Diadenosine-5-phosphate exerts A1-receptor-mediated proarrhythmic effects in rabbit atrial myocardium

Coffee Consumption and Incident Tachyarrhythmias: Reported Behavior, Mendelian Randomization, and Their Interactions

Importance

The notion that caffeine increases the risk of cardiac arrhythmias is common. However, evidence that the consumption of caffeinated products increases the risk of arrhythmias remains poorly substantiated.

Objective

To assess the association between consumption of common caffeinated products and the risk of arrhythmias.

Design, Setting, and Participants

This prospective cohort study analyzed longitudinal data from the UK Biobank between January 1, 2006, and December 31, 2018. After exclusion criteria were applied, 386 258 individuals were available for analyses.

Exposures

Daily coffee intake and genetic polymorphisms that affect caffeine metabolism.

Main Outcomes and Measures

Any cardiac arrhythmia, including atrial fibrillation or flutter, supraventricular tachycardia, ventricular tachycardia, premature atrial complexes, and premature ventricular complexes.

Results

A total of 386 258 individuals (mean [SD] age, 56 [8] years; 52.3% female) were assessed. During a mean (SD) follow-up of 4.5 (3.1) years, 16 979 participants developed an incident arrhythmia. After adjustment for demographic characteristics, comorbid conditions, and lifestyle habits, each additional cup of habitual coffee consumed was associated with a 3% lower risk of incident arrhythmia (hazard ratio [HR], 0.97; 95% CI, 0.96-0.98; P < .001). In analyses of each arrhythmia alone, statistically significant associations exhibiting a similar magnitude were observed for atrial fibrillation and/or flutter (HR, 0.97; 95% CI, 0.96-0.98; P < .001) and supraventricular tachycardia (HR, 0.96; 95% CI, 0.94-0.99; P = .002). Two distinct interaction analyses, one using a caffeine metabolism-related polygenic score of 7 genetic polymorphisms and another restricted to CYP1A2 rs762551 alone, did not reveal any evidence of effect modification. A mendelian randomization study that used these same genetic variants revealed no significant association between underlying propensities to differing caffeine metabolism and the risk of incident arrhythmia.

Conclusions and Relevance

In this prospective cohort study, greater amounts of habitual coffee consumption were associated with a lower risk of arrhythmia, with no evidence that genetically mediated caffeine metabolism affected that association. Mendelian randomization failed to provide evidence that caffeine consumption was associated with arrhythmias.

Impact of Lifestyle Modification on Atrial Fibrillation

Atrial Fibrillation (AF) is the most common arrhythmia in adults, and the rapid increase in AF prevalence has been classified by experts as an epidemic. The mechanisms of AF are complex and incompletely understood. While many aspects of management are now based on high quality evidence, other clinical decisions are based on experience and judgment. This article provides an up to date review relating to lifestyle modification and its effect on AF to inform clinical treatment. This comprehensive review used PubMed and Google Scholar to perform keyword searches of articles published between 1998 and the present, with the exception of the 1978 "Holiday Heart" article. Robust data has emerged identifying multiple risk factors for development of AF, including age, sex, hypertension, diabetes mellitus, obesity, alcohol consumption, exercise, and obstructive sleep apnea. Recent evidence indicates that lifestyle modification has a significant role in mitigating the risk and burden of AF. In conclusion, based on the available evidence, an interdisciplinary approach to lifestyle modification will likely reduce risk and/or symptom burden of AF.

Diadenosine pentaphosphate affects electrical activity in guinea pig atrium via activation of potassium acetylcholine-dependent inward rectifier

Diadenosine pentaphosphate (Ap5A) belongs to the family of diadenosine polyphosphates, endogenously produced compounds that affect vascular tone and cardiac performance when released from platelets. The previous findings indicate that Ap5A shortens action potentials (APs) in rat myocardium via activation of purine P2 receptors. The present study demonstrates alternative mechanism of Ap5A electrophysiological effects found in guinea pig myocardium. Ap5A (10-4 M) shortens APs in guinea pig working atrial myocardium and slows down pacemaker activity in the sinoatrial node. P1 receptors antagonist DPCPX (10-7 M) or selective GIRK channels blocker tertiapin (10-6 M) completely abolished all Ap5A effects, while P2 blocker PPADS (10-4 M) was ineffective. Patch-clamp experiments revealed potassium inward rectifier current activated by Ap5A in guinea pig atrial myocytes. The current was abolished by DPCPX or tertiapin and therefore was considered as potassium acetylcholine-dependent inward rectifier (I KACh). Thus, unlike rat, in guinea pig atrium Ap5A produces activation of P1 receptors and subsequent opening of KACh channels leading to negative effects on cardiac electrical activity.

