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A 27-year-old man is admitted to the hospital after repeated fainting episodes. On admission, he tells you that he has been passing out at least twice a month for the last 5 years.

He is employed as a carpenter, and notes that his syncope caused a traffic accident in the past that injured his cervical spine.

He notes that his family history does not include syncope, ischemic heart disease, sudden death, or any acquired cardiac conditions. Although he admits to smoking marijuana daily, he does not drink alcohol or smoke tobacco.

Physical examination finds him healthy and relaxed in appearance. He has a resting heart rate of 54 beats per minute, blood pressure 126/74 mm Hg, and respiratory rate of 16 breaths per minute. Orthostatic assessment results are normal.

A cardiovascular examination notes normal heart sounds with no gallops, rubs, or murmurs, and no cardiovascular system (CVS) abnormalities. Clinicians find no evidence of cyanosis, clubbing, or peripheral edema, and on auscultation, his chest is clear.

Laboratory tests

Assessments return normal results for complete blood count, cardiac troponins, thyroid stimulating hormone, and electrolytes. Resting electrocardiogram (ECG) showed sinus bradycardia with ventricular rate of 43 beats/minute with no evidence of atrioventricular block, sinus pause, or ischemic changes. Notably, no syncopal episodes are observed. The urine drug screen confirms the patient's reported marijuana use.

Clinicians perform a transthoracic echocardiogram at the time of the patient's hospitalization: findings reveal a normal ejection fraction, and no structural, valvular, and/or wall motion abnormalities are detected.

Myocardial perfusion stress test and tilt table test results are also unremarkable.

Given the absence of any evidence of cardiac dysfunction, despite his reported long-term history of recurrent syncope, a loop recorder is implanted to evaluate the cause of syncope. The patient is discharged from the hospital.

Within 1 week of discharge, the man returns due to another episode of syncope. Findings are positive for a long sinus pause of more than 3 seconds duration, indicative of sick sinus syndrome (Figure).

Treatment and Outcome

The patient is re-hospitalized and provided with a cardiac monitor, which detects periodic runs of atrial fibrillation. Based on the patient's recent and long-term history, clinicians diagnose sick sinus syndrome. In consideration of his occupation and his previous car accident, he undergoes implantation of a dual chamber permanent pacemaker.

Case Follow-up

Following his discharge, the patient receives a dual chamber permanent pacemaker. For 6 months thereafter, he is followed without evidence of any new symptoms or recurrence of syncope. Based on the lack of evidence for any other cause of his symptoms, clinicians strongly suspect that marijuana is the cause of this patient's sick sinus syndrome.

Discussion

Authors of this ¹ describing a previously unreported probable link between chronic marijuana use and sick sinus syndrome note that their report adds to previously documented cases of marijuana-induced asystole, vasovagal syncope, and cardiac arrest.^2,3

Alluding to the wide-spread legalization of marijuana⁴ and its for both recreational and therapeutic reasons,⁵ case authors note the need for further investigation into the cardiac effects of smoking marijuana, such as sick sinus syndrome.

Marijuana use can have a range of cardiac effects, including bradycardia, sinus pauses, tachycardia, and orthostatic hypotension.⁶ The underlying mechanism of this is either sympathetic or parasympathetic drive,⁷ case authors explain. Marijuana decreases the amplitude of P-wave, significantly decreases the mean sinoatrial time, and mean atrioventricular conduction time, with the potential to cause atrial and ventricular arrhythmias.

Sick sinus syndrome describes the inability of the heart to perform its pacemaking function. The condition encompasses various arrhythmias like bradyarrhythmias with or without associated tachyarrhythmias. The condition has intrinsic etiologies -- such as sinoatrial nodal remodeling, ion channel dysfunction, and sinoatrial nodal fibrosis.^8-10 External contributors include metabolic disturbances, autonomic dysfunction, and medications including calcium channel blockers, antiarrhythmics, beta blockers, sympatholytic medications, digoxin, and lithium.^10,11

In its early stages, sick sinus syndrome often has no symptoms, and ECG findings may also be normal, case authors point out.^12-14

Advanced disease tends to present with end-organ hypoperfusion symptoms such as cerebral hypoperfusion, which results in syncope.¹⁵ Diagnostic signs on ECG is more likely to show bradyarrhythmias like sinoatrial pauses, sinoatrial exit block, sinus bradycardia, or sinus arrest.

