1,721,203 research outputs found
Management of atrial fibrillation in bradyarrhythmias
No full textSinus node disease (SND), a common indication to implant a pacemaker, is frequently associated with atrial fibrillation (AF), either at implantation (paroxysmal AF) or during follow-up, which often evolves to persistent or permanent AF. Pacemakers with an atrial lead allow continuous monitoring of the atrial rhythm and enable detection of the burden of AF. Asymptomatic atrial tachyarrhythmias, being associated with increased risk of stroke, have important prognostic implications, and their detection could guide decision-making about antithrombotic prophylaxis. Pacing mode and pacing algorithms can influence the occurrence of AF and atrial tachyarrhythmias. In DDD/DDDR pacing mode, reduction of unnecessary right ventricular pacing positively affects the occurrence and evolution of AF, but patients with a history of atrial tachyarrhythmias maintain an increased risk of arrhythmic events. In the MINERVA study, the use of algorithms that act in the atrium for preventive pacing and atrial antitachycardia pacing while minimizing right ventricular pacing was beneficial in patients with SND and previous atrial tachyarrhythmias, and was associated with a significant reduction in evolution to permanent AF. New information available on therapies delivered at the atrial level by implanted devices suggests clinical advantages that could improve current guidelines for the management of AF and atrial tachyarrhythmias
Cardiac Resynchronization Therapy: An Overview on Guidelines
No full textCardiac resynchronization therapy (CRT) is included in international consensus guidelines as a treatment with proven efficacy in well-selected patients on top of optimal medical therapy. Although all the guidelines strongly recommend CRT for LBBB with QRS duration greater than 150 milliseconds, lower strength of recommendation is reported for QRS duration of 120 to 150 milliseconds, especially if not associated with LBBB. CRT is not recommended for a QRS of less than 120 milliseconds. No indication emerges for guiding the implant based on echocardiographic evaluation of dyssynchrony. Many data indicate that CRT is underused and there is heterogeneity in its implementation
Cardiac Resynchronization Therapy: An Overview on Guidelines
No full textCardiac resynchronization therapy (CRT) is included in international consensus guidelines as a treatment with proven efficacy in well-selected patients on top of optimal medical therapy. Although all the guidelines strongly recommend CRT for LBBB with QRS duration greater than 150 milliseconds, lower strength of recommendation is reported for QRS duration of 120 to 150 milliseconds, especially if not associated with LBBB. CRT is not recommended for a QRS of less than 120 milliseconds. No indication emerges for guiding the implant based on echocardiographic evaluation of dyssynchrony. Many data indicate that CRT is underused and there is heterogeneity in its implementation
Arrhythmias Originating in the Atria
No full textAtrial flutter, atrial tachycardias, and atrial fibrillation are the main sustained atrial tachycardias. Reentry, increased automaticity, and triggered activity are atrial arrhythmia's main mechanisms. Atrial flutter is the clinical and theoretical model of reentry. Its classification is based on the atrial chamber involved and the arrhythmia's anatomic path. Ablative procedures for atrial fibrillation have created several new reentrant tachycardias. Electrocardiography (ECG) identifies the site of origin of focal atrial tachycardias and the mechanism of these arrhythmias. ECG is fundamental in the diagnosis of atrial fibrillation and often allows understanding of its mechanism of origin and maintenance
The QRS Complex. Normal Activation of the Ventricles
No full textThe ventricular conduction system starts below the His bundle, where it bifurcates into the right and left bundle branches that taper out to the subendocardial Purkinje network, which activates the ventricular myocardium. This system is responsible for the synchronized and almost simultaneous activation of both ventricles. On the surface ECG, the ventricular conduction system lies in the terminal portion of the PR interval, whereas the QRS complex is comprised of the electrical currents originating from ventricular depolarization. This article reviews the main electroanatomical features of the ventricular conduction system and the effects of its delay on the QRS
Advanced Concepts of Atrioventricular Nodal Electrophysiology: Observations on the Mechanisms of Atrioventricular Nodal Reciprocating Tachycardias
No full textAtrioventricular node reentrant tachycardia (AVNRT) is a supraventricular arrhythmia easily diagnosed by 12-lead electrocardiogram. What is far more challenging, is the understanding of the reentrant circuit in its typical and atypical presentations. The function of the atrioventricular node is still incomplete and this knowledge gap is reflected in the reconstruction of the pathways used by AVNRT in its multiform presentations. This article illustrates the heterogeneous electrocardiographic manifestations of AVNRT. We reconstruct the reentrant circuits involved using more recent understanding of the anatomic and electrophysiologic characteristics of the atrioventricular node
Intraventricular Delay and Blocks
No full textFrom the atrioventricular node, electrical activation is propagated to both ventricles by a system of specialized conducting fibers, His Purkinje System (HPS), guaranteeing a fast, synchronous depolarization of both ventricles. From the predivisional common stem, a right and left branch separate, subdividing further in a fairly predictable fashion. Synchronous ventricular activation results in a QRS with specific characteristics and duration of less than 110 milliseconds. Block or delay in any part of the HPS changes the electrocardiographic (ECG) morphology. This article discusses the use and limitations of standard ECG in detecting abnormal ventricular propagation in specific areas of the HPS
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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