Giuseppe Bagliani

P Wave Assessment: State of the Art Update

Diagnostic (mapping) and therapeutic (ablation, pacing) advances have provided insight into atrial depolarization processes and new developments in P wave analysis. Information about interatrial pathways is important to the understanding of interatrial conduction delay. A standardized method for P wave analysis is necessary for the development of a clinical role for management of patients with paroxysmal atrial fibrillation using signal-averaged P wave analysis and P wave dispersion. Algorithms for predicting localization of ectopic P waves may facilitate catheter ablation. P wave changes due to pacing at different atrial sites may be useful for permanent pacing for prevention of atrial fibrillation. Introduction of these developments into clinical practice should allow better prevention and treatment of atrial arrhythmias and could have considerable impact in view of their high frequency especially in the older population.

Atrial Activation Analysis by Surface P Wave and Multipolar Esophageal Recording After Cardioversion of Persistent Atrial Fibrillation

We studied atrial activation during sinus rhythm by combining 12‐lead ECG and multipolar esophageal recordings in 30 patients after electrical cardioversion of persistent atrial fibrillation. The primary endpoint was to establish a correlation between atrial activation evaluated by the two methods. Total P wave duration and morphology in inferior leads identified three patterns: normal P wave, late‐positive P wave, and late‐negative P wave. Proximal and distal esophageal recording characterized the longitudinal direction of activation of the posterior left atrium. We distinguished three activation patterns: normal activation when the interatrial conduction time is normal and depolarizes in craniocaudal direction, delayed activation when the interatrial conduction time is prolonged and the craniocaudal activation is maintained, and finally reversed activation when the posterior left atrium depolarizes in a reversed caudocranial direction. Four patients showed a normal P wave and also had a normal esophageal activation. Twelve patients showed a prolonged P wave (associated with delayed esophageal activation in 10 patients and reversed activation in 2 patients); 14 patients had a late‐negative P wave (all associated with a reversed esophageal activation). A high correlation existed between each pattern obtained by surface ECG and esophageal recording (P < 0.001) and between surface P wave duration and interatrial conduction time (R2= 0.64, P < 0.001). Much information concerning atrial activation can be obtained by meticulous analysis of the P wave, particularly its terminal part. Multipolar esophageal recording can be used when surface ECG appears unclear. (PACE 2003; 26:1178–1188)

PR Interval and Junctional Zone

The atrioventricular junction is a pivotal component of the cardiac conduction system, a key electrical relay site between the atria and the ventricles. The sophisticated functions carried out by the atrioventricular junction are possible for the presence of a complex apparatus made of specialized anatomic structures, cells with specific ion-channel expression, a well-organized spatial distribution of intercellular junctions (connexins), cells with intrinsic automatism, and a rich autonomic innervation. This article reviews the main anatomic and electrophysiologic features of the atrioventricular junction, with a focus on cardiac preexcitation.

General Approach to a Wide QRS Complex

Wide QRS complex is present when the normal activation pattern is modified by various mechanisms and clinical conditions. Correct interpretation is crucial for appropriate decision making. When approaching an electrocardiogram (ECG) with wide complex tachycardia, one must differentiate between ventricular tachycardia and supraventricular tachycardia conducted with aberrancy. ECG criteria are used and algorithms developed to aid in differential diagnosis. They are based on finding ECG signs of ventriculoatrial dissociation and QRS morphologies inconsistent with classic bundle branch block. The conditions able to modify structurally the normal activation of the heart may alter spontaneous ventricular activation during supraventricular tachycardia, creating differential diagnosis problems.

P Wave and the Substrates of Arrhythmias Originating in the Atria

The sinus node is the primary cardiac pacemaker from which the wavefront of activation proceeds through bundles of atrial fibers to the atrioventricular node. Left atrial activation proceeds along the Bachmann bundle and lower right atrium, determining P-wave morphology. Electrocardiogram reveals ectopic or retrograde atrial activation, wandering pacemaker activity, or artificial pacemaker-mediated atrial depolarization. Vectorcardiography and transesophageal recording are complementary methods. Atrial anatomic structure and automatic cells outside the sinus node constitute the mechanisms of focal and reentrant atrial arrhythmias. Arrhythmias with specific arrhythmogenic mechanisms correspond to precise electrocardiographic morphology for accurate diagnosis.

Arrhythmias Involving the Atrioventricular Junction

The atrioventricular junction has a central role in electrophysiology, responsible for reentrant and automatic forms of supraventricular tachycardia. During atrioventricular nodal reentry tachycardia, the circuit involves 2 electrophysiologically separate pathways located in the vicinity of the atrioventricular node. Atrioventricular reentry tachycardia is caused by the presence of an accessory pathway located almost anywhere along the atrioventricular groove; the macroreentrant circuit involves the atrioventricular node, the accessory pathway and necessarily portions of atria and ventricles. Junctional tachycardia is a rare form of nonparoxysmal supraventricular tachycardia, secondary to enhanced automaticity or triggered activity. By analyzing a 12-lead electrocardiogram during sinus rhythm and tachycardia, it is possible to accurately diagnose the specific type of supraventricular tachycardia.

Normal Ventricular Repolarization and QT Interval: Ionic Background, Modifiers, and Measurements

The QT interval on surface electrocardiogram represents the sum of depolarization and repolarization process of the ventricles. The ventricular recovery process, reflected by ST segment and T wave, mainly depends on the transmembrane outward transport of potassium ions to reestablish the endocellular electronegativity. Outward potassium channels represent a heterogeneous family of ionic carriers, whose global kinetics is modulated by heart rate and autonomic nervous activity. Several cardiac and noncardiac drugs and disease conditions, and several mutations of genes encoding ionic channels, generating distinct genetic channellopathies, may affect the ventricular repolarization, provoke QT interval prolongation and shortening, and increase the susceptibility to ventricular arrhythmias.

Arrhythmias Originating in the Atria

Atrial flutter, atrial tachycardias, and atrial fibrillation are the main sustained atrial tachycardias. Reentry, increased automaticity, and triggered activity are atrial arrhythmias main mechanisms. Atrial flutter is the clinical and theoretical model of reentry. Its classification is based on the atrial chamber involved and the arrhythmias 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.

Peculiar Electrocardiographic Aspects of Wide QRS Complex Tachycardia: When Differential Diagnosis Is Difficult

Wide complex tachycardia may represent a challenge for correct interpretation of standard electrocardiogram, which is crucial for proper patient management. For this reason, algorithms based on electrocardiographic criteria have been developed to guide interpretation in a step-by-step approach. Despite their greater accuracy, some cases of wide QRS complex tachycardia are a challenge. Some peculiar forms of ventricular tachycardia, and complex supraventricular substrate or particular clinical condition, may originate a challenging electrocardiographic pattern. In this article, a series of peculiar cases of wide QRS complex tachycardia is presented as paradigm of how important a comprehensive clinical approach is in these patients.

Atrioventricular Nodal Conduction Disease

This article describes the different anatomic structures involved in normal atrioventricular conduction and their pathologic states. It defines their effects on the electrocardiogram, and describes how to localize the level and evaluate the severity of conduction disease by electrocardiographic analysis. It illustrates the relevance of intracavitary recordings in the diagnosis of level of block.