Sinus Bradycardia: How low is too low?

12 Mar

RAGING HYPOTHETICAL:

Your next patient is a 22 year old healthy male presents to the ED with chest pain c/w pleurisy.

EKG shows benign early repolarization and sinus bradycardia to ~45 bpm. Labs and CXR are normal.

While in the ED, the patient is on cardiac monitor and his resting heart rate decreases to 38 bpm.  He is asymptomatic.

What now?

 

PRINCIPLES TO CONSIDER:

1. Any symptoms?

 Any syncope, lightheadedness during episodes, bradycardia-tachycardia episodes = symptomatic bradycardia, which will need more in depth evaluation.

 

2. Get an EKG

 Make sure the rhythm is in fact sinus and see if there is any evidence of heart block, this is a different story- a few of these patients go on to require pacers.

 

3. Overall clinical picture

 Is the patient a young ultra-marathon runner? What meds are they on?

DDxof pathologic bradycardia is basically intrinsic heart (infarction, infection…) or extrinsic (pharmacologic cause, electrolyte abnormalities, hypothermia, hypothyroidism, increased ICP, increased vagal tone).

 

4. If you are still concerned after a good Hx, PE, and EKG, you can consider basic labs with a TSH.

 

5. Does the patient’s HR increase with exercise?

It obviously should. Patient’s without an appropriate response to exercise will require further work-up.

 

The Bottom Line:

* Most of the sources I looked at say a sinus rate of <40 bpm while awake without physical conditioning is generally abnormal

 

* Dr. DiMarco’s paper says asymptomatic episodes of sinus bradycardia (with heart rates as low as 30 bpm) and sinus pauses up to 3 seconds should be considered within the normal range (with the caveats mentioned above).

 

* I would say if you are still unsure or uncomfortable or find anything concerning after going through the above points, talk with Cardiology.

 

Submitted by H. Groth.

 

References: Mangrum, J. Michael and DiMarco, John P. “The Evaluation and Management of Bradycardia” New England

Journal of Medicine 2000; 342:703-709; Harrison’s Practice; MD Consult; Up-To-Date.com; picture

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