Wide Complex Tachycardias - The Differential Diagnosis Remains Wide and Complex

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Abstract

In the nearly 30 years since Wellens et al. categorized most of the currently used electrocardiographic (ECG) criteria for distinguishing supraventricular tachycardia (SVT) with aberrant interventricular conduction from ventricular tachycardia (VT),1 there have been relatively infrequent and largely incremental enhancements to the art and science of making this distinction. In most published series, a correct diagnosis can be made using these criteria in up to 90% of cases. Despite this, few clinical situations evoke more anxiety in physicians and nurses than a patient with wide complex tachycardia (WCT). Often, residents and even staff physicians are seen poring over the WCT ECG and muttering under their breath, “I should know this!” Why does this situation continue to present such a clinical challenge? And what are the consequences of making an incorrect diagnosis?

Citation
US Cardiology, 2007;4(1):48-9

Pages

In the nearly 30 years since Wellens et al. categorized most of the currently used electrocardiographic (ECG) criteria for distinguishing supraventricular tachycardia (SVT) with aberrant interventricular conduction from ventricular tachycardia (VT),1 there have been relatively infrequent and largely incremental enhancements to the art and science of making this distinction. In most published series, a correct diagnosis can be made using these criteria in up to 90% of cases. Despite this, few clinical situations evoke more anxiety in physicians and nurses than a patient with wide complex tachycardia (WCT). Often, residents and even staff physicians are seen poring over the WCT ECG and muttering under their breath, “I should know this!” Why does this situation continue to present such a clinical challenge? And what are the consequences of making an incorrect diagnosis?
WCT has several potential causes, including VT; SVT with one of the following: aberrant interventricular conduction (SVT-A), atrioventricular (AV) conduction over an accessory pathway (Wolff-Parkinson-White), QRS widening due to drug effect/electrolyte abnormalities, or an abnormal bizarre baseline QRS (cardiomyopathy); or ventricular pacing. Although the proportion of cases falling into each category varies slightly depending on patient population, VT comprises about 67% of WCT in most series, with SVT-A accounting for another 25%. Thus, the most important distinction to make is between VT and SVT-A.

Current Methods

ECG differentiation of WCTs can be divided into two major areas: configurational (morphology of QRS) and relational (AV relationship during WCT). Configurational distinctions are based on QRS patterns that resemble aberrant conduction, and are thus more consistent with SVT-A, or do not resemble aberration patterns and are thus likely to be VT. Some of the more commonly used configurational criteria that are uncommon in SVT-A and thus strongly suggest VT are prolonged QRS duration (>140ms for right bundle branch block [RBBB] pattern QRS, >160ms for left bundle branch block [LBBB]); leftwards frontal plane axis (especially if between -90 and 180°); a fully concordant precordial R wave pattern (fully positive or fully negative); and specific patterns in leads V1 and V6 that are or are not compatible with aberrant conduction (see Figure 1).

Pages

References
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