or atrial arrhythmia. The primary efficacy end point is the occurrence of POAF from randomization to within 5 days after surgery, assessed in a standardized manner. The main secondary efficacy end points include the following: postoperative AF occurring within 5 days after cardiac surgery, perioperative myocardial injury, major cardiovascular events and death occurring within 30 days of surgery, hospital and intensive care unit length of stay, need for readmission, LVEF at discharge and significant ventricular arrhythmias within 5 days after surgery. Safety end points, including blood pressure, serum potassium levels and renal function, will be monitored regularly throughout the trial duration.

CONCLUSION

The ALDOCURE trial will assess the effectiveness of spironolactone in addition to standard therapy for reducing POAF in patients undergoing CABG.

CLINICAL TRIAL REGISTRATION

NCT03551548.

PAR1 contribution in acute electrophysiological properties of oral anticoagulants in rabbit pulmonary vein sleeve preparations

Whether oral anticoagulants, vitamin K antagonists (VKAs), and nonvitamin K oral anticoagulant (NOACs) frequently prescribed to atrial fibrillation (AF) patients, do themselves have a pro- or anti-arrhythmic effect have never been addressed. Transmembrane action potentials were recorded in an acute rabbit model of superfused pulmonary veins (PVs) sleeves preparations using standard microelectrode technique. Fluindione 10 μm (n = 6) increased the AP (action potential) duration (APD), induced a significantly V_max depression (from 95 ± 14 to 53 ± 5 V/s, P < 0.05), and 2 : 1 blocks during rapid atrial pacing thus evoking class I anti-arrhythmic properties, and prevented spontaneous trigger APs. Apixaban 10 μm (n = 6) increased the APD, significantly prolonged the effective refractory period (from 56.3 ± 4.2 to 72.0 ± 8.6 ms, P < 0.05), and prevented triggered APs occurrence. Fluindione and apixaban effects were suppressed with the addition of the protease-activated receptors 1 (PAR 1) agonist SFLLR-NH₂ . Warfarin 10 μm (n = 6) significantly abbreviated the early refractory period (from 56.3 ± 4.2 to 45.0 ± 2.2 ms, P < 0.05) and increased triggered APs occurrence that were successfully prevented by nifedipine but not by the addition of the protease-activated receptors 1 agonist SFLLR-NH₂ . In this acute rabbit PVs model, VKAs and NOACs, at physiological concentrations, exhibited very different pharmacological properties that influence PVs electrophysiology, implying PAR1, with fluindione and apixaban which exhibited more anti-arrhythmic properties, whereas warfarin exhibited more pro-arrhythmic properties.

Preoperative plasma aldosterone and the risk of atrial fibrillation after coronary artery bypass surgery: a prospective cohort study

OBJECTIVE

Postoperative atrial fibrillation (POAF) is associated with poor outcomes after coronary artery bypass graft (CABG) surgery. We aimed to assess the additional value of preoperative plasma aldosterone levels, a biomarker promoting proarrhythmic and profibrotic pathways, for predicting POAF after CABG.

METHODS

We conducted a prospective cohort study involving consecutive patients with left ventricular ejection fraction (LVEF) more than 50% requiring elective CABG in our university hospital. Plasma aldosterone levels, two-dimensional echocardiography including left atrial strain analysis and galectin-3 (Gal-3) examination were assessed before cardiac surgery. The primary endpoint was the occurrence of POAF within 30 days after surgery.

RESULTS

POAF occurred in 34 (24.8%) out of the 137 included patients. Compared with controls, patients experiencing POAF were significantly older (73 years old ± 8 vs 65 ± 11, P < 0.001) and had higher preoperative plasma aldosterone levels [183 pmol/l (interquartile range 138-300) vs 143 pmol/l (interquartile range 96.5-216.5), P < 0.01]. Age [odds ratio (OR), 1.088; 95% confidence interval (CI) (1.038-1.140); P = 0.0004] and plasma aldosterone levels [OR, 1.007; 95% CI (1.003-1.012); P = 0.0013] were independently associated with POAF in multivariate analysis and could therefore be combined to predict the occurrence of POAF ['Aldoscore', OR, 2.7; 95% CI (1.7-4.3); P < 0.0001]. Reverse transcriptase PCR analysis performed on right atrial appendage and plasma examination revealed that Gal-3 was activated in POAF patients.

