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Chapter 6: Wide QRS Complex Tachycardia

CASE 6–1A

A 33-year-old man with a history of recurrent palpitations and documented wide QRS tachycardia undergoes electrophysiologic evaluation. His 12-lead ECG is normal. The following was observed (figure). What is the most likely mechanism of tachycardia?

An ECG graph showing a normal sinus rhythm with consistent P, QRS, and T waves. As a 33-year-old man with a history of recurrent palpitations and documented wide QRS tachycardia, it’s notable that his 12-lead ECG appears normal. This can be a bit perplexing, as wide QRS tachycardia typically indicates a disruption in the normal electrical conduction of the heart, which should manifest as abnormal ECG findings. Wide QRS Tachycardia: This term implies that during episodes of tachycardia (a fast heart rate), the QRS complex on the ECG appears wider than normal. A normal QRS complex typically indicates that the electrical impulses in the heart are following their usual pathway. A wide QRS complex suggests that the electrical conduction is taking an abnormal route, possibly through the ventricles, which can be concerning. Normal 12-lead ECG: The 12-lead ECG is a standard diagnostic tool used to record the electrical activity of the heart from multiple angles or viewpoints. A “normal” ECG typically shows a consistent pattern of electrical activity, and it’s expected to be within certain parameters. However, in this case, despite the patient’s history of wide QRS tachycardia, the ECG doesn’t seem to show any immediate abnormalities.
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CASE 6–1B

An ECG graph showing a normal sinus rhythm with consistent P, QRS, and T waves. A 33-year-old man with a history of recurrent palpitations and documented wide QRS tachycardia presents an intriguing case, as his 12-lead ECG displays a seemingly normal sinus rhythm with consistent P, QRS, and T waves. This situation raises questions because wide QRS tachycardia usually signifies an aberration in the heart’s normal electrical conduction, which typically manifests as irregularities on an ECG. Let’s delve into this further. Wide QRS Tachycardia: This term indicates that, during episodes of tachycardia (a rapid heart rate), the QRS complex on the ECG appears broader than the norm. A standard QRS complex usually indicates that the heart’s electrical impulses are following their typical course. Conversely, a widened QRS complex implies that the electrical conduction is deviating from its usual path, potentially involving the ventricles, which can be a cause for concern. Normal 12-lead ECG: The 12-lead ECG is a conventional diagnostic tool utilized to record the heart’s electrical activity from various angles or perspectives. A “normal” ECG typically displays a consistent pattern of electrical activity, adhering to specific parameters. Nevertheless, in this particular instance, despite the patient’s history of wide QRS tachycardia, the ECG does not seem to exhibit any immediate irregularities.
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Explanation:

The initial four QRS complexes have an atypical right bundle branch block morphology suggesting either ventricular tachycardia (VT) or a preexcited tachycardia. There is 1:1 AV relationship with the earliest atrial electrogram in the septum. In such a situation, the differential diagnosis includes VT with 1:1 VA conduction, atrial tachycardia, or AV node reentry with anterograde conduction over an accessory pathway (AP), and antidromic tachycardia with anterograde conduction over an AP and retrograde conduction over either a second septal AP or the normal VA conduction system.

An atrial stimulus (S2) introduced during tachycardia at the MCS electrode site terminates tachycardia without conduction to the ventricle. This eliminates VT as a diagnosis. Termination with a relatively late-coupled PAC also favors a macro reentrant tachycardia with close access of the PAC to the excitable gap, that is, antidromic reentry in this case. Additional pacing maneuvers during the study proved the mechanism to be antidromic tachycardia with retrograde conduction over the normal VA conduction system.

The last two QRS complexes show no evidence of anterograde AP conduction. In fact, there is not even local evidence of preexcitation on the coronary sinus leads as demonstrated by a long conduction time between the local A and V (arrow). In a patient with antidromic reciprocating tachycardia (ART) there is typically some evidence of anterograde AP activation during sinus rhythm. This was a very unusual AP that only became manifest with multiple premature atrial extrastimuli that resulted in block over the AV node and a very long conduction time over the AP.

CASE 6–2A

A 46-year-old man with a history of recurrent palpitations and documented wide complex QRS tachycardia undergoes electrophysiologic study. His 12-lead ECG during tachycardia is shown in the figure. What are the diagnostic possibilities?

An ECG graph showing recurrent palpitations and wide complex QRS tachycardia. A 46-year-old man with a history of recurrent palpitations and wide complex QRS tachycardia undergoes an electrophysiologic study. The 12-lead ECG snapshot during tachycardia reveals his heart’s electrical activity during a rapid heart rate episode. The wide-complex QRS tachycardia indicates abnormal ventricular depolarization, suggesting irregular electrical conduction in the heart. The electrophysiology study helps assess this condition in detail.
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CASE 6–2B

An ECG graph showing recurrent palpitations and wide complex QRS tachycardia. An EP study of a 46-year-old man, with a history of recurrent palpitations and wide complex QRS tachycardia. Wide Complex QRS Tachycardia indicates a fast heart rate with an abnormally wide QRS complex on the ECG, suggesting irregular ventricular depolarization. An Electrophysiologic Study is a specialized procedure to examine the heart’s electrical system, using catheters to pinpoint electrical irregularities or disturbances within the heart’s rhythm.
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Explanation:

The tachycardia exhibits an atypical left bundle branch block morphology that is less likely aberrancy and more consistent with either VT or preexcited tachycardia. If it is a preexcited tachycardia, it is conducting anterogradely over a right free wall AP. There appears to be a negative P wave before each QRS complex in ECG leads II, III, and aVF. If this is VT, 1:1 retrograde conduction is most likely over a slow AV nodal pathway. ...

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