The newest AHA guidelines address the evaluation and management of bradycardia and conduction disorders. This includes sinus node dysfunction, AV blocks, and bundle branch blocks. Here’s what you need to know as an emergency physician.
Why does this matter?
We frequently see patients who present with bradycardia, either symptomatic or asymptomatic. We need to be experts in managing this.
Here’s what you need to know
Sinus node dysfunction (formerly called sick sinus syndrome) is a broad term that encompasses a variety of conditions:
- Sinus bradycardia with HR < 50 bpm
- Ectopic atrial bradycardia with HR < 50 bpm
- Sinus pause > 3 seconds
- Sinus arrest
- Chronotropic incompetence: HR does not increase appropriately during physical exertion.
- Tachy/brady syndrome: Atrial tachycardia (usually A fib) is most commonly followed by sinus pauses at the termination of the tachycardia. This transition often leads to syncope or near syncope.
- Isorhythmic dissociation
- Sinus node dysfunction must occur in the presence of symptoms. In other words, Lance Armstrong’s resting heart rate of 32 bpm is not sinus node dysfunction.
Workup and management
In all situations, first consider reversible causes of SND or blocks, especially hyperkalemia or hypokalemia. Those with reversible causes generally don’t need a permanent pacemaker. See Table 7 from the guideline.
Then consider atropine with a few words of caution:
- Paradoxical bradycardia: You must give at least 0.5mg of atropine. Giving less may cause bradycardia.
- Avoid in heart transplant patients: Atropine causes heart block or sinus arrest in up to 20% of patients. Bradycardia in heart transplant patients is often defined as < 70-80 bpm.
- Is the QRS narrow or wide? AV block with a narrow QRS generally indicates the block is at the AV node and conducting through the His-Purkinje system normally. Therefore, atropine will help. If the AV block is infra-nodal, atropine does not help and has even been reported to worsen conduction delays. Try a catecholamine instead (or just pace them) unless there is concern for possible cardiac ischemia as a cause of the bradycardia.
If hemodynamically unstable or with severe symptoms, pace the patient either transcutaneously or transvenously.
Consider aminophylline, which inhibits the suppressive effects of adenosine on the SA node, in 3 situations:
- Acute inferior MI with 2nd or 3rd degree AV block: 250mg IV bolus
- Heart transplant: 6mg/kg in 100-200 mL of IV fluid over 20-30 minutes
- Spinal cord injury: Often refractory to atropine and catecholamines due to de-innervation. Use the same dose as for heart transplant.
Who gets a permanent pacemaker?
- Patients with irreversible, symptomatic sinus node dysfunction
- Patients with complete heart block or at risk for developing CHB (i.e. infra-nodal block):
- Mobitz I (if infra-nodal)
- Mobitz II
- 2:1 AV block (if infra-nodal)
- High grade AV block
- ECG with alternating LBBB and RBBB
- Syncope + BBB + HV interval > 70ms (HV interval is a measurement of His-Purkinje system to evaluate for conduction disease)
Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: Executive Summary, Journal of the American College of Cardiology (2018), doi: https://doi.org/10.1016/ j.jacc.2018.10.043.
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