Symptoms of Sick Sinus Syndrome:¹⁶

• Fatigue
• Transient lightheadedness
• Palpitations
• Angina
• Confusion
• Congestive heart failure
• Transient ischemic attacks
• Stroke
• Gastrointestinal symptoms
• Oliguria

Recommended treatment for is permanent implantation of a pacemaker -- which represents the only effective intervention for chronic sick sinus syndrome not due to extrinsic factors.¹⁷

Authors write that smoking marijuana regularly has many adverse cardiovascular effects. While these may not be serious in most young and healthy users, risk increases among users with cardiac diseases due to increased catecholamine levels and cardiac work.¹⁸ They conclude that this case adds to the literature showing that several reversible etiologies are associated with the development of sick sinus syndrome, in which marijuana abuse can be one of them.

References

1. Iqbal AM, et al: Marijuana Induced Sick Sinus Syndrome: A Case Report. Am J Case Rep 2019; 20: 882-885

2. Akins D, Awdeh MR: Marijuana and second-degree AV block. South Med J, 1981; 74(3): 371–73

3. Dockery BK, Newman KP: Exercise-induced asystole with syncope in a healthy young man. Am J Med Sci, 2007; 334(2): 145–48

4. Hasin DS: US epidemiology of cannabis use and associated problems. Neuropsychopharmacology, 2018; 43(1): 195–212

5. Rezkalla S, Kloner RA: Cardiovascular effects of marijuana. Trends Cardiovasc Med, 2018 [Epub ahead of print]

6. Semelka M, et al: Sick sinus syndrome: A review. Am Fam Physician, 2013; 87(10): 691–96

7. Huestis MA: Pharmacokinetics and metabolism of the plant cannabinoids, delta9-tetrahydrocannabinol, cannabidiol and cannabinol. Handb Exp Pharmacol, 2005; (168): 657–90

8. Dobrzynski H, et al: New insights into pacemaker activity: Promoting understanding of sick sinus syndrome. Circulation, 2007; 115(14): 1921–32

9. Adán V, Crown LA: Diagnosis and treatment of sick sinus syndrome. Am Fam Physician, 2003; 67(8): 1725–32

10. Mangrum JM, DiMarco JP: The evaluation and management of bradycardia. N Engl J Med, 2000; 342(10): 703–9

11. Oudit GY, et al: Lithium-induced sinus node disease at therapeutic concentrations: Linking lithium-induced blockade of sodium channels to impaired pacemaker activity. Can J Cardiol, 2007; 23(3): 229–32

12. Epstein AE, et al: ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons [published corrections appear in J Am Coll Cardiol, 2009; 53(16): 1473, and J Am Coll Cardiol, 2009; 53(1): 147]. J Am Coll Cardiol, 2008; 51(21): e1–e62

13. Keller KB, Lemberg L: The sick sinus syndrome. Am J Crit Care, 2006; 15(2):226–29

14. Lamas GA, et al: Mode selection trial in sinus node dysfunction. Ventricular pacing or dual-chamber pacing for sinus node dysfunction. N Engl J Med, 2002; 346(24): 1854–62

15. Zipes DP, et al: Guidelines for clinical intracardiac electrophysiological and catheter ablation procedures. A report of the American College of Cardiology/American Heart Association Task Force on practice guidelines. (Committee on Clinical Intracardiac Electrophysiologic and Catheter Ablation Procedures). Developed in collaboration with the North American Society of Pacing and Electrophysiology. J Am Coll Cardiol, 1995; 26(2): 555–73

16. Rodriguez RD, Schocken DD: Update on sick sinus syndrome, a cardiac disorder of aging. Geriatrics, 1990; 45(1): 26–30, 33–36

17. Dakkak W, Doukky R: Sick Sinus Syndrome. [Updated 2019 Jun 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan Available from: https://www.ncbi.nlm.nih.gov/books/NBK470599/

18. Jones RT: Cardiovascular system effects of marijuana. J Clin Pharmacol, 2002; 42(S1): 58S–63S

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