Understanding Third-Degree Heart Block: Dispelling the Misconceptions and Appropriate Management

QUESTION

You are treating a patient complaining of chest pain. Upon placing a 4 lead EKG you identify the patient to be profoundly bradycardic with a narrow QRS, and complete dissociation between the QRS and P waves. You inform your partner this patient is in a third-degree heart block, but your partner disagrees and states that third-degree heart blocks must have a wide QRS. Your partner proceeds to call a STEMI alert and asks you to start loading the patient. The QA process later investigated this call and discovered that your partner was incorrect about pretty much everything.

• Explain how a third-degree heart block can have a narrow QRS.
• Why do you think it’s such a common misconception that third-degree heart blocks can only be wide?
• Why is it inappropriate to call a STEMI alert on this patient?
• What should have been the appropriate treatment plan?
• Should this patient have been a “load and go?”

ANSWER

Understanding Third-Degree Heart Block: Dispelling the Misconceptions and Appropriate Management

Introduction

In the scenario presented, a patient complaining of chest pain is found to have profound bradycardia with a narrow QRS complex and complete dissociation between the QRS and P waves. While the provider correctly identifies this as a third-degree heart block, their partner disagrees, believing that third-degree heart blocks must have a wide QRS complex. This misconception leads to an inappropriate STEMI alert and potentially unnecessary interventions. This essay aims to clarify the possibility of a narrow QRS in third-degree heart block, explore the reasons behind this common misconception, discuss the inappropriateness of a STEMI alert in this case, propose the appropriate treatment plan, and evaluate the appropriateness of a “load and go” approach.

Third-Degree Heart Block with a Narrow QRS

Contrary to the misconception, third-degree heart blocks can indeed manifest with a narrow QRS complex. Third-degree (complete) heart block occurs when there is complete dissociation between the atria and ventricles, resulting in the atria and ventricles beating independently. In some cases, the escape rhythm originating from the ventricles may have a narrow QRS complex, resembling a normal electrical conduction pattern. This occurs when the block is located in the atrioventricular (AV) node or the bundle of His, allowing the ventricular escape rhythm to be conducted through the normal conduction pathways.

Misconception Origins

The misconception that third-degree heart blocks must have a wide QRS complex may arise from the association between wide QRS complexes and infranodal blocks. Infranodal blocks, including bundle branch blocks, typically result in wide QRS complexes. However, in cases where the block occurs above the His-Purkinje system, such as in the AV node or the bundle of His itself, the escape rhythm can maintain a narrow QRS complex.

Inappropriateness of STEMI Alert

Calling a STEMI alert based solely on the presence of a narrow QRS complex in this patient with third-degree heart block is inappropriate. ST-elevation myocardial infarction (STEMI) alerts are intended for identifying patients experiencing acute coronary syndromes characterized by ST-segment elevation on the EKG. Third-degree heart block, regardless of QRS width, does not fulfill the diagnostic criteria for a STEMI. Thus, the STEMI alert may result in unnecessary resource utilization and potential delays in appropriate patient management.

Appropriate Treatment Plan

In the scenario described, the appropriate treatment plan for the patient with third-degree heart block and chest pain would be to address the bradycardia and consider the underlying cause of the block. As the patient is symptomatic, immediate interventions should be initiated. These may include providing supplemental oxygen, establishing intravenous access, and considering atropine administration to increase heart rate. However, it is important to note that transcutaneous pacing or transvenous pacing should be the definitive treatment for unstable patients or those who do not respond to initial interventions.

Appropriateness of “Load and Go”

In this case, a “load and go” approach, which typically involves rapidly transporting patients to a cardiac catheterization laboratory for emergent intervention, would not be appropriate. As the patient’s presentation is primarily due to bradycardia and third-degree heart block, the focus should be on stabilizing the patient’s rhythm and addressing the underlying cause. Immediate interventions, such as transcutaneous pacing if necessary, should be initiated at the bedside to stabilize the patient before considering further interventions or transportation.

Conclusion

Understanding the various presentations of third-degree heart block, including the possibility of a narrow QRS complex, is crucial for accurate diagnosis and appropriate management. Dispelling the common misconception that third-degree heart blocks must be associated with a wide QRS complex is essential to prevent inappropriate interventions and improve patient outcomes. Providers should rely on established diagnostic criteria and guidelines to determine the appropriate treatment plan, ensuring that patients receive the most effective and timely care.