Bradycardia pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: M.Umer Tariq [2]
Overview
Pathophysiology
It is difficult and sometimes impossible to assign a mechanism to any particular bradycardia. However, the underlying mechanism is not clinically relevant to treatment, which is the same in both cases of sick sinus syndrome: a permanent pacemaker.
There are generally two types of problems that result in bradycardia:
Disorders of the sinus node
- Impaired automaticity - Sinus node dysfunction/sick sinus syndrome)[1]
- Exit block - Impaired conduction of the impulse from the sinus node into the surrounding atrial tissue
Disorders of the atrioventricular node (AV node)
- Atrioventricular conduction disturbances (1o AV block, 2o type I AV block, 2o type II AV block, 3o AV block) may result from impaired conduction in the AV node, or anywhere below it, such as in the bundle of HIS.
Sinus bradycardia can also be seen in these pathophysiologic settings:
Acute Myocardial infarcation
- Patients with acute myocardial infarction, especially those with the right coronary artery, as it supplies the SA node are affected by bradycardia.
Obstructive sleep apnea
- Those with obstructive sleep apnea also have sinus bradycardia, which can be extreme (< 30 beats per minute) during apnea.[2]
Exaggerated vagal activity
- Vasovagal responses may be associated with severe bradycardia due to elevated parasympathetic involvement and sympathetic suppression of the SA node. These stimuli include carotid sinus stimulation, vomiting, coughing, and Valsalva maneuver.
Infectious causes
- Infectious agents associated with relative sinus bradycardia include Lyme disease, Chagas disease, legionella, psittacosis, Q fever, typhoid fever, typhus, babesiosis, malaria, leptospirosis, yellow fever, dengue fever, viral hemorrhagic fevers, trichinosis, and Rocky Mountain Spotted fever. [3][4]
References
- ↑ Alpert MA, Flaker GC (1983). "Arrhythmias associated with sinus node dysfunction. Pathogenesis, recognition, and management". JAMA. 250 (16): 2160–6. PMID 6620520.
- ↑ Caples SM, Rosen CL, Shen WK, Gami AS, Cotts W, Adams M; et al. (2007). "The scoring of cardiac events during sleep". J Clin Sleep Med. 3 (2): 147–54. PMID 17557424.
- ↑ Cunha BA (2000). "The diagnostic significance of relative bradycardia in infectious disease". Clin Microbiol Infect. 6 (12): 633–4. doi:10.1046/j.1469-0691.2000.0194f.x. PMID 11284920.
- ↑ Puljiz I, Beus A, Kuzman I, Seiwerth S (2005). "Electrocardiographic changes and myocarditis in trichinellosis: a retrospective study of 154 patients". Ann Trop Med Parasitol. 99 (4): 403–11. doi:10.1179/136485905X36307. PMID 15949188.