Definitions Ventricular tachycardia (VT) is defined as a tachycardia (rate > 100 beats per minute [bpm]) with three or more consecutive beats that originates in the ventricles. , Accelerated idioventricular rhythm denotes a ventricular rhythm less than 100 bpm. Sustained ventricular tachycardia lasts more than 30 seconds (unless requiring termination because of hemodynamic collapse), whereas nonsustained tachycardia terminates spontaneously within 30 seconds. Monomorphic ventricular tachycardia has…

Definitions The anatomic basis of atrioventricular reentrant tachycardia (AVRT) is an abnormal connection ( accessory pathway [AP] ) between the atrial and ventricular myocardium. One limb of the reentrant circuit is the atrioventricular (AV) node and the other is the AP. On rare occasions the circuit includes two or more APs. The term preexcitation refers to earlier activation of the ventricle by a wave front arising…

Atrioventricular nodal reentrant tachycardia Definition Atrioventricular nodal reentrant tachycardia (AVNRT) denotes reentry in the area of the atrioventricular (AV) node. Several models have been proposed to explain the mechanism of the arrhythmia in the context of the complex anatomy of the AV node and its atrial extension, but its exact circuit remains elusive. Pathophysiology The concept of dual AV nodal pathways as the substrate for AVNRT…

Definitions and classification Atrial fibrillation (AF) is characterized by uncoordinated atrial activation without effective atrial contraction. On the electrocardiogram (ECG), AF is characterized by rapid oscillations or fibrillatory waves that vary in amplitude, shape, and timing; that usually have a cycle length less than 200 ms; and that are associated with an irregular ventricular response. QRS complexes may also be of variable amplitude. Regular R-R intervals…

Atrial premature beats An atrial premature beat (APB) is characterized by a nonsinus P wave that occurs before the next anticipated sinus beat. Several electrocardiographic leads may be needed to distinguish P waves originating in the sinus node versus an ectopic focus. In the rare case of sinus nodal premature beats, the P wave will be identical. The post-extrasystolic cycle length is typically less than compensatory…

Wide-QRS tachycardias can be ventricular tachycardia (VT), supraventricular tachycardia (SVT) conducting with bundle branch block (BBB) aberration or through a bystander accessory pathway (AP), or an AP-mediated tachycardia, with reported proportions of 80%, 15%, and 5%, respectively. , The correct diagnosis of VT is critical to management because misdiagnosis and administration of drugs usually used for SVT can be harmful for patients in VT. Therefore the…

Narrow-QRS complexes (≤120 ms) are due to activation of the ventricles via the His-Purkinje system, consistent with origin of the arrhythmia above or within the His bundle. However, early activation of the His bundle can also occur in high septal ventricular tachycardias (VTs), thus resulting in relatively narrow-QRS complexes (110–140 ms). In these cases the HV interval is less than 35 ms. Atrial fibrillation (AF) with…

Sinus bradycardia Sinus rates less than 60 beats per minute (bpm) are defined as bradycardia in adults. , Lower rates are common in well-trained athletes and occasionally in the young. During sleep the sinus rate may fall to 35 bpm with pauses up to 3 seconds and this is not considered abnormal. Sinus arrhythmia usually refers to sinus cycle phasic variation that is related to the…

Radiofrequency ablation Radiofrequency (RF) ablation induces tissue necrosis by heating the targeted tissue. Most cardiac ablation systems deliver RF energy between a unipolar platinum-iridium electrode at the tip of the ablation catheter and a large dispersive grounding patch on the patient’s skin, typically on the abdomen or thigh ( Fig. 8.1 ). Ablation catheters also have electrodes to record electrical activity from within the heart (…

Electroanatomic mapping Theoretical considerations During conventional electrophysiology (EP) procedures, catheters are manually navigated with the use of single or bi-plane fluoroscopy. An inherent limitation of fluoroscopic navigation is that orientation of the catheter relative to the cardiac anatomy can only be appreciated in two dimensions. Thus it may make complex procedures challenging and is associated with radiation exposure for both patient and physician. In 1996 Ben-Haim…

Basic intervals Basic intervals during sinus rhythm represent a quantitative assessment of the electrical activation of the heart. Normal atrial activation begins at the sinus node, spreads to the low atrium and atrioventricular (AV) junction, and then to the left atrium ( Fig. 6.1 ). Occasionally, the low-right atrium is activated slightly later than the atrium recorded at the AV junction. Activation of the left atrium…

Electrode catheters Basic mapping catheters Catheters used for electrophysiology studies (EPSs) and ablation are composed of multiple insulated wires encased in woven Dacron or polyurethane. Electrodes used in electrophysiology (EP) catheters are usually made of polished platinum-iridium alloy. Platinum is an inert and biologically safe metal with excellent electrical properties but is mechanically soft. The addition of iridium improves mechanical strength without affecting electrical performance. Electrode…

Patient preparation Patients should be studied in the postabsorptive state and after beta blockers or other antiarrhythmic agents have been discontinued for at least 5 days. Amiodarone should be withdrawn at least 2 months before the procedure if feasible. A transesophageal echocardiogram is recommended to exclude intracardiac thrombi in patients with atrial fibrillation (AF) or atrial flutter and is particularly important in such patients who have…

Some of the descriptive terms conventionally used for cardiac structures are inaccurate. Conventionally the heart and its associated structures have been described in accordance with their position when the heart has been removed from the body and positioned with the apex down, rather than according to their in vivo positions. , For example, when defining positions along the mitral and tricuspid valve annuli and the triangle…

Normal excitation of the heart Cardiac electrical activity starts by the spontaneous excitation of “pacemaker” cells in the sinoatrial node in the right atrium. Pacemaker automaticity is due to spontaneous diastolic repolarization of phase 4 that generates rhythmic action potentials and determines the heart rate through various currents, including the If current. There are no histologically specialized conduction tissues between the sinus and AV node, and…

Bradyarrhythmias are due to sinus nodal disease ( Box 1.1 ) or atrioventricular conduction block ( Box 1.2 ). Box 1.1 Sinus Node Dysfunction (with accompanying symptoms) Sinus bradycardia Sinoatrial exit block Sinus pauses (>3 s) Sinus node arrest Tachycardia-bradycardia syndrome Chronotropic incompetence * * Maximum predicted heart rate is calculated as 220 – age (y). Box 1.2 AV. Atrioventricular. Atrioventricular Block First-degree AV block Second-degree…