Discussion
Cannabis consumption is mostly associated with chronic sinus tachycardia
and other tachyarrhythmia like atrial fibrillation and ventricular
tachycardia. A scoping study of 27 cases of arrhythmia associated with
marijuana reported that most cases were young males and the mortality
rate was high with Marijuana associated arrhythmia (11%). Atrial
fibrillation (26%) and ventricular fibrillation (22%) were the most
common arrhythmias. Brady arrhythmia were not common; first and second
degree AV block and sinus arrest (3.7 % each) were the common findings
among bradyarrythmia group14 In another extensive
review about the association of cannabis use and cardiac dysrhythmias,
out of 42 subjects, third degree AV block was found in 12% of cases
while symptomatic bradycardia was present in 10 % of the cases .15
Table 1 depicts reported cases of severe bradyarrythmia due to marijuana
toxicity. Till date about eleven cases of severe bradyarrythmia are
reported, out of which three cases were third degree heart block, two
cases were second degree heart block and six cases were of sinus arrest.
Pacemaker implantation was done in two cases of complete heart block and
3 cases of sinus arrest and in rest of the five cases conduction
improved after abstinence from marijuana while one case was lost to
follow-up. In none of the reported cases electrophysiological study was
done to determine the site of blockade.
There are several proposed mechanisms for tachyarrhythmias caused due to
cannabis like altered conduction property of myocardial tissue; cardiac
ion channel modulation; autonomic dysfunction due to imbalance between
sympathetic and parasympathetic outflow; type 2 myocardial infarction
due to tachycardia, elevated carboxyhaemoglobin , slow coronary flow due
to endothelial dysfunction, coronary vasospasm, increased platelet
aggregation leading to ischaemic injuries/ scar creating a milieu for
arrhythmia. However the exact mechanism by which it causes
bradyarrythmia is not well known .1,2 Agonistic action
of THC on CB1R causes sympathetic inhibition and increased cardiac vagal
tone leading to bradycardia, lower doses cause sympathetic stimulation
while higher doses is associated with parasympathetic action. The
electrophysiological effects of intravenous THC in human experimental
studies on cardiac conduction includes a change in P wave morphology,
decrease in sinoatrial (SA) conduction, delay in A-H (atrium to his
bundle) interval and decrease in atrioventricular (A-V) node refractory
period. However, In this case the HV interval was mildly prolonged ,
which is not explainable completely by previously described mechanisms
and it is possible that Δ9-tetrahydrocannabinol (THC) has some direct
toxic effects on cardiac conduction systems through cannabinoid
receptors 1. Figure 3 demonstrates the possible mechanism of bradycardia
caused by cannabis. Our Patient, who was young medical professional
consumed marijuana for about 4 years and his previous medical record
were not suggestive of any risk factor for complete heart block except
chronic marijuana use. After initial evaluation he was implanted
permanent pacemaker. During follow-up patient claimed complete
abstinence from marijuana use. Patient atrio-ventricular conduction also
improved in about 3 months duration.
Marijuana use is increasing world over for both medicinal and
recreational purposes as states are legalizing cannabis and physicians
can expect to encounter more patients who use or abuse marijuana .It can
cause severe bradyarrythmia, possibly mediated by enhanced vagal tone
and might be reversible in case of withdrawal of usage. Awareness
regarding such cardiovascular side effects of marijuana is warranted.
Screening for marijuana use should be encouraged, especially in young
patients presenting with cardiovascular disease.
Contributorship : All authors were equally involved in patient
care , drafting and editing of the manuscript