What can cause a sudden increase in the QRS (QT interval in electrocardiography) interval?

From the Guidelines

A sudden increase in QRS interval can be caused by several factors, including sodium channel blocking drugs, severe hyperkalemia, bundle branch blocks, ventricular tachycardia, severe hypothermia, hypernatremia, and tricyclic antidepressant overdose. The most common causes of a sudden increase in QRS interval include:

• Sodium channel blocking drugs: Medications like Class IA and IC antiarrhythmics (e.g., quinidine, flecainide) can prolong the QRS interval, as noted in the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1.
• Severe hyperkalemia: High potassium levels can slow conduction through the ventricles, and abnormalities in potassium levels can cause changes on the ECG, as stated in the 2017 update to practice standards for electrocardiographic monitoring in hospital settings: a scientific statement from the American Heart Association 1.
• Bundle branch blocks: New-onset left or right bundle branch blocks can widen the QRS complex.
• Ventricular tachycardia: This can present with a wide QRS complex.
• Severe hypothermia: Low body temperature can slow cardiac conduction.
• Hypernatremia: Elevated sodium levels can affect cardiac conduction.
• Tricyclic antidepressant overdose: These medications can block sodium channels in high doses, as mentioned in the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1. If a sudden QRS prolongation is observed, immediate evaluation of the patient's medication list, recent electrolyte levels, and overall clinical status is crucial. In cases of drug-induced prolongation, discontinuation of the offending agent may be necessary. For electrolyte imbalances, prompt correction is essential. In the case of new conduction abnormalities or arrhythmias, further cardiac evaluation and potential intervention may be required. Understanding the underlying mechanism is important for appropriate management, as QRS prolongation reflects slowed ventricular depolarization, which can increase the risk of arrhythmias and sudden cardiac death if left untreated, highlighting the importance of prompt identification and addressing the cause, as supported by the 2017 update to practice standards for electrocardiographic monitoring in hospital settings: a scientific statement from the American Heart Association 1.

From the FDA Drug Label

Progressive widening of the QRS complex, prolonged Q-T and P-R intervals, lowering of the R and T waves, as well as increasing A-V block, may be seen with doses which are excessive for a given patient. If evidence of QRS widening of more than 25 percent or marked prolongation of the Q-T interval occurs, concern for overdosage is appropriate, and interruption of the PA infusion is advisable if a 50 percent increase occurs

A sudden increase in the QRS complex or QT interval can be caused by:

• Overdose of procainamide (PA)
• Excessive doses for a given patient
• High plasma levels of PA, especially above 10 mcg/mL 2
• Rapid administration of PA, causing high although transient plasma levels 2

From the Research

Causes of Sudden Increase in QRS Interval

• Sodium channel blockers, such as flecainide and disopyramide, can increase QRS duration in patients with Brugada syndrome 3
• Certain drugs can prolong the QT interval by blocking hERG-encoded potassium channels or modifying sodium channels, leading to a potential increase in QRS interval 4, 5
• Electrolyte abnormalities and genetic polymorphisms can also contribute to QT interval prolongation, which may be associated with an increase in QRS interval 4, 5
• Myocardium heterogeneity and drug-drug interactions can also play a role in QT interval prolongation and potentially affect the QRS interval 5
• Expression of expanded CUG-repeat RNA in the heart can lead to reduced sodium and potassium channel activity, resulting in QRS- and QT-interval prolongation 6

Factors Contributing to QT Interval Prolongation

• Use of QT prolonging drugs, which can act by blocking hERG-encoded potassium channels or modifying sodium channels 4, 5
• Genetic variants that potentiate the QT prolonging effect of drugs 4
• Electrolyte disturbances, such as hypokalemia or hypomagnesemia 5
• Myocardial ischemia or infarction, which can affect ventricular repolarization and increase the QT interval 7
• Channelopathies, such as long QT syndrome, which can interfere with the repolarization phase of the cardiac action potential 7