Which coronary artery occlusion is most likely to cause transient complete heart block with a narrow QRS complex in a patient with chest heaviness, diaphoresis, and shortness of breath?

From the Guidelines

The occlusion of the right coronary artery (RCA) is most likely to cause transient complete heart block with a narrow QRS complex in a patient presenting with chest heaviness, diaphoresis, and shortness of breath. This occurs because the RCA supplies blood to the atrioventricular (AV) node in approximately 90% of people. When the RCA becomes occluded during an acute myocardial infarction, the AV node loses its blood supply, resulting in impaired electrical conduction between the atria and ventricles, manifesting as complete heart block. The narrow QRS complex indicates that the block is occurring at the AV node level while the ventricular conduction system remains intact. The patient's symptoms of chest heaviness, diaphoresis, and shortness of breath are classic presentations of acute coronary syndrome. This type of heart block is often transient because collateral circulation may develop, or reperfusion therapy may restore blood flow to the AV node. Prompt recognition and treatment with reperfusion strategies such as percutaneous coronary intervention or thrombolytic therapy is essential, along with temporary pacing if the patient is hemodynamically unstable, as supported by guidelines such as those from the European Society of Cardiology 1.

Key points to consider in this scenario include:

• The RCA's role in supplying the AV node and the potential for AV block in the event of occlusion
• The presentation of acute coronary syndrome and the importance of prompt recognition and treatment
• The potential for transient complete heart block with a narrow QRS complex and the need for temporary pacing in hemodynamically unstable patients
• The role of reperfusion therapy in restoring blood flow to the AV node and improving outcomes

It's also important to note that while other coronary arteries, such as the left anterior descending or left circumflex, can also be involved in acute coronary syndromes, the RCA is most commonly associated with AV block due to its blood supply to the AV node. Therefore, in the context of a patient presenting with chest heaviness, diaphoresis, and shortness of breath, and considering the potential for transient complete heart block with a narrow QRS complex, the right coronary artery is the most likely culprit.

From the Research

Coronary Artery Occlusion and Transient Complete Heart Block

The patient's symptoms of chest heaviness, diaphoresis, and shortness of breath suggest an acute coronary syndrome. Considering the options provided:

• Left Anterior Descending (LAD) Artery: Occlusion of the LAD artery can lead to anterior myocardial infarction and potentially cause transient complete heart block, especially if the occlusion involves the first septal perforator, as seen in a case report 2. This is because the first septal perforator supplies blood to the conduction system of the heart.
• Left Circumflex Artery: While occlusion of the left circumflex artery can cause myocardial infarction, it is less commonly associated with transient complete heart block compared to occlusions involving the LAD or right coronary artery.
• Left Coronary Artery: The term "left coronary artery" refers to the main trunk that divides into the LAD and left circumflex arteries. Occlusion at this level would have widespread effects but is not specifically identified as a common cause of transient complete heart block in the provided studies.
• Right Coronary Artery (RCA): The RCA supplies blood to the posterior descending artery (PDA) in most individuals and is crucial for the blood supply to the atrioventricular (AV) node and the bundle of His. Occlusion of the RCA can lead to inferior myocardial infarction and is known to cause transient complete heart block, particularly if the block involves the AV node 3, 4.

Key Findings

• The LAD artery's occlusion, particularly involving the first septal perforator, can lead to transient complete heart block 2.
• The RCA's occlusion is associated with a risk of transient complete heart block due to its supply to the AV node and the bundle of His.
• The width of the QRS complex in complete heart block can vary; a narrow QRS complex suggests the block is at the AV nodal level rather than a bundle branch block.

Most Likely Cause

Given the information and the need for a narrow QRS complex in transient complete heart block, the Right Coronary Artery (RCA) is the most likely cause. This is because the RCA supplies the AV node, and its occlusion can lead to AV nodal block, which typically presents with a narrow QRS complex unless there is a pre-existing bundle branch block. However, the provided case reports and studies do not directly address the scenario of transient complete heart block with a narrow QRS complex in the context of chest heaviness, diaphoresis, and shortness of breath specifically due to RCA occlusion. The closest association from the provided evidence is the involvement of the RCA in causing conduction disturbances 3, 4.