What is the cause of a wide QRS (quantitative electrocardiographic measurement) complex?

From the Guidelines

A wide QRS complex on an electrocardiogram (ECG) is defined as a QRS duration greater than 120 milliseconds and indicates abnormal ventricular depolarization, requiring immediate attention to determine the underlying cause and appropriate treatment. This finding can be caused by several conditions including bundle branch blocks (particularly right or left bundle branch block), ventricular rhythms (like ventricular tachycardia), hyperkalemia, sodium channel blocker toxicity, ventricular pacing, or pre-excitation syndromes such as Wolff-Parkinson-White syndrome 1. When encountering a wide QRS, it's essential to determine whether it represents a ventricular rhythm or a supraventricular rhythm with aberrant conduction, as this distinction affects treatment. For stable patients, a 12-lead ECG should be obtained and compared with previous tracings if available. Clinical context is crucial - associated symptoms, vital signs, and medical history help determine urgency.

Key Considerations

• Treatment depends on the underlying cause: antiarrhythmics for ventricular tachycardia, correction of electrolyte abnormalities for hyperkalemia, or specific interventions for other identified causes.
• If the patient is hemodynamically unstable with a wide QRS tachycardia, immediate cardioversion may be necessary regardless of the specific mechanism 1.
• For pharmacologic termination of a stable wide QRS-complex tachycardia, IV procainamide and/or sotalol are recommended, with amiodarone being preferred for patients with impaired left ventricular function or signs of heart failure 1.
• The management of atrial fibrillation and flutter is crucial, with DC cardioversion or pharmacologic conversion using IV ibutilide or flecainide being appropriate for termination of an irregular wide QRS-complex tachycardia 1.

Diagnostic Approach

• A 12-lead ECG is essential for evaluating the rhythm and determining the need for expert consultation.
• The QRS width criteria can help differentiate between VT and SVT with aberrant conduction, but are not foolproof 1.
• Clinical context, including associated symptoms, vital signs, and medical history, is vital for determining urgency and guiding treatment.

Treatment Priorities

• Morbidity, mortality, and quality of life are the primary outcomes to consider when managing a patient with a wide QRS complex.
• Treatment should be tailored to the underlying cause, with a focus on stabilizing the patient and preventing further complications.
• In cases where the diagnosis is uncertain, it is generally safer to treat the patient as if they have ventricular tachycardia, given the potential risks of misdiagnosis 1.

From the Research

Definition and Diagnosis of Wide QRS Complex

• Wide QRS complex tachycardia is a frequently encountered arrhythmia in the emergency department and presents a diagnostic challenge to the emergency physician 2.
• The diagnosis of ventricular tachycardia is supported by a history of prior myocardial infarction or congestive heart failure, physical examination showing cannon A-waves in the jugular venous pulsation or variable heart sounds, chest radiograph showing cardiomegaly or evidence of prior cardiac surgery, and characteristic ECG features 2.
• ECG criteria are used and algorithms developed to aid in differential diagnosis between ventricular tachycardia and supraventricular tachycardia conducted with aberrancy 3.

ECG Differential Diagnosis

• Numerous ECG features have been suggested as potential clues to the origin of wide QRS complex tachycardia, including ventricular rate, frontal axis, QRS complex width, and QRS morphology, as well as the presence of other characteristics such as atrioventricular dissociation and fusion/capture beats 4.
• A QRS morphology inconsistent with right or left bundle branch block can exclude a diagnosis of supraventricular tachycardia with aberrant ventricular conduction due to bundle branch block or ventricular preexcitation and establish a diagnosis of ventricular tachycardia 5.

Clinical Approach

• Patient age and history may assist in rhythm diagnosis, especially when coupled with electrocardiographic (ECG) evidence 4.
• When the rhythm diagnosis is in question, resuscitative therapy should be directed toward ventricular tachycardia 4.
• Electrophysiological study and RF ablation may be useful in the diagnosis and treatment of wide QRS complex tachycardia, especially in patients with a history of myocardial infarction and CABG 6.