Wide QRS Complex Tachycardia

The heart has a complex electrical conduction system. This system is interwoven in the myocardium, which allows the heart to beat at its own rhythm and creates what’s called a pulse (one of six important vital signs). The heart has what is called a pacemaker, and its function is to determine how fast the heart will beat. It is because of this intricate electrical system that allows all cardiac cells to beat (i.e., depolarize) in unison. A heartbeat (i.e., pulse) can be classified as either regular versus irregular, fast versus slow, etc. When a person’s pulse falls out of what is considered “normal,” then we say this individual has an arrhythmia. Electrocardiograms (a.k.a. EKGs or ECGs) are used to help evaluate aberrancies in a patient’s heart rhythm and pulse. Arrhythmias can be classified by either how fast the heart is beating, i.e., rate (tachycardia, bradycardia), the regularity of the heartbeat (regular, irregularly regular, or irregularly irregular), and finally by the width of the QRS complex (narrow, wide). This article will be discussing a specific group of arrhythmias – Wide QRS complex tachycardia (WTC). It is important to go over some basic definitions describing what WCTs are, what causes them, how to diagnose them, and how to manage/treat them. Tachycardia refers to a heart rate that is >100 beats per minute. The QRS complex represents ventricular depolarization on the EKG. To briefly explain some cardiac anatomy, a normal heartbeat is generated by an electrical stimulus that originates in the sino-atrial (SA) node. This stimulus then travels from the SA node to the atrioventricular (AV) node. The normal conduction pathway for this electrical stimulus (which represents the QRS) is from the AV node down the bundle of His, Purkinje fibers, and then into the ventricular myocardium which causes them to contract (depolarize). The pathway just described is considered anterograde and orthodromic because it follows the normal conduction circuit. When there are structural changes of the heart that can create alternative conduction pathways, this can cause the electrical stimulus to go in reverse and would then be called retrograde and antidromic. Depending on which pathway the electrical stimulus takes, it will affect how the QRS complex will be visualized on the EKG. A normal QRS should be less than 0.12 seconds (120 milliseconds), therefore a wide QRS will be greater than or equal to 0.12 seconds. To put it all together, a WCT is considered a cardiac dysrhythmia that is > 100 beats per minute, wide QRS (> 0.12 seconds), and can have either a regular or irregular rhythm. This article will be covering WCT’s etiologies, epidemiology, evaluation, management, treatment, prognosis, complications, and prevention. Of note, in an emergency situation where the patient is not clinically stable, it is important for physicians to understand that correctly interpreting the type of WCT in this setting should not be their primary concern. Rapidly and accurately diagnosing WCT still remains a problem because there are numerous algorithms and complicated criteria that can be difficult to remember in an emergency setting. The most important thing to do in such a situation is to stabilize the patient and just diagnose the WCT secondary to unknown origin or etiology.