CONCLUSION

We developed the preoperative 'Aldoscore' for POAF risk stratification among patients with preserved LVEF requiring elective CABG. This new tool may be helpful to identify good responders to interventions targeting the proarrhythmic and profibrotic pathways of aldosterone.

Influence of steroid hormones on ventricular repolarization

QT interval prolongation, corrected for heart rate (QTc), either spontaneous or drug-induced, is associated with an increased risk of torsades de pointes and sudden death. Women have longer QTc than men and are at higher risk of torsades de pointes, particularly during post-partum and the follicular phase. Men with peripheral hypogonadism have longer QTc than healthy controls. The role of the main sex steroid hormones has been extensively studied with inconsistent findings. Overall, estradiol is considered to promote QTc lengthening while progesterone and testosterone shorten QTc. New findings suggest more complex regulation of QTc by sex steroid hormones involving gonadotropins (i.e. follicle-stimulating hormone), the relative concentrations of sex steroid hormones (which depends on gender, i.e., progesterone/estradiol ratio in women). Aldosterone, another structurally related steroid hormone, can also prolong ventricular repolarization in both sex. Better understanding of pathophysiological hormonal processes which may lead to increased susceptibility of women (and possibly hypogonadic men) to drug-induced arrhythmia may foster preventive treatments (e.g. progesterone in women). Exogenous hormonal intake might offer new therapeutic opportunities or, alternatively, increase the risk of torsades de pointes. Some exogenous sex steroids may also have paradoxical effects on ventricular repolarization. Lastly, variations of QTc in women linked to the menstrual cycle and sex hormone fluctuations are generally ignored in regulatory thorough QT studies. Investigators and regulatory agencies promoting inclusion of women in thorough QT studies should be aware of this source of variability especially when studying drugs over several days of administration.

Rapid and MR-Independent IK1 Activation by Aldosterone during Ischemia-Reperfusion

In ST elevation myocardial infarction (STEMI) context, clinical studies have shown the deleterious effect of high aldosterone levels on ventricular arrhythmia occurrence and cardiac mortality. Previous in vitro reports showed that during ischemia-reperfusion, aldosterone modulates K⁺ currents involved in the holding of the resting membrane potential (RMP). The aim of this study was to assess the electrophysiological impact of aldosterone on I_K1 current during myocardial ischemia-reperfusion. We used an in vitro model of “border zone” using right rabbit ventricle and standard microelectrode technique followed by cell-attached recordings from freshly isolated rabbit ventricular cardiomyocytes. In microelectrode experiments, aldosterone (10 and 100 nmol/L, n=7 respectively) increased the action potential duration (APD) dispersion at 90% between ischemic and normoxic zones (from 95±4 ms to 116±6 ms and 127±5 ms respectively, P<0.05) and reperfusion-induced sustained premature ventricular contractions occurrence (from 2/12 to 5/7 preparations, P<0.05). Conversely, potassium canrenoate 100 nmol/L and RU 28318 1 μmol/l alone did not affect AP parameters and premature ventricular contractions occurrence (except Vmax which was decreased by potassium canrenoate during simulated-ischemia). Furthermore, aldosterone induced a RMP hyperpolarization, evoking an implication of a K⁺ current involved in the holding of the RMP. Cell-attached recordings showed that aldosterone 10 nmol/L quickly activated (within 6.2±0.4 min) a 30 pS K⁺-selective current, inward rectifier, with pharmacological and biophysical properties consistent with the I_K1 current (NPo =1.9±0.4 in control vs NPo=3.0±0.4, n=10, P<0.05). These deleterious effects persisted in presence of RU 28318, a specific MR antagonist, and were successfully prevented by potassium canrenoate, a non specific MR antagonist, in both microelectrode and patch-clamp recordings, thus indicating a MR-independent I_K1 activation. In this ischemia-reperfusion context, aldosterone induced rapid and MR-independent deleterious effects including an arrhythmia substrate (increased APD₉₀ dispersion) and triggered activities (increased premature ventricular contractions occurrence on reperfusion) possibly related to direct I_K1 activation.

