W hen confronted with a tachycardia having a broad QRS complex, it is important to be able to diVerentiate between a supraventricular and a ventricular tachycardia. Medication given for the treatment of a supraventricular tachycardia (SVT) may be harmful to a patient with a ventricular tachycardia (VT).1 2 A reasonable haemodynamic condition during a tachycardia may erroneously lead to the wrong diagnosis of SVT.3 Familiarity with the ECG signs allowing the diagnosis of a VT is therefore essential. But as will be discussed here, the ECG should not only tell you how to distinguish VT from other tachycardias with a broad QRS complex, but also to suspect its aetiology and its site of origin in the ventricle. Both aspects are important in decision making about the prognostic significance of VT and correct treatment.
Classification of tachycardias with a broad QRS complexAs shown in fig 1, broad QRS tachycardia can be divided in three groups. x SVT with bundle branch block-Bundle branch block (BBB) may be pre-existing or can occur when the refractory period of one of the bundle branches is reached because of the heart rate of the SVT (so called tachycardia related or phase 3 block). BBB can also occur because of retrograde invasion in one of the bundle branches. 4 These causes of BBB can be found in patients with atrial tachycardia, atrial flutter, atrial fibrillation, atrioventricular (AV) nodal tachycardia, and also during orthodromic circus movement tachycardia (with AV conduction over the AV node and ventriculo-atrial (VA) conduction over an accessory AV pathway).x SVT with AV conduction over an accessory AV pathway-This may occur during atrial tachycardia, atrial flutter, atrial fibrillation, AV nodal tachycardia, and during antidromic circus movement tachycardia (with AV conduction over an accessory AV pathway and VA conduction over the AV node or a second accessory AV pathway). It is also the case in the so called Mahaim tachycardia where AV conduction goes by way of a slowly conducting right sided accessory AV pathway or a nodo-ventricular fibre inserting into the right ventricle.
During the last 40 years, much progress has been made in our understanding and management of cardiac arrhythmias. A major step in the late 1960s was to combine programmed electrical stimulation of the heart with intracardiac activation recording. This allowed: 1) localization of the site of the block in the atrioventricular conduction system in patients with bradycardia; and 2) identification of the site of origin and the mechanism of supraventricular and ventricular tachycardia. Combining information from intracardiac studies with findings on the 12-lead electrocardiogram (ECG) resulted in much better localization of conduction abnormalities and arrhythmias using the ECG. This new knowledge led to the development of new therapies, such as bradycardia and antitachycardia pacing, and surgery for supraventricular and ventricular tachycardia. A very important development in the treatment of life-threatening arrhythmias was the implantable defibrillator. Growing concern about failure to protect patients at risk for dying suddenly with antiarrhythmic drugs led to a rapid increase in their number. Cure by catheter ablation became possible for patients with different types of arrhythmias. Genetic analysis allowed the identification of different monogenic arrhythmic diseases. Several challenges remain: the epidemic of atrial fibrillation, arrhythmias in heart failure, and sudden death out-of-hospital. One-fifth of all deaths are sudden and unexpected. The important issue is how we are going to prevent these unnecessary deaths from occurring.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.