Teachable Moments in ECG. The Mighty Duck Strategy: Remaining Calm in the Face of Wide Complex Tachycardia

Introduction 

Wide QRS complex tachycardias are, to say the least, “nightmare cases” for the physician manning the emergency room or intensive care unit. In majority of these cases, and especially in emergency situations, the dictum is to treat and manage as ventricular tachycardia (VT), unless proven otherwise. Since VT is a dreaded cardiac arrhythmia that is potentially fatal and more importantly associated with worse outcomes in most cases, this condition usually poses challenging and tense situations for the healthcare team. One needs to immediately assess the patient, correctly decipher the tracing and decide whether to intervene immediately or not. These cases can easily present with a stormy course, adding more anxiety and tension to an already stressful situation. 

Description of the Case 

A 55-year-old man was brought to the emergency department because of shortness of breath and palpitations. On assessment, vital signs showed: blood pressure 100/70 mmHg, heart rate 130 beats per minute (bpm) regular, respiratory rate 26 per minute and temperature 36.5 degrees Celsius with an oxygen saturation of 93%. An electrocardiogram (ECG) tracing was taken (Figure 1). 

Figure 1. ECG rhythm strip of the case showing tachycardia with a rate of 125 bpm.

Duck

It is in this crisis when the physician must adopt the duck mentality. This is a concept derived from the motivational phrase and quote from author Jason Braude: “When you are in a crisis, in a tight situation, in a struggle, in difficult moments, just be like a duck. Remain calm on the surface. But paddle like crazy underneath.”[1]

Ducks epitomize calmness and composure. They appear quiet on the surface while working energetically underneath the water, paddling with a lot of vigor in the face of a storm. When faced with wide complex tachycardia, we must appear calm, but “do the necessary stuff underwater”. This duck mentality is something worth adapting when we deal with challenging situations in medicine, not just tachycardias. 

Decipher the Tracing 

In a majority of clinical settings, complete analysis and full interpretation of the ECG tracings is usually done in retrospect, after the patient has been treated and stabilized. Within the ECG reading room of the diagnostic cardiovascular unit or Heart Station, the examination of these tracings become an engaging academic exercise between the student and expert, providing for some “teachable moments” that may be applied even up to the subspecialists’ level. 

Define

Wide QRS complex tachycardias or wide complex tachycardias are defined as conditions with a heart rate of more than 100 bpm and a QRS duration of more than 0.12 seconds (Figure 2).[2]

Figure 2. Wide QRS complex tachycardia is characterized by a rate of more than 100 bpm, with a QRS duration of more than 0.12 seconds or 120 ms (more than three small squares in the standard ECG strip) 

VT is a form of wide complex tachycardia which originates in the region below the Bundle of His in the cardiac conduction system. In essence, it is a tachycardia originating from the ventricular muscle. By ECG criteria, it is defined as three or more consecutive premature ventricular complexes (PVCs) with a rate of more than 100 bpm, with the QRS duration commonly more than 0.12 seconds or 120 ms in duration (Figure 3).[2]

Supraventricular tachycardia (SVT) is a tachycardia which originates above the Bundle of His, and in essence originates or involves the atrial tissue or AV node. It presents usually with a narrow QRS complex.[3] Sometimes, an SVT can conduct with an aberrancy or aberrant conduction in the form of a bundle branch block (BBB) or intraventricular conduction delay (Figure 3), or in situations involving an antegradely conducting bypass tract or accessory pathway, leading to a wide complex pattern on the ECG.[2]

Figure 3. A. In a normal sinus beat, the impulse originates from the sinus node, leading to atrial depolarization, then conducts down the AV node and His-Purkinje system leading to ventricular depolarization and a normal narrow QRS complex. B. A ventricular complex originates from the ventricular myocardium leading to depolarization of the ventricle of origin first before the impulse conducts to the His-Purkinje system in the interventricular septum and to the opposite ventricle through cell-to-cell depolarization, leading to a wide QRS complex. C. A supraventricular beat that conducts with aberration or aberrancy originates from a focus in the atrium, which conducts to the AV node and finds one part of the conducting system (usually the right bundle branch) refractory and not able to receive the impulse. It therefore conducts down the opposite bundle branch leading to depolarization of one ventricle before the wavefront of depolarization conducts through to the other ventricle via cellto-cell depolarization, leading to a wide QRS complex. 

Differentials

Not all wide complex tachycardias are VT, but a majority are. By statistics, approximately 80% of wide complex tachycardias are VT, while 20% are caused by other arrhythmias.[2]

When faced with this tracing, the following differential diagnosis should come in mind:

1. Sinus tachycardia with aberrant conduction (BBB), 

2. SVT with aberrant conduction (BBB), 

3. Pre-excited tachycardia (sinus tachycardia with preexcitation or pre-excited atrial fibrillation seen in patients with Wolff-Parkinson-White syndrome), 

4. SVT with antegrade conduction over accessory pathway (antidromic SVT), 

5. Pacemaker-mediated tachycardia, and 

6. VT.[4]

The first five are usually benign arrhythmias, except for pre-excited atrial fibrillation (Wolff-Parkinson-White syndrome), which can be fatal and potentially degenerate into ventricular fibrillation. Pacemaker-mediated tachycardia can happen in patients with an implanted dual chamber permanent pacemaker. As a rule, VT is a dangerous arrhythmia although there are some exceptions such as idiopathic VT, which are benign tachycardias in patients with structurally normal hearts. In most cases, VT requires immediate intervention as it can lead to hemodynamic instability and degenerate into ventricular fibrillation, resulting in cardiac arrest. Furthermore, the treatment of VT is different for other conditions in this list. Therefore, the correct interpretation of wide complex tachycardias is key to correct management. 

Defibrillate (if Pulseless) 

If a patient with wide complex tachycardia presents with no pulse, no blood pressure and no breathing (in cardiac arrest), a diagnosis of pulseless VT is clinched and immediate defibrillation must be done followed by chest compression and resuscitative measures, similar to the treatment of ventricular fibrillation.[5]

Document

In instances when a patient with wide complex tachycardia presents with pulse but in a hemodynamically unstable condition (hypotension, altered sensorium, dizziness, syncope, signs of heart failure), VT is the most likely diagnosis and immediate intervention must be done in the form of synchronized cardioversion.[5] In other cases when the patient is hemodynamically stable, a full 12-lead ECG should be taken. It is advised and highly recommended that a full 12-lead ECG also be taken quickly for the first situation (unstable wide complex tachycardia) before intervening. A 12-lead tracing will give a clearer picture of arrhythmia and allows for more extensive analysis of the morphologic patterns in retrospect. It is also valuable for later planning for definitive interventions such as ablation. Hence, if the patient is stable, always document with a 12-lead ECG before intervening to convert the tachycardia. Figure 4 shows the full 12-lead ECG of the patient described.