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Pathophysiology Bundle branch reentrant (BBR) ventricular tachycardia (VT) is a reentrant VT with a well-defined macroreentry circuit, incorporating the right bundle branch (RB) and left bundle branch (LB) as obligatory limbs of the circuit, connected proximally by the His bundle (HB) and distally by the ventricular septal myocardium ( Fig. 30.1 ). The QRS during BBR VT can display either left bundle branch block (LBBB) or…

Pathophysiology Cardiomyopathies are traditionally defined on the basis of structural and functional phenotypes, notably dilated, hypertrophic, restrictive, and arrhythmogenic. Dilated cardiomyopathy (DCM) is characterized by ventricular dilatation and systolic dysfunction in the absence of known abnormal loading conditions or significant coronary artery disease. DCM is not a single disease entity and can be related to a variety of causes, including genetic, infectious, toxic, metabolic, and endocrine,…

Pathophysiology The His-Purkinje system plays an important role in the genesis of cardiac arrhythmias. The mechanism of several types of monomorphic ventricular tachycardias (VTs) has been directly linked to the Purkinje system, including bundle branch reentrant VT, interfascicular reentrant VT, fascicular reentrant VT, and focal nonreentrant fascicular VT. A subset of polymorphic VTs and ventricular fibrillation have also been linked to triggers originating from the Purkinje…

Pathophysiology Ventricular tachycardia (VT) is usually associated with structural heart disease, most commonly coronary artery disease and cardiomyopathy. However, about 10% of patients who present with VT have no obvious structural heart disease (idiopathic VT). Absence of structural heart disease is usually suggested if the ECG (except in Brugada syndrome and long QT syndrome), echocardiogram, and coronary arteriogram collectively are normal. Nevertheless, cardiac magnetic resonance (CMR)…

Classification of ventricular tachyarrhythmias Ventricular tachycardia (VT) is defined as a tachycardia (rate >100 beats/min) with three or more consecutive beats that originates below the bifurcation of the His bundle (HB), in the specialized conduction system, the ventricular muscle, or in a combination of both tissues, independent of atrial and atrioventricular nodal (AVN) conduction. Classification according to tachycardia morphology Monomorphic VT has a single stable QRS…

Clinical considerations Causes of wide complex tachycardias A narrow QRS complex (120 milliseconds or less) requires rapid, highly synchronous electrical activation of the right and left ventricles, which can only be achieved through the specialized, rapidly conducting His-Purkinje system (HPS). A wide QRS complex implies less synchronous ventricular activation of longer duration, which can be due to intraventricular conduction disturbances (IVCDs), or ventricular activation not mediated…

A “supraventricular” origin of a tachycardia implies the obligatory involvement of one or more cardiac structures above the bifurcation of the His bundle (HB), including atrial myocardium, atrioventricular node (AVN), proximal HB, coronary sinus (CS), pulmonary veins, venae cavae, or abnormal atrioventricular (AV) connections other than the HB (i.e., bypass tracts [BTs]). Narrow QRS complex supraventricular tachycardia (SVT) is a tachyarrhythmia with a rate greater than…

A working definition of an atypical bypass tract (BT) is a conduction pathway that bypasses all or part of the normal conduction system but is not a rapidly conducting pathway connecting atrium and ventricle near the mitral or tricuspid annulus. Thus, pathways that connect the atrium to the His bundle (HB, atrio-Hisian BT), the atrioventricular node (AVN) to the His-Purkinje system (HPS; nodofascicular BT) or the…

Types of bypass tracts Bypass tracts (BTs) are remnants of the atrioventricular (AV) connections caused by incomplete embryological development of the AV annuli and failure of the fibrous separation between the atria and ventricles. There are several types of BTs, according to the structures they connect, including atrioventricular, atrionodal, atrio-Hisian, atriofascicular, fasciculoventricular, and nodofascicular BTs. Atrioventricular bypass tracts Atrioventricular BTs are strands of working myocardial cells…