Role of mineralocorticoid receptor antagonists in cardiovascular disease

Aldosterone exerts its best known sodium homeostasis actions by controlling sodium excretion at the level of the distal tubules via activation of the apical epithelial sodium channel and the basolateral Na(+)/K(+)ATPase pump. Recently, this mineralocorticoid hormone has been demonstrated to act on the heart and blood vessels. Excess release of aldosterone in relation to the salt status induces both genomic and nongenomic effects that by promoting endothelial dysfunction, and vascular and cardiorenal adverse remodeling, contribute to the target organ damage found in hypertension, heart failure, myocardial infarction, and chronic renal failure. Mineralocorticoid receptor blockers have been shown to be highly effective in resistant hypertension and to slow down heart failure progression, and in experimental animals, the development of atherosclerosis. Blockade of the action of aldosterone and potentially other mineralocorticoid steroids has been increasingly demonstrated to be an extremely beneficial therapy in different forms of cardiovascular disease. This review provides a summary of the knowledge that exists on aldosterone actions in the cardiovascular system and, in providing the translational impact of this knowledge to the clinical arena, illustrates how much more needs to be achieved in exploring the use of mineralocorticoid receptor blockers in less advanced stages of heart, renal, and vascular disease.

Electrophysiological and antiarrhythmic properties of potassium canrenoate during myocardial ischemia-reperfusion

INTRODUCTION

Recent clinical studies have reported the potential benefit of an early mineralocorticoid receptor (MR) blockade with potassium canrenoate (PC) on ventricular arrhythmias (VAs) occurrence in patients experiencing an ST-segment elevation myocardial infarction (STEMI). However, most of the electrophysiological properties of PC demonstrated to date have been investigated in normoxic conditions, and therefore, in vitro experiments during an acute myocardial ischemia-reperfusion were lacking.

MATERIALS AND METHODS

We used rabbit in vitro models and standard microelectrode technique to assess the electrophysiological impact of PC during myocardial ischemia-reperfusion, including right ventricle mimicking the "border zone" existing between normal and ischemic/reperfused areas (1 µmol/L, 10 and 100 nmol/L), isolated right ventricle, and sinoatrial node (SAN) experiments (1 µmol/L, respectively).

RESULTS

During ischemia-reperfusion, acute superfusion of PC 100 nmol/L prevented the increase in action potential (AP) duration at 90% of repolarization (APD90) dispersion between ischemic and nonischemic areas and in VAs occurrence induced by aldosterone 10 nmol/L (86 ± 3 vs 114 ± 4 milliseconds for aldosterone alone, P < .05). Potassium canrenoate also induced conduction blocks and significantly decreased Vmax during simulated ischemia (from 25 ± 5 to 12 ± 4, 14 ± 3, and 14 ± 5 V/s, respectively, for PC 1 µmol/L, 100, and 10 nmol/L, P < .05). Potassium canrenoate 1 µmol/L demonstrated cycle length (CL)-dependent effects on APD90 and on Vmax, and it also reduced SAN beating CL (from 446 ± 28 to 529 ± 24 millisecond, P < .05).

CONCLUSION

Our experimental study highlights new evidence for an antiarrhythmic impact of PC during myocardial ischemia-reperfusion via multiple channels modulation. These results are in line with recent clinical trials suggesting that an early MR blockade in STEMI may be preventive of VAs.