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Heart blocks: Pathology review

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Pathology

Cardiovascular system

Vascular disorders
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Cardiac arrhythmias
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Cardiovascular system pathology review

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Heart blocks: Pathology review

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Questions

USMLE® Step 1 style questions USMLE

3 questions
Preview

A 71-year-old man presents to the emergency department with sudden onset chest pain. He was sitting at home watching television when he noticed the pain, characterized as a sharp pressure-like sensation in the left side of his chest. He is having difficulty catching his breath. Medical history is significant for hypertension, COPD, chronic kidney disease, and coronary artery disease. He takes amlodipine, lisinopril, aspirin, salmeterol, and albuterol. His father died from a heart attack at age 50. He smokes one pack of cigarettes per day and drinks occasionally. His temperature is 37.2°C (99°F), pulse is 105/min, respirations are 23/min, blood pressure is 90/60 mmHg, and oxygen saturation is 90% on room air. He appears pale and diaphoretic. Physical exam shows a holosystolic murmur at the left mid sternal border that increases with supine leg raise. Lung examination is normal. An ECG is obtained and shows the following:  



 Reproduced from: Wikimedia Commons

Which of the following is the most likely cause of this patient’s symptoms?  

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Transcript

Mikey is a 22 year old male college student from Vermont who was sent to the emergency department after passing out.

His vital signs show a heart rate of 40 beats per minute and a blood pressure of 90/50. On examination, there is an erythematous circular rash with central clearing.

His friends mention they recently went on a hiking trip. His ECG is as follows.

Natasha is a 60 year old female with chronic hypertension, diabetes, and peripheral vascular disease who comes to the emergency room complaining of sudden-onset, squeezing retrosternal chest pain accompanied by shortness of breath and sweating.

Her ECG is as follows. On laboratory evaluation, her troponin levels are significantly elevated.

Alright, so the normal electrical activity of the heart starts in the sinoatrial or SA node located near the opening of the superior vena cava into the right atrium.

Electrical activity is then conducted through the atrium to the atrioventricular, or AV node, after which it goes through the Bundle of His, then the right and left branches of the Bundle, and finally through the Purkinje fibers which deliver the current to the right and left ventricles.

Now, normally there is delay in conduction at the AV node and the Bundle of His, which gives some time for ventricular filling before the ventricle contracts.

A “heart block”, or AV block, occurs when conduction is delayed for too long at the AV node or the bundle of His. Also, electrical activity may be blocked at the level of the bundle branches, which are called bundle branch blocks.

Okay, on the ECG, the normal delay in the AV node is represented by the PR interval, which is normally less than 5 small boxes, or 200 milliseconds.

There are three main types of AV block.

1st degree AV block is technically not really a block, it’s more of a delay.

Every single atrial impulse eventually makes it to the ventricles.

The high yield concept here is that the only abnormality is a prolonged PR interval, and it’s usually asymptomatic, so it does not require treatment.

2nd degree AV block has two subtypes: Mobitz 1, and Mobitz 2. In Mobitz 1, each atrial impulse encounters a longer and longer delay until one of them does no