Cardiac Conduction Disorders Covered on the Physician Assistant Exam

The Physician Assistant Exam will expect you to have an understanding of cardiac conduction disorders. Take this example. Rich has been around awhile and has taught both medical residents and physician assistants. Before that, he was a med student. Rich knows that when it comes to cardiology, two of the biggest causes of consternation, angst, and pain are answering physical-exam questions and identifying heart rhythms.

During an in-training exam in cardiology, he once saw one of his colleagues abruptly drop to the floor, assume the fetal position, and start sucking his thumb. Another person stood up and began screaming in an unintelligible language. This is complicated stuff.

Sometimes you’ll be the only person on the cardiology service with normal sinus rhythm (NSR). (Well, hopefully the cardiologist’s will be normal, too.) This is what a normal sinus rhythm looks like.

[Credit:     ©1997–2010 Intermountain Healthcare. All rights reserve
Credit:     ©1997–2010 Intermountain Healthcare. All rights reserved.

Atrial flutter and atrial fibrillation are probably the two most common arrhythmias you’ll deal with during your clinical career.

Atrial flutter

Atrial flutter is recognizable on an ECG or rhythm strip because of its saw-tooth appearance.

[Credit:     ©1997–2010 Intermountain Healthcare. All rights reserve
Credit:     ©1997–2010 Intermountain Healthcare. All rights reserved.

Here are two important points about atrial flutter:

  • Beta blockers and calcium channel blockers can be used for rate control, as can digoxin (Lanoxin), which also functions as an AV nodal blocker.

  • On physical examination, the rhythm can be irregular or regular, depending on the atrial flutter. For example, a 2:1 atrial flutter can sound very regular, whereas a 3:1 atrial flutter sounds very irregular.

Atrial fibrillation

Atrial fibrillation involves an atrium that is “fibrillating” rather than conducting. Imagine all sorts of atrial impulses being thrown at the AV node. In this situation, you’re called to see a patient with a tachycardia and you’re trying to figure out what’s causing the abnormal rhythm.

A-fib is probably the most common arrhythmia you’ll deal with in the hospital setting, even more so than atrial flutter. Here is an example of a rhythm strip showing atrial fibrillation.

[Credit:     ©2012 Science Photo Library—Custom Medical Stock Photo.
Credit:     ©2012 Science Photo Library—Custom Medical Stock Photo. All rights reserved.

A-fib can result from an underlying illness that stresses the heart, such as sepsis or pneumonia. You should check a TSH level in anyone with atrial fibrillation to evaluate for possible underlying hyperthyroidism as a cause of the arrhythmia.

Here are some important points about treating atrial fibrillation:

  • The initial treatment focuses on rate control. Just as with atrial flutter, calcium channel blockers like diltiazem (Cardizem) and beta blockers like metoprolol (Lopressor) as well as digoxin (Lanoxin) can be used for rate control.

  • If a person has been in atrial fibrillation for longer than 48 hours, or if you encounter a person with atrial fibrillation and its duration isn’t known, empiric anticoagulation with intravenous heparin with transition to oral warfarin (Coumadin) is mandatory to decrease the risk of embolic stroke.

  • A person with acute congestive heart failure and atrial fibrillation can be very hard to treat, because he or she has lost the 20 percent “atrial kick” to the left ventricle.

You can convert someone from atrial fibrillation to normal sinus rhythm (NSR) in a few different ways. In many cases, just slowing down the ventricular rate with the medications we’ve mentioned is enough. Other medications that are used to try to convert A-fib to normal sinus rhythm include amiodarone (Cordarone), sotalol (Betapace), and procainamide (Procan-SR).

Electrical cardioversion can also be done, although this requires the person to be anticoagulated for several weeks prior, and a transesophageal echocardiogram is usually done to make sure that there isn’t a clot in the area of the atrium known as the left atrial appendage.

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