Wide Complex Tachycardias: Understanding this Complex Condition: Part 1 - Epidemiology and Electrophysiology.

R eview A rticle Wide Complex Tachycardias: Understanding this Complex Condition Part 1 – Epidemiology and Electrophysiology Gus M. Garmel, MD Stanford University School of Medicine / Kaiser Permanente, Santa Clara Submission history: Submitted August 18, 2007; Accepted November 26, 2007. Reprints available through open access at www.westjem.org [WestJEM. 2008;9:28-39.] INTRODUCTION Patients presenting to the emergency department (ED) with electrocardiograms (ECGs) indicating wide complex tachycardias (WCTs) are difficult to manage. Furthermore, these ECGs are often challenging to interpret. 1,2 Patients typically have ongoing chest discomfort, with or without symptoms of dyspnea, lightheadedness, nausea, and diaphoresis. Accurate interpretation of ECGs demonstrating WCTs assists clinicians who must treat patients presenting with this condition. Despite step-wise approaches and numerous criteria suggested to interpret WCTs, physicians (including cardiologists) often fail to agree on a surface electrocardiographic diagnosis. 3,4 Understanding the etiology of WCTs not only helps identify the cause of this condition, but also prevents its mismanagement, significantly reducing morbidity and mortality. 5,6,7 This is the first of two manuscripts designed to remove the “complex” from wide complex tachycardia identification (part 1) and management (part 2). Information is provided to help clinicians interpret ECGs demonstrating WCTs, including descriptions of the electro- and pathophysiology behind their development. Several examples of WCTs are provided with detailed interpretations. Diagnostic criteria from current literature and their relative accuracy are presented. In part 2, the most recent 2005 American Heart Association (AHA) guidelines for the treatment of WCTs are discussed, and management strategies for various WCTs are described given their underlying etiologies. Wide Complex Tachycardias (WCTs) are also known as Broad Complex or Wide QRS Complex Tachycardias. It is easiest to understand this nomenclature by considering these terms independently. Wide refers to a QRS complex duration (width) of greater than or equal to 0.12 seconds (120 msec), corresponding to three small boxes on the ECG paper. There are many reasons for QRS complexes to be widened (see Table 1). Any cause of a widened QRS complex can result in a sustained or nonsustained wide complex tachycardia if the rate is greater than 100 beats per minute. Etiologies Western Journal of Emergency Medicine of various WCTs are listed in Table 2, with schematic diagrams to better appreciate the conduction pathways and electrophysiology behind WCTs provided in Figure 1. The QRS Complex is the electrical stimulus on the ECG tracing as it passes from the AV node down the ventricular conduction system, terminating in the ventricular myocardial cells. 8 This definition, however, proves to be rather limited, as the electrical stimulus that results in the QRS complex may travel in either the forward or backward direction (anterograde or retrograde) using various pathways as part of the conduction circuit (orthodromic or antidromic). The direction of and pathway used by the electrical impulse greatly affects the duration of the QRS complex, which may impact the heart rate achieved. Tachycardia is generally defined as any heart rate or pulse greater than 100 beats per minute, whether or not this is sustained. Table 1. Etiologies of a wide QRS Complex *9 Nonspecific intraventricular conduction delay Aberrant ventricular conduction (Bundle Branch Block) Ventricular ectopic beat Ventricular excitation syndromes (Wolff-Parkinson-White Syndrome) Left ventricular hypertrophy Hyperkalemia Hypermagnesemia Pacemaker-generated beat Hypothermia Drug Toxicities (tricyclic antidepressants, cocaine, phenothiazines, lithium, diphenhydramine, or other drugs having sodium channel blockade or quinidine-like effects) * Any of these causes of a wide QRS complex may result in a WCT, given concomitant tachycardia. Volume IX, no . 1 : January 2008