Diadenosine tetra- and pentaphosphates affect contractility and bioelectrical activity in the rat heart via P2 purinergic receptors

Diadenosine polyphosphates (Ap(n)As) are endogenously produced molecules which have been identified in various tissues of mammalian organism, including myocardium. Ap(n)As contribute to the blood clotting and are also widely accepted as regulators of blood vascular tone. Physiological role of Ap(n)As in cardiac muscle has not been completely elucidated. The present study aimed to investigate the effects of diadenosine tetra- (Ap4A) and penta- (Ap5A) polyphosphates on contractile function and action potential (AP) waveform in rat supraventricular and ventricular myocardium. We have also demonstrated the effects of A4pA and Ap5A in myocardial sleeves of pulmonary veins (PVs), which play a crucial role in genesis of atrial fibrillation. APs were recorded with glass microelectrodes in multicellular myocardial preparations. Contractile activity was measured in isolated Langendorff-perfused rat hearts. Both Ap4A and Ap5A significantly reduced contractility of isolated Langendorff-perfused heart and produced significant reduction of AP duration in left and right auricle, interatrial septum, and especially in right ventricular wall myocardium. Ap(n)As also shortened APs in rat pulmonary veins and therefore may be considered as potential proarrhythmic factors. Cardiotropic effects of Ap4A and Ap5A were strongly antagonized by selective blockers of P2 purine receptors suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), while P1 blocker DPCPX was not effective. We conclude that Ap(n)As may be considered as new class of endogenous cardioinhibitory compounds. P2 purine receptors play the central role in mediation of Ap4A and Ap5A inhibitory effects on electrical and contractile activity in different regions of the rat heart.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

Commonly consumed beverages in daily life: do they cause atrial fibrillation?

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in the United States and worldwide. Caffeine, alcohol, and, more recently, energy drinks are the most commonly consumed beverages in daily living, especially by young individuals. Several questions have been raised about the implications of caffeine, alcohol, and energy drinks in cardiovascular health, especially in triggering AF. This review focuses on the role of these commonly consumed beverages as a cause of AF, with special emphasis of potential mechanisms and studies addressing this issue.

The effects of caffeine on the inducibility of atrial fibrillation

INTRODUCTION

There is widespread belief that caffeine consumption is linked to atrial arrhythmias; however, there is a relative lack of systematic evidence to support the assertion. The purpose of this study was to investigate whether caffeine, in doses equivalent to daily use in the general population, alter the propensity for atrial fibrillation (AF) in an experimental model comparing normal and simulated predisposition to AF.

METHODS AND MATERIAL

Caffeine (caffeine Na benzoate, 50:50 mixture) was administered intravenously at 1, 3, and 5 mg/kg doses in dogs producing serum levels of 2 to 4, 5 to 7, and 8 to 10 microg/mL. To simulate focal AF, premature stimulation from the right superior pulmonary vein was delivered at 2x, 4x, and 10x threshold at a rate of 180/min (S(1)-S(2) = 330 milliseconds) without and then with low-level stimulation of ganglionated plexi (GP) at the entrance of the right superior pulmonary vein. The window of vulnerability (WOV), a measure of the propensity for AF inducibility, was determined by the longest coupling interval of the premature beat (S(1)-S(2)) minus the shortest S(1)-S(2), which induced AF. The cumulative WOV is the sum of the individually determined WOV.

RESULTS

At each serum level of caffeine, the cumulative WOV was lower without rather than with GP stimulation compared with control. The cumulative WOV for both the stimulated, that is, predisposed to AF, and nonstimulated, that is, normal groups, exhibited a significantly lower average as compared with that exhibited by the control group (P <or= .003-.02).

CONCLUSION

These findings suggest that the presence of caffeine may result in an unexpected reduction in the propensity for AF in healthy individuals and in those with a predisposition for AF (enhanced AF inducibility caused by the stimulation of the GP).

Interrelationships Between the Autonomic Nervous System and Atrial Fibrillation

Mechanisms responsible for atrial fibrillation are not completely understood but the autonomic nervous system is a potentially potent modulator of the initiation, maintenance, termination and ventricular rate determination of atrial fibrillation. Complex interactions exist between the parasympathetic and sympathetic nervous systems on the central, ganglionic, peripheral, tissue, cellular and subcellular levels that could be responsible for alterations in conduction and refractoriness properties of the heart as well as the presence and type of triggered activity, all of which could contribute to atrial fibrillation. These dynamic inter-relationships may also be altered dependent upon other neurohumoral modulators and cardiac mechanical effects from ventricular dysfunction and congestive heart failure. The clinical implications regarding the effects of the autonomic nervous system in atrial fibrillation are widespread. The effects of modulating ganglionic input into the atria may alter the presence or absence of atrial fibrillation as has been highlighted from ablation investigations. This article reviews what is known regarding the inter-relationships between the autonomic nervous system and atrial fibrillation and provides state of the art information at all levels of autonomic interactions.