Ventricular Tachycardia (VT): This is often the first consideration for a wide QRS complex because it is a life-threatening condition that requires immediate attention. VT is characterized by a series of three or more consecutive, abnormally wide complexes at a rate typically exceeding 100 beats per minute.

Bundle Branch Blocks: Both left and right bundle branch blocks can cause a wide QRS complex. These conditions involve a delay or obstruction in the electrical conduction pathways of the heart, leading to asynchronous ventricular contraction.
Premature Ventricular Contractions (PVCs): While typically not sustained, PVCs can present with a wide QRS complex due to their ectopic origin outside the normal conduction system.
Wolff-Parkinson-White (WPW) Syndrome: This condition involves an accessory electrical pathway between the atria and ventricles, which can cause the ventricles to contract prematurely, leading to a wide QRS complex in certain situations.

Hyperkalemia: Elevated potassium levels can cause widening of the QRS complex due to its effects on cardiac membrane potential and conduction. This condition is potentially life-threatening and requires immediate intervention.
Torsades de Pointes: A specific type of polymorphic ventricular tachycardia that can be triggered by various factors, including certain medications and electrolyte imbalances. It is characterized by a "twisting" pattern on the ECG and can degenerate into ventricular fibrillation.
Cardiac Ischemia/Infarction: While not always presenting with a wide QRS complex, myocardial ischemia or infarction can lead to conduction abnormalities, including bundle branch blocks or VT, especially if the ischemia involves the conduction system.

Hypothermia: Severe hypothermia can affect the heart's electrical activity, potentially leading to a wide QRS complex among other ECG abnormalities.
Toxicity from Certain Medications or Substances: Certain medications (e.g., class I anti-arrhythmics, tricyclic antidepressants) and substances (e.g., cocaine) can cause widening of the QRS complex due to their effects on cardiac conduction.
Cardiac Sarcoidosis: A condition where granulomatous inflammation affects the heart, potentially leading to conduction abnormalities, including wide QRS complexes due to involvement of the ventricular myocardium or conduction system.
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): A rare heart condition characterized by replacement of the muscle tissue in the right ventricle by fatty tissue, which can lead to abnormal heart rhythms, including those with wide QRS complexes.