Okay, here we go… the long awaited for (sarcasm) first post of my cardiac rhythm series. I figured we ought to start slow, so sinus bradycardia seemed to be fitting. Depending on your experience, you’re either closing out this page as you roll your eyes because “I’m not wasting my time reading that” or strapping in for the single greatest blog post about sinus brady ever typed.
Sinus bradycardia is when the heart pumps less than 60 beats per minute. The rhythm originates in the sinoatrial node a.k.a sinus node a.k.a SA node- whatever you want to call it, it’s the primary pacemaker of the heart which normally beats 60-100 times/minute. It looks like this on a tele strip:
Not everyone will experience symptoms, but symptoms will most commonly include hypotension, lightheadedness, altered level of consciousness, premature ventricular contractions, and syncope1.
Bradycardia can be caused by several things- some benign, some not. Some conditions- hypopituitarism, myxedema, obstructive jaundice- may cause SB due to their depressive effects on the SA node1. If someone has a damaged SA node, as seen with aging, ischemia, or sick sinus syndrome, it may still fire but at a decreased rate.
The SA node is supplied by the right coronary artery in 55% of individuals and the circumflex artery in the other 45%- knowledge bomb1.
Increased vagal tone is another culprit which can include gagging, vomiting, straining with stool, and tracheal suctioning1. If you see your patient starting to brady on the tele monitor, maybe they’re just straining super hard taking a BM. Crack open the door, stick your head in, and politely remind them to take the damn Colace next time as you take their vital signs while they’re on the toilet.
Many medications can cause bradycardia- beta-blockers, digitalis, and narcotics to name a few2. If your patient starts a beta blocker or has a dosage increase, keep an eye on their HR throughout the day to make sure they tolerate the change.
Like I said, sinus bradycardia isn’t always harmful. Many athletes may present with sinus bradycardia because they have an increased stroke volume (amount of blood ejected by the left ventricle with each contraction). If someone is bradycardic, they may be into endurance sports like distance running, swimming, or cycling. Hey, maybe they’re one of those cool cross-fitters you see on the IG.
Okay, one last thing for this section- it’s not uncommon to brady down while sleeping. Some may drop 10-20 bpm while they sleep from their typical heart rate. This is generally benign, but it can also result from obstructive sleep apnea, so be sure to assess each situation carefully1, 3.
Let’s wrap this up with how to treat sinus bradycardia. I’ll try to keep this short (no promises) because even if you’re still reading you probably have better things to do. If an individual is asymptomatic, they will typically receive no treatment1. For severe symptomatic bradycardia on an emergency basis, IV atropine will be administered.
Atropine is an anti-muscarinic drug which increases the rate the SA node fires and speeds conduction through the AV node4. It also opposes the vagal nerve activity- remember the straining? Dosing guidelines are 0.1 mg/kg which is usually between 0.5 and 1 mg (max dose 3 mg)2. For those of you who work/will be working with heart transplant patients, they are unaffected by atropine due to the denervation resulting from the transplant procedure1. These individuals will require isoproterenol (2-10 mcg/min)1.
As a last resort, pacemaker support is utilized to keep a patient’s rate elevated. If you don’t know much about pacemakers, look it up cause we ain’t got time for that on this post. What I will say is that atrial pacing is preferred to take advantage of the 20-30% increase in stroke volume that results from the contribution of atrial filling2. If the person has abnormal AV conduction as in 2nd or 3rd degree AV block, AV pacing should be used2. Ventricular pacing can be used, but it’s shown to be less effective than supraventricular mechanisms2.
- University of Maryland Medical Center Office of Clinical Practice and Professional Development. (2014). Introduction to cardiac rhythm interpretation (6th ed.).
- Bojar, R. M. (2016). Manual of perioperative care in adult cardiac surgery (5th ed.). West Sussex, UK: Wiley-Blackwell
- Gula, L. J., Krahn, A. D., Skanes, A. C., Yee, R., & Klein, G. J. (2004). Clinical relevance of arrhythmias during sleep: guidance for clinicians. Heart,90(3), 347–352.
- Swift, J. (2013). Assessment and treatment of patients with acute unstable bradycardia. (Cover story). Nursing Standard, 27(22), 48-56.
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