Anatomy and physiology of the atrioventricular node The atrioventricular node (AVN) is the only normal electrical connection between the atria and the ventricles; the fibrous skeleton acts as an insulator to prevent electrical impulses from entering the ventricles by any other route. The main function of the AVN is modulation of atrial impulse transmission to the ventricles; it introduces a delay between atrial and ventricular systole,…

Anatomy and physiology of the sinus node The sinus node is a crescent-shaped, subepicardial specialized muscular structure located posterolaterally in the right atrial (RA) free wall. The sinus node lies within the epicardial groove of the sulcus terminalis, at the junction of the anterior trabeculated RA appendage with the posterior smooth-walled venous component. The endocardial aspect of the sulcus terminalis is marked by the crista terminalis.…

Risk of thromboembolism Atrial fibrillation (AF) is a major risk factor for thromboembolism, causing approximately 15% of the ischemic strokes in the United States, 36% of strokes in patients older than 80 years, and up to 20% of cryptogenic strokes. Moreover, cardioembolic strokes caused by AF are large and multiple, often involve bilateral infarcts, and are associated with the highest rates of mortality and permanent disability.…

Management of atrial fibrillation (AF) should be aimed at identifying and treating underlying causes and predisposing conditions of the arrhythmia, as well as reducing symptoms, improving quality of life, and preventing cardiovascular morbidity and mortality associated with AF. There are four main issues that must be addressed in the treatment of AF: (1) prevention of systemic thromboembolism; (2) ventricular rate control; (3) restoration and maintenance of…

Clinical presentation Symptomatic atrial fibrillation Atrial fibrillation (AF) can be symptomatic or asymptomatic, even in the same patient. Symptoms associated with AF vary, depending on the ventricular rate, the underlying functional status, the duration of AF, the presence and severity of structural heart disease, and the individual patient’s perception. Of note, women with AF are more likely to report more clinical symptoms and poorer quality of…

Classification of atrial fibrillation Atrial fibrillation (AF) has been described as lone, idiopathic, nonvalvular, valvular, paroxysmal, persistent, or permanent. Each of these classifications has implications regarding mechanisms as well as response to therapy. At the initial detection of AF, it is impossible to know the subsequent pattern of duration and frequency of recurrences. Thus, a designation of the first-detected episode of AF is made on the…

Pathophysiology Cardiac arrhythmias are a common problem in patients with congenital heart disease (CHD), particularly after they have undergone reparative or palliative surgical procedures. Atrial tachyarrhythmias are the most prevalent, with a lifetime risk of approximately 50%, regardless of the severity of the congenital defects. Macroreentry localized to the right atrium (RA) is the most common mechanism, followed by atrial fibrillation (AF). Focal atrial tachycardias (ATs)…

Pathophysiology Organized atrial tachycardias (ATs) are broadly categorized as either focal (centrifugal activation originating from a discrete site that incorporates automaticity, triggered activity, and microreentrant mechanisms) or macroreentrant (a relatively large reentrant circuit around a central obstacle). Depending on whether or not the cavotricuspid isthmus (CTI) is critical to the reentry circuit, macroreentrant ATs (MRATs) are divided into two groups: “CTI-dependent” MRAT or “non-CTI-dependent” MRAT (see…

Organized atrial tachycardias (ATs) are broadly categorized as either focal or macroreentrant (see Table 12.1 ). Focal ATs exhibit a centrifugal activation pattern originating from a discrete site and can have automaticity, triggered activity, and microreentrant mechanisms (see Video 12.1 ). A macroreentrant AT incorporates a relatively large reentrant circuit around a central obstacle (see Video 7.5 ). Depending on whether or not the cavotricuspid isthmus…

Classification of atrial tachycardias Organized atrial tachycardias (ATs) are broadly categorized as either focal (originating from a small circumscribed area from which it spreads out generally centrifugally; Video 12.1 ) or macroreentrant (continuous, uninterrupted activation wavefront rotating around a relatively large central obstacle; see Video 7.5 ). Focal ATs can be caused by automatic, triggered, or microreentrant mechanisms. The mechanism of macroreentrant AT is reentrant activation…