Atrial fibrillation-the final frontier

Timing mechanisms to control heart rhythm and initiate arrhythmias: roles for intracellular organelles, signalling pathways and subsarcolemmal Ca2

Rhythms of electrical activity in all regions of the heart can be influenced by a variety of intracellular membrane bound organelles. This is true both for normal pacemaker activity and for abnormal rhythms including those caused by early and delayed afterdepolarizations under pathological conditions. The influence of the sarcoplasmic reticulum (SR) on cardiac electrical activity is widely recognized, but other intracellular organelles including lysosomes and mitochondria also contribute. Intracellular organelles can provide a timing mechanism (such as an SR clock driven by cyclic uptake and release of Ca²⁺, with an important influence of intraluminal Ca²⁺), and/or can act as a Ca²⁺ store involved in signalling mechanisms. Ca²⁺ plays many diverse roles including carrying electric current, driving electrogenic sodium-calcium exchange (NCX) particularly when Ca²⁺ is extruded across the surface membrane causing depolarization, and activation of enzymes which target organelles and surface membrane proteins. Heart function is also influenced by Ca²⁺ mobilizing agents (cADP-ribose, nicotinic acid adenine dinucleotide phosphate and inositol trisphosphate) acting on intracellular organelles. Lysosomal Ca²⁺ release exerts its effects via calcium/calmodulin-dependent protein kinase II to promote SR Ca²⁺ uptake, and contributes to arrhythmias resulting from excessive beta-adrenoceptor stimulation. A separate arrhythmogenic mechanism involves lysosomes, mitochondria and SR. Interacting intracellular organelles, therefore, have profound effects on heart rhythms and NCX plays a central role. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Perspective on Antiarrhythmic Drug Combinations

Physicians use multiple drugs in combination to treat hypertension, heart failure, diabetes mellitus, angina, hyperlipidemia, and many other cardiovascular conditions and risk factors. However, administering antiarrhythmic drugs (AAD) in combination is rarely discussed. Yet, the possibility of increasing efficacy and/or tolerance and/or safety of AADs (by adding mechanisms, offsetting adverse mechanisms, and/or using lower doses) exists. Unfortunately, this topic has not been reviewed in any contemporary cardiac literature of which we are aware, although information regarding AAD combinations has been published. In conclusion, and accordingly, this review discusses the possibility of using AAD combinations for both ventricular arrhythmias and atrial fibrillation, in which the rationale for such combinations, considerations for such combinations, and supporting literature are covered.

Association between outpatient visits following hospital discharge and readmissions among Medicare beneficiaries with atrial fibrillation and other chronic conditions

Atrial fibrillation (AF) afflicts nearly 3 million people in the United States annually, the large majority of whom are Medicare beneficiaries with other chronic illnesses. Beneficiaries with multiple chronic conditions have high hospitalization and readmission rates but evidence on factors associated with readmissions is limited, and little is known about differences in rates between beneficiaries with and without AF. In a retrospective analysis of Medicare claims data, the relationship between outpatient visits within 14 days after hospital discharge and readmission was examined for beneficiaries with AF or other chronic conditions. About half of those beneficiaries with a hospitalization had an outpatient visit within 14 days of discharge. Readmission rates were 11% to 24% lower for beneficiaries with an outpatient visit than for those without one (P < .01). These findings suggest that follow-up care shortly after discharge may lower readmissions for patients with AF or other chronic conditions.

Advances in the management of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia worldwide, increasing in incidence with the aging population. Substantial morbidity and mortality accompany its diagnosis. Management should focus on rate and rhythm management, on reducing thromboembolic risk, and also potentially on targeting the mechanisms responsible for its perpetuation. Current antiarrhythmic therapy has only modest efficacy and substantial side effects, and anticoagulation regimes are cumbersome and require regular monitoring. Novel anticoagulants and antiarrhythmics hold the promise of improved efficacy and safety. This review covers current therapy for AF, major advances in pharmacological management and future directions for therapy.