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Recognition of common arrhythmias
Published in John Edward Boland, David W. M. Muller, Interventional Cardiology and Cardiac Catheterisation, 2019
Nicholas P. Kerr, Rajesh N. Subbiah
Atrioventricular re-entrant tachycardia (AVRT) is the second commonest cause of paroxysmal SVT. AVRT is more common in males than females and generally presents at a younger age than AVNRT. It occurs in patients with an accessory AV pathway (also called bypass tract) that allows AV (and/or VA) conduction via another route than the normal AV node-His Purkinje system. Accessory pathways may conduct in both antegrade and retrograde directions, retrograde only, or uncommonly, antegrade direction only. When capable of conducting antegrade, accessory pathways cause pre-excitation pattern on the ECG. This occurs as conduction proceeds over the accessory pathway to activate the ventricles at another site earlier than conduction over the AV node. Pre-excitation on the ECG is manifest as a short PR interval, a wide QRS complex and a slurred onset to QRS called a ‘delta wave’. When the ECG shows pre-excitation, the accessory pathway is said to be a manifest bypass tract. If the accessory pathway can only conduct in the retrograde direction, it is called a concealed bypass tract. Occasionally, there is no evidence of pre-excitation at rest but at increased sinus rates, more activation occurs over the accessory pathway so that pre-excitation becomes apparent. This is called a latent pathway. Patients with manifest pre-excitation and paroxysmal SVT have Wolff–Parkinson–White (WPW) syndrome. In the absence of symptoms, a patient with an ECG appearance of pre-excitation is said to have WPW pattern.
Catheter ablation of supraventricular tachycardia
Published in Ever D. Grech, Practical Interventional Cardiology, 2017
Christopher Madias, Mark S Link
After catheters are placed, an evaluation of the underlying electrical substrate is undertaken. AVNRT requires dual AV nodal physiology with the presence of a slow pathway revealed with pacing manoeuvres. AVRT requires the presence of a bypass tract that is often observed early in the EP study. Bypass tracts might be concealed on a surface ECG (lack of a delta wave) because they only conduct in a retrograde fashion or because of rapid AV nodal conduction – in which case AV nodal conduction precedes conduction via the bypass tract.7 The pattern of retrograde conduction and pacing to AV and ventriculoatrial (VA) Wenckebach and 2-1 heart block will generally rapidly uncover bypass tracts. By pacing in the ventricle, retrograde conduction and activation of the atrial tissue as observed on the CS, His bundle and right atrial catheters can be concentric or eccentric. A concentric pattern refers to midline VA conduction through or near the AV node. Eccentric conduction suggests initial activation of the atria is via a discrete bypass tract apart from the AV node (Figure 39.3). Concentric VA conduction can also be present with septal bypass tracts, but these can be differentiated from AV nodal conduction, as they usually do not show decremental properties. Para-Hisian pacing is another helpful manoeuvre to uncover septal bypass tracts (Figure 39.4).8 Para-Hisian pacing is performed by pacing from the distal pole of the His catheter and measuring VA conduction times. In addition to capturing local ventricular myocardium, by pacing at maximal energy outputs, the insulation surrounding the His–Purkinje fibres can be penetrated and ventricular activation proceeds via the specialised conduction system, resulting in a narrow QRS. With decreased pacing outputs, the His–Purkinje system will no longer be captured and the QRS will widen. In the absence of a septal bypass tract, retrograde activation of the atrium travels through the His–Purkinje system and the AV node. If there is capture of the His then retrograde conduction occurs rapidly and the VA time is short; however, when the His is no longer captured, the impulse must travel down to the apex of the RV and then retrogradely through the His–Purkinje system, thereby lengthening the VA time. In the presence of a septal bypass tract, VA conduction time and activation sequence will be similar whether or not the His–Purkinje network is captured.
Cardiac arrhythmias in pregnant women: need for mother and offspring protection
Published in Current Medical Research and Opinion, 2020
Theodora A. Manolis, Antonis A. Manolis, Evdoxia J. Apostolopoulos, Despoina Papatheou, Helen Melita, Antonis S. Manolis
Fetal VT with rates >200 bpm has been noted in fetuses with AV block, cardiac tumors, acute myocarditis, channelopathies (e.g. LQTS), and CHD146. Prenatal diagnosis and treatment of VT remains a difficult task152. Fetal M-mode can help diagnose VT by showing ventricular rate higher than atrial rate with AV dissociation153. In cases of VT where there is a retrograde 1:1 VA conduction, it is not possible to differentiate VT from SVT by fetal cardiac ultrasound. LQTS may be suspected when tachyarrhythmias and bradyarrhythmias coexist; fetal magnetocardiography (fMCG) may aid in rendering a specific diagnosis by revealing QT prolongation and TdP154,155. Fetal LQTS may be diagnosed by an fMCG-recorded QTc >490 ms with a reported 89% sensitivity and specificity; fetal TdP has been noted when QTc is ≥620 ms156. In a series of 173 pediatric cases with cardiac tumors, with rhabdomyoma being the most common (∼60%) and fibromas the second most common type (∼15%), arrhythmias occurred in 24%, with VT being the most common arrhythmia, more frequently (64%) associated with fibromas; a significant percentage of patients (42%) with rhabdomyomas was diagnosed during a prenatal ultrasound157.
Ventriculoatrial synchrony induced heart failure
Published in Acta Clinica Belgica, 2018
Stefan Andric, Dragica Tesic, Dalibor Somer, Ilija Srdanovic, Tatjana Miljkovic, Djordje G. Jakovljevic, Lazar Velicki
VA conduction can be present even when the patient has complete AV block. Atrial lead displacement and consequently loss of atrial capture with preserved sensing can be a predisposing factor for initiation of VA synchrony. Permanent VA synchrony may provoke aggravation of HF with mid-range EF in two different ways. Sustained pacemaker-mediated tachycardia, as a type of rapid ventricular pacing, may lead to a reduction in left ventricle EF. Constant retrograde propulsion of blood to pulmonary veins, coupled with the loss of atrial kick during RNRVAS-like condition, leads to impaired hemodynamics and severe lung congestion.