Thanks you, Arvind, for presenting a case of an older man with exercise-induced bradycardia found to have complete heart block 2/2 to cardiac sarcoidosis.
- In the consideration of bradycardia, one must first rule out MI. 15% of patients with an MI will present with complete heart block.
- Bradycardia in an inferior or posterior MI is driven by 1) ischemia AND 2) the Bezold-Jarisch Reflex. This is a cardiovascular decompressor reflex involving a marked increase in vagal (parasympathetic) efferent discharge to the heart, elicited by stimulation of chemoreceptors, primarily in the left ventricle.
- Complete AV dissociation with Ps faster than SLOW QRSs suggests complete heart block.
Etiology of Bradycardia
- Healthy children/adults during sleep (HRs in 30s, pauses up to 2 seconds may occur)
- Well-conditioned athletes
- Some elderly patients
An easy way to break down bradycardia is into extrinsic vs intrinsic causes.
- Idiopathic degenerative d/o
- Ischemia (ACS or chronic)
- Lyme disease
- Viral myocarditis
- Drugs – antiarrhythmics, b-blocker, calcium channel blocker
- Vagal tone
Evaluation of Patient with Complete Heart Block
- Rule out Ischemia – ~15% of patient with an acute MI will have complete heart block (usually RCA)
- Check for systemic, reversible causes of heart block:
- Meds: Digoxin, beta-blockers, calcium channel blockers, or anti-arrhythmics
- Electrolyte abnormalities – hypokalemia
3. Look for the primary cardiac causes in 3 broad categories:
- Infiltrative: Amyloidosis, hemochromatosis, sarcoidosis
- Inflammatory: SLE, scleroderma
- Infectious: Rheumatic fever, Chagas, endocarditis, viral myocarditis,i syphilis, Lyme disease
Diagnostic Criteria for Cardiac Sarcoid
Here is a great JACC review on cardiac Sarcoidosis – http://www.onlinejacc.org/content/68/4/411