A Quick Recap and the WCT Umbrella

To recap, in Chapter 27, Narrow-Complex Supraventricular Tachycardia, we started by looking at the supraventricular tachycardias (SVTs) in general. We saw how one of the major decision trees in the evaluation of the SVTs was to assign them into one of two groups based on the width of the QRS intervals:

1. An SVT with a QRS interval that is narrower than 0.12 seconds is considered a narrow-complex SVT.
2. An SVT that is wider than or equal to 0.12 seconds is considered a wide-complex SVT.

Note that both of these contain the word supraventricular to identify that they either originate in or need parts of the sinus node, the atrial myocardium, or the atrioventricular (AV) node to maintain their reentry circuits.

Are there any “pure” wide-complex SVTs? Think about that before you answer. If you think about it, there are no “pure” ones. What typically occurs is that the narrow-complex tachycardias become wide because they develop some form of aberrant conduction due to either rapid rates or external forces. The bottom line is that wide-complex SVTs are actually supraventricular tachycardias with aberrancy (abbreviated SVT-A in the singular form and SVTs-A in the plural).

The wide-complex SVTs are composed of tachycardic rhythms that demonstrate various levels of aberrant conduction (SVT-A or SVTs-A). Mechanisms causing the aberrancies include preexisting bundle branch block (BBB) or intraventricular conduction delays (IVCDs), rate-related changes, metabolic complications, drugs (especially the antiarrhythmic drugs), physiologic processes, paced rhythms, and the use of accessory pathways. We will discuss aberrancies further later in the chapter.

In general, the hemodynamic status of the patient with an SVT-A depends on the rate of the rhythm and the existence of other comorbidities. Most SVTs-A are generally well tolerated unless they are complicated by structural heart defects or other physiologic processes.

Now, having looked at the wide-complex supraventricular tachycardias, let’s turn our attention to another class of rhythms that also give rise to wide QRS complexes: the ventricular tachycardias (VTachs). From a clinical standpoint, VTach is one of deadliest arrhythmias we will face (as we saw in Chapter 32, Ventricular Tachycardia).

So, when looking at a rhythm that demonstrates wide QRS complexes, we are faced with two possibilities: the VTachs or the SVTs-A. Together, these two groups unite to create a new umbrella term known as the wide-complex tachycardias (WCTs; Figure 34-1). This subtle difference between wide-complex SVTs and the WCTs is often lost on beginner and intermediate students, who consider them to be interchangeable. The two groups differ in their site of origin, mechanism of disease, and clinical courses. The presence of VTach in the list of WCTs completely alters the clinical, diagnostic, and therapeutic approaches we must take to fully understand, evaluate, and treat this deadly group of arrhythmias. Differentiating between these two classes is extremely challenging and represents the primary clinical focus of clinicians as they face these patients.

Figure 34-1 Wide-complex tachycardias is an umbrella term encompassing both ventricular tachycardias and the supraventricular tachycardias with aberrancy.

© Jones & Bartlett Learning.

Description

To understand the clinical impact of this particular umbrella term, let’s start off with an analogy in which the term cars represents the WCTs. On its own, car doesn’t convey tons of information except that the vehicle has four wheels and is a means of transportation. Let’s now break down cars into the various brands: Chevrolet, Ford, BMW, etc. We can isolate them further by type—coupe, sedan, SUV—and then by model. Eventually, you would be able to identify a particular coupe as a “1969 Chevrolet Camaro SS, Kelly green with black interior and . . .” (that would be one very specific arrhythmia!). Or you may identify a particular SUV as a Hummer, which can run over you as if you were a speed bump, leaving you dead and making the rest of this analogy pointless (hence, VTach). Get the picture?

So, what’s the importance of this umbrella term? The various governing and certifying bodies have created a treatment strategy that can safely be used to treat WCTs as a whole. This simplification provides a greater safety profile for patients, affording clinicians of all levels of training and experience a more unified approach to treatment that does not require absolute certainty of an exact diagnosis. That said, we cannot emphasize strongly enough that if you are faced with an untypable WCT, you should always treat it as if it were a VTach. As mentioned many times before, statistics would be on your side, since over 80% of the WCTs are VTach.^1-5

Keep in mind that you should not use this treatment approach as an excuse to not study the individual rhythms. The ultimate gold standard remains to focus treatment on an exact diagnosis. However, as we shall soon see, this level of exactitude is not always possible when confronting the WCTs.