Bradycardia pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: M.Umer Tariq [2] Ibtisam Ashraf, M.B.B.S.[3]

Overview

Bradycardia generally results from sinus node dysfunction and AV node dysfunction. However, other pathophysiologic conditions can also result in bradycardia such as acute Myocardial infarction, obstructive sleep apnea, exaggerated vagal activity, increased intracranial pressure, and infectious diseases such as Lyme disease, rocky mountain spotted fever, chagas disease, psittacosis, Q fever, and typhoid fever.

Pathophysiology

The underlying mechanism is not clinically relevant to the treatment.

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]^[2]

Disorders of the atrioventricular node (AV node)

Atrioventricular conduction disturbances 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:^[3]^[4]

Acute Myocardial infarction

Patients with acute myocardial infarction, especially those with the right coronary artery, are affected by bradycardia as it supplies the SA node.^[5]

Obstructive sleep apnea

Those with obstructive sleep apnea also have sinus bradycardia, which can be extreme (< 30 beats per minute) during apnea.^[6]

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.

Increased intracranial pressure

Increased intracranial pressure should be excluded when sinus bradycardia arises in a patient with neurological dysfunction. Sinus bradycardia is often associated with damage to the cervical or thoracic spine, where the sympathetic denervation of the heart leaves an uncontested parasympathetic tone.^[7]

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. ^[8]^[9]

Microscopic Pathology

On microscopic histopathological analysis, a few patients with sinus bradycardia may show no nodal histopathology, yet some microscopic findings are associated with the condition which includes the following:^[10]^[11]
- Nodal cell reduction
- Nodal cell and fibrosis
- Amyloidosis in the nodal region
- Sinus node hypoplasia

References

↑ Alpert MA, Flaker GC (1983). “Arrhythmias associated with sinus node dysfunction. Pathogenesis, recognition, and management”. JAMA. 250 (16): 2160–6. PMID 6620520.
↑ Brodsky, Michael; Wu, Delon; Denes, Pablo; Kanakis, Charles; Rosen, Kenneth M. (1977). “Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease”. The American Journal of Cardiology. 39 (3): 390–395. doi:10.1016/S0002-9149(77)80094-5. ISSN 0002-9149.
↑ “StatPearls”. 2020. PMID 29630253.
↑ Nof, Eyal; Luria, David; Brass, Dovrat; Marek, Dina; Lahat, Hadas; Reznik-Wolf, Haya; Pras, Elon; Dascal, Nathan; Eldar, Michael; Glikson, Michael (2007). “Point Mutation in the HCN4 Cardiac Ion Channel Pore Affecting Synthesis, Trafficking, and Functional Expression Is Associated With Familial Asymptomatic Sinus Bradycardia”. Circulation. 116 (5): 463–470. doi:10.1161/CIRCULATIONAHA.107.706887. ISSN 0009-7322.
↑ Davis WT, Montrief T, Koyfman A, Long B (August 2019). “Dysrhythmias and heart failure complicating acute myocardial infarction: An emergency medicine review”. Am J Emerg Med. 37 (8): 1554–1561. doi:10.1016/j.ajem.2019.04.047. PMID 31060863.
↑ 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.
↑ Gilson GJ, Miller AC, Clevenger FW, Curet LB (1995). “Acute spinal cord injury and neurogenic shock in pregnancy”. Obstet Gynecol Surv. 50 (7): 556–60. doi:10.1097/00006254-199507000-00022. PMID 7566833.
↑ 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.
↑ Nof E, Luria D, Brass D, Marek D, Lahat H, Reznik-Wolf H; et al. (2007). “Point mutation in the HCN4 cardiac ion channel pore affecting synthesis, trafficking, and functional expression is associated with familial asymptomatic sinus bradycardia”. Circulation. 116 (5): 463–70. doi:10.1161/CIRCULATIONAHA.107.706887. PMID 17646576.
↑ Sanders P, Kistler PM, Morton JB, Spence SJ, Kalman JM (2004). “Remodeling of sinus node function in patients with congestive heart failure: reduction in sinus node reserve”. Circulation. 110 (8): 897–903. doi:10.1161/01.CIR.0000139336.69955.AB. PMID 15302799.

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[pmid6620520-1] Alpert MA, Flaker GC (1983). “Arrhythmias associated with sinus node dysfunction. Pathogenesis, recognition, and management”. JAMA. 250 (16): 2160–6. PMID 6620520.

[BrodskyWu1977-2] Brodsky, Michael; Wu, Delon; Denes, Pablo; Kanakis, Charles; Rosen, Kenneth M. (1977). “Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease”. The American Journal of Cardiology. 39 (3): 390–395. doi:10.1016/S0002-9149(77)80094-5. ISSN 0002-9149.

[pmid29630253-3] “StatPearls”. 2020. PMID 29630253.

[NofLuria2007-4] Nof, Eyal; Luria, David; Brass, Dovrat; Marek, Dina; Lahat, Hadas; Reznik-Wolf, Haya; Pras, Elon; Dascal, Nathan; Eldar, Michael; Glikson, Michael (2007). “Point Mutation in the HCN4 Cardiac Ion Channel Pore Affecting Synthesis, Trafficking, and Functional Expression Is Associated With Familial Asymptomatic Sinus Bradycardia”. Circulation. 116 (5): 463–470. doi:10.1161/CIRCULATIONAHA.107.706887. ISSN 0009-7322.

[pmid31060863-5] Davis WT, Montrief T, Koyfman A, Long B (August 2019). “Dysrhythmias and heart failure complicating acute myocardial infarction: An emergency medicine review”. Am J Emerg Med. 37 (8): 1554–1561. doi:10.1016/j.ajem.2019.04.047. PMID 31060863.

[pmid17557424-6] 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.

[pmid7566833-7] Gilson GJ, Miller AC, Clevenger FW, Curet LB (1995). “Acute spinal cord injury and neurogenic shock in pregnancy”. Obstet Gynecol Surv. 50 (7): 556–60. doi:10.1097/00006254-199507000-00022. PMID 7566833.

[pmid11284920-8] 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.

[pmid15949188-9] 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.

[pmid17646576-10] Nof E, Luria D, Brass D, Marek D, Lahat H, Reznik-Wolf H; et al. (2007). “Point mutation in the HCN4 cardiac ion channel pore affecting synthesis, trafficking, and functional expression is associated with familial asymptomatic sinus bradycardia”. Circulation. 116 (5): 463–70. doi:10.1161/CIRCULATIONAHA.107.706887. PMID 17646576.

[pmid15302799-11] Sanders P, Kistler PM, Morton JB, Spence SJ, Kalman JM (2004). “Remodeling of sinus node function in patients with congestive heart failure: reduction in sinus node reserve”. Circulation. 110 (8): 897–903. doi:10.1161/01.CIR.0000139336.69955.AB. PMID 15302799.

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