The Cardiac Pacemaker Current if

Pacemaker Current if. Since the hyperpolarization-activated current, if, was originally associated with the diastolic depolarization phase of action potential in the sinoatrial (SA) node in 1979, its central role in the generation and control of pacemaker activity has become increasingly clear through a series of experimental findings, some of which have substantially modified the pre-existing theories of cardiac pacemaking and its modulation by the autonomic transmitters. Thus, the pacemaker current of Purkinje fibers, formerly described as a deactivating pure potassium (K) current, was found to be in fact, like the nodal if, inward and activating on hyperpolarization. Furthermore, in SA node cells, as well as mediating rhythm acceleration induced by catecholamines, if was found to underlie the slowing effect of low acetylcholine (ACh) concentrations, in contrast with the generally accepted hypothesis that activation of a K conductance is the main process responsible for cardiac slowing. A final, atypical property of if recently demonstrated concerns the activating action exerted on if by intracellular cAMP. Unlike that on other voltage-gated, cAMP-modulated cardiac channels, this action is independent of phosphorylation and involves a direct binding of cAMP to if channels. (J Cardiovasc Electrophysiol, Vol. 3, pp. 334–344, August 1992)     

Long‐Term Results of Transcatheter Atrial Fibrillation Ablation in Patients with Impaired Left Ventricular Systolic Function

AF Ablation and Impaired Left Ventricular Function. Introduction: Long‐term outcome of AF ablation in patients with impaired LVEF is unknown. The aim of this study is to evaluate sinus rhythm (SR) maintenance, clinical status, and echocardiographic parameters over a long‐term period following atrial fibrillation (AF) transcatheter ablation in patients with left ventricular ejection fraction (LVEF) <50%. Methods and Results: A total of 196 patients (87.2% males, age 60.5 ± 10.2 years) with LVEF <50% underwent radiofrequency transcatheter ablation for paroxysmal (22.4%) or persistent (77.6%) AF. Patients were followed up for 46.2 (16.4–63.5) months regarding AF recurrences, functional class, and echocardiographic parameters. All patients underwent pulmonary vein isolation, while 167 (85.2%) required additional atrial lesions. Eleven (5.6%) patients suffered procedural complications. During follow‐up, 58 (29.6%) patients required repeated ablations. At the follow‐up end, 15 (7.7%) patients died, while 74 (37.8%) documented at least one episode of AF, atrial flutter, or atrial ectopic tachycardia. Eighty‐three (47.2%) patients maintained antiarrhythmic drugs. During follow‐up, NYHA class improved by at least one class more frequently among patients maintaining SR compared to those experiencing relapses (70.6% vs 47.9%, P = 0.003). LVEF showed a broader relative increase in patients maintaining SR (32.7% vs 21.4%; P = 0.047) and mitral regurgitation grading significantly decreased (P <0.001) only within these patients. At multivariable analysis SR maintenance emerged as an independent predictor (odds ratio 4.26, 95% CI 1.69–10.74, P = 0.002) of long‐term clinical improvement (reduction in NYHA class ≥1 and relative increase in LVEF ≥10%). Conclusions: Although not substantially worse than in patients with preserved LVEF, AF ablation in patients with impaired LVEF is affected by high long‐term recurrence rate. Among these patients SR maintenance is associated with greater clinical improvement. (J Cardiovasc Electrophysiol, Vol. 24, pp. 24‐32, January 2013)     

Use of Implantable Cardioverter-Defibrillator in Inherited Arrhythmogenic Diseases: Data from Italian ICD Registry for the Years 2001–6

Background: Previous studies have demonstrated the lifesaving role of an implantable cardioverter-defibrillator (ICD) in high-risk patients with genetic arrhythmogenic diseases.
Aim: To evaluate the clinical data of patients with hypertrophic cardiomyopathy (HCM), arrhythmogenic right ventricular cardiomyopathy (ARVD/C), idiopathic ventricular arrhythmia (IDIO-VA) including Brugada syndrome, short QT syndrome, and long QT syndrome (LQT) enrolled in the Italian ICD Registry in the years 2001–6.
Methods: The survey collected prospectively clinical data and technical characteristics of ICD implants on the basis of EURID form.
Results: The number of patients was 1,274 in the HCM group, 520 in the ARVD/C group, 460 in the IDIO-VA group, and 245 in the LQT group. Primary prevention involved 29.5% of patients in the HCM group, 15.9% in the ARVD/C group, 16.9% in the IDIO-VA group, and 16.6% in the LQT group, respectively. Ventricular tachycardia and ventricular fibrillation were reported in 49.0% and 24.8% in the HCM group, 72.9% and 20.0% in the ARVD/C group, 48.2% and 42.9% in the IDIO-VA group, and 21.2% and 61.6% in the LQT group, respectively. Single-, dual-, and triple-chamber ICDs were implanted in 41.5%, 47.6%, and 10.9% in the HCM group; 57.9%, 36.7%, and 5.4% in the ARVD/C group; 55.0%, 45.0%, and 0% in the IDIO-VA group; and 57.4%, 42.6%, and 0% in LQT group, respectively.
Conclusion: ICD therapies in the years 2001–6 for patients with inherited arrhythmia syndromes were utilized in Italy in a still-limited number of patients. Secondary prevention represented the major indication for ICD implant and the majority of patients were treated by single-chamber ICDs.