3rd-Degree Atrioventricular Block

Abstract

Audience: This oral boards case is appropriate for emergency medicine residents and medical students on emergency medicine rotations.

Introduction/background: Third-degree heart block (also known as complete heart block) is a cardiovascular emergency that requires prompt recognition. Complete heart block is a type of atrioventricular (AV) block whereby no atrial impulses reach the ventricular conduction system. The most common etiology of AV block is ischemic heart disease, with up to 1 in 5 patients developing some type of conduction disturbance after an MI.1 Complete heart block is seen in 8% of patients post-MI.2 Other causes include myocarditis, infectious endocarditis, infiltrative cardiac disease, congenital AV blocks, non-ischemic cardiomyopathy, electrolyte disturbances, and drug side effects.3 In complete heart block, the heart rate is dependent on the location of the block and a functioning secondary pacemaker within the conduction system. Analysis of the EKG will determine the location of this escape rhythm. For escape rhythms originating at the AV node or high in the His-Purkinje system, the QRS complex will typically be narrow, and the ventricular rate typically in the 40-60 bpm range. For blocks with ventricular escape rhythms, the QRS will appear wide, with rates of 20-40 bpm. Patients presenting with 3rd-degree AVB with ventricular escape rhythms can destabilize. If no escape rhythm generates, patients develop asystole and cardiac arrest. Since 1 in 600 adults over the age of 65 will develop a form of supraventricular conduction abnormality each year, this disease process is important to identify and treat.4 Effective management includes accurate interpretation of a 12-lead EKG, assessment of hemodynamic stability and systemic perfusion, and time-sensitive pharmacologic or procedural intervention.

Educational objectives: At the end of this oral board session, examinees will: 1) demonstrate ability to obtain a complete medical history including detailed cardiac history, 2) demonstrate the ability to perform a detailed physical examination in a patient with cardiac complaints, 3) investigate the broad differential diagnoses which include acute coronary syndrome (ACS), electrolyte imbalances, pulmonary embolism, cerebrovascular accident, aortic dissection and arrhythmias, 4) obtain and interpret the cardiac monitor rhythm strip to identify complete heart block, 5) list the appropriate laboratory and imaging studies to differentiate arrhythmia from other diagnoses (complete blood count, comprehensive metabolic panel, magnesium level, EKG, troponin level, chest radiograph), 6) identify a patient with complete heart block and manage appropriately (administer IV atropine, attempt transcutaneous pacing, place a transvenous pacemaker, emergent consultation with interventional cardiology), 7) provide appropriate disposition to intensive care after consultation with interventional cardiologist.

Educational methods: This is a straight-forward case which was written to assess learners' ability to rapidly recognize an unstable cardiac rhythm and to subsequently treat and stabilize the patient. Oral board testing is used as a proxy for the emergency department (ED) and can assist with periodic assessment of resident performance while in the ED.We have found that oral board testing is a useful tool to assess residents' critical thinking while still applying pressure that is needed to pass the examination itself. Large groups of residents can be assessed in a short time period without needing to "wait" for a particular clinical condition to present to the ED.In this case, learners were assessed using a free online evaluation tool, ie, Google forms. Multiple questions were written for each critical action, and the Google form served as the online evaluation and repository. The critical actions of the case were then tied to Emergency Medicine Milestones, and the results were compiled for use during residency clinical competency evaluations. Residents were provided with immediate verbal feedback of their performance and were also given their electronic evaluations when requested.

Research methods: Learners and instructors were given the opportunity to provide electronic feedback after the case was completed to assess strengths and weaknesses, and subsequent modifications were made. Additionally, learners answered written multiple-choice questions after the case to assess for retention of the material.

Results: Senior learners found this to be a more enjoyable way to refresh their skills than direct lecture. Junior residents and students who encountered this clinical entity first in the oral board rather than in the ED, stated that they enjoyed the ability to "trial run" the case before being faced with an emergent and uncontrolled setting of the ED. Overall, the learners rated the case as 4.7 (1-5 Likert scale, 5 being excellent) after the mock oral board examination was completed.

Discussion: Students and residents who were assessed with a mock oral board session found this to be an improvement over traditional "lecture" and were pleased to have participated. The content is highly relevant to emergency medicine and the format forces learners to be actively engaged in review of the material. The case is a good model for the high stakes testing of written and oral board examinations, and is an effective way to assess a resident's ability to rapidly assess and manage a life-threatening condition in the ED.

Topics: Third-degree AV block, complete heart block, 3^rd-degree block, hypotension, syncope, bradycardia, cardiovascular emergency.

Image Source: Stillwaterising. Normal PA chest radiograph. In: Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Chest_Xray_PA_3-8-2010.png. Published March, 2008. Accessed October 1, 2021. Public Domain.

Image Citation: Author’s own image

Image Citation: Author’s own image

Image Citation: Author’s own image

Image Citation: Author’s own image