Slide 1: 85-year-old male, history of atrial fibrillation, CAD status post PCI presents with syncope. What’s the diagnosis?

Slide 2: The atrial rhythm is atrial fibrillation. What about the ventricular rhythm? EKG shown with arrows pointing to the fibrillation waves and no discernable P-waves.

At first glance, the rhythm looks like AFib with slow ventricular response (<60 bpm), however, AFib should appear irregularly irregular. In AFib with bradycardia (<60 bpm), it's important to closely examine R-R intervals to look for periods of regularity that may suggest processes such as complete heart block. Slide 3: Atrial fibrillation can be classified by ventricular rate. Slow ventricular response is less than 60 bpm. Normal ventricular response is 60 to 100 bpm. Rapid ventricular response is greater than 100 bpm. Note: Look out for reversible causes of AFib with slow ventricular response. Some common causes include: ischemia, electrolyte abnormalities, AV nodal blocking agents, hypothyroidism, hypothermia. Caution: In AFib with slow ventricular response, make sure you're not missing complete heart block. Each QRS complex reflects conduction through the AV node to the ventricles, impacted by many intrinsic and extrinsic factors (ie. hormones, medications, etc.) affecting the AV node refractory period, ultimately determining the ventricular rate. Slide 4: Notice the regular R-R intervals. EKG showing R-R interval of approximately 1.48 seconds. AFib with regular R-R intervals suggests disconnect between the atria and ventricles: complete heart block. Complete heart block escape rhythms include junctional and ventricular. Junctional escape rhythm has QRS unchanged from baseline and is typically narrow QRS. Ventricular escape rhythm has a wider QRS that differs from baseline and different/abnormal axis. Slide 5: What's going on in the heart? Slow AFib. AV node refractory period allows some irregular fibrillatory impulses to conduct along the appropriate conduction pathway through the AV node down to the ventricles, resulting in irregular beats.Graphic showing atrial fibrillatory impulses. AV node appropriately conducts impulses. Complete heart block. With atrial impulses blocked, infra-nodal automaticity (junctional or ventricular) generates regular rhythms. Graphic showing heart block inhibits atrial conduction to the ventricles. Intrinsic infra-nodal automaticity. Slide 6: Take home points: look for regular R-R intervals in AFib with bradycardia to rule out complete heart block. AFib with complete heart block is an indication to stop rate control agents and call EP for urgent pacemaker placement, as well as temporary pacing until then. In AFib with slow ventricular response, a pacemaker may be indicated once the patient is off rate control agents and still symptomatic.