Select Articles Published on the Topic of Arrhythmia and Electrophysiogy in 2013
Journal: Circulation (2014)

Noninvasive atrial fibrillation (AF) therapies are based on 2 separate strategies: rate or rhythm control aiming to slow ventricular rate to normal or to restore sinus rhythm, respectively.Hence, in rate control, AF itself is not resolved, whereas the curtailment of ventricular frequency reduces exercise tolerance.Rhythm control, on the other hand, is hampered by adverse effects such as ventricular proarrhythmia.Therefore, better insight into the contribution of ion channels, present in the atria but not the ventricles, to AF and the concordant exploration of possible atrium-specific therapies are essential if we are to diminish the burden of adverse effects in AF treatment.Previous studies showed that the acetylcholine-dependent potassium current (I K,ACh ), governed by the atrium-specific Kir3.x channels, can become constitutively active (I K,ACh-C ) in patients with AF.In the present study, we demonstrate the contribution of I K,ACh-C and Kir3.x to the initiation, maintenance, and termination of AF.We show for the first time that I K,ACh-C increases the chance of AF initiation through its steepening effects on the action potential duration and conduction velocity restitution curves, causing action potential duration and amplitude alternans.In addition, I K,ACh-C is shown to facilitate AF maintenance by stabilizing rotor dynamics, whereas AF termination can be elicited by blockade of I K,ACh-C , causing alternans-mediated rotor destabilization.Our findings provide evidence for a causal relationship between I K,ACh-C , alternans, and the initiation, maintenance, and termination of AF.Thus, not only I K,ACh-C or Kir3.x but also its consequent alternans might be an interesting atrium-specific target for future AF rhythm control or pharmacological cardioversion.Conclusions-Atrium-specific Kir3.x controls the induction, dynamics, and termination of fibrillation by modulating APD and APD/conduction velocity restitution slopes in atrial tissue with I K,ACh-c .This study provides new molecular and mechanistic insights into atrial tachyarrhythmias and identifies Kir3.x as a promising atrium-specific target for antiarrhythmic strategies. 1 Incident Atrial Fibrillation Among Asians, Hispanics, Blacks, and WhitesSummary-Although atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice, the underlying mechanisms responsible for its induction and perpetuation remain incompletely understood.Blacks experience a substantially lower rate of AF compared with whites, and the relative strength of this association suggests the mechanism responsible for the race-AF association plays an important role in disease pathogenesis.Because AF rates have only been rigorously compared between black and white patients, it is unclear whether white race confers elevated AF risk or black race affords arrhythmia protection.The present investigation compared incident AF between whites, blacks, Hispanics, and Asians receiving hospital-based medical care in California.A significantly lower hazard of AF was observed among blacks, Hispanics, and Asians compared with whites both before and after controlling for established risk factors.These findings argue against a protective effect unique to black race and instead suggest an unidentified characteristic inherent to white race increases AF risk.In addition, the difference in AF risk between whites and nonwhites was most pronounced in the absence of established AF risk factors.This further suggests that an unknown, alternative disease mechanism is driving these racial differences.As nonwhite racial and ethnic populations within the United States continue to grow, clinicians should be aware of the importance of race in AF prediction and incorporate this knowledge into their care of patients at risk for this frequently encountered disease.Conclusions-In a large hospital-based cohort, whites have an increased risk of AF whether compared with blacks, Asians, or Hispanics.The heightened AF risk among whites is most pronounced in the absence of cardiovascular comorbidities. 2 Intramyocardial Adiposity After Myocardial Infarction: New Implications of a Substrate for Ventricular TachycardiaSummary-The prevalence of intramyocardial adipose tissue (IMAT) in patients after myocardial infarction is ≈15% to 89%, depending on disease progression and assessment modality.To date, the electrophysiological influence of IMAT in this setting has been undefined.In this large-animal study, we have provided histological and electrophysiological evidence that IMAT is associated with ventricular tachycardia in the chronic phase of myocardial infarction.If these findings are confirmed clinically, noninvasive identification of IMAT within infarct borders may be applied to predict the propensity for ventricular tachycardia and mortality.The "gray zone"