From the Guidelines
THC is not generally considered a QT-prolonging drug, and current evidence does not suggest it directly causes significant QT interval prolongation. When considering the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death, as outlined in the 2017 AHA/ACC/HRS guideline 1, the focus is on avoiding QT-prolonging medications in patients with long QT syndrome unless no alternative is available. While this guideline highlights the importance of monitoring the QTc interval during therapy with QT-prolonging medications, it does not specifically mention THC as a QT-prolonging agent.
The primary concern with THC and cardiac function relates more to its effects on the autonomic nervous system and cannabinoid receptors in the heart and blood vessels, which can lead to mild tachycardia and changes in blood pressure. However, these effects do not typically result in significant QT interval prolongation. For patients with pre-existing heart conditions or those taking medications known to prolong the QT interval, caution is advised due to potential indirect effects on cardiac function.
Key points to consider include:
- THC's impact on the autonomic nervous system and cannabinoid receptors
- Potential for mild tachycardia and changes in blood pressure
- Importance of discussing cannabis use with healthcare providers, especially for those with cardiac risk factors or taking other medications
- The need for careful monitoring in patients with long QT syndrome, as outlined in the guideline 1, although THC is not specifically identified as a risk factor.
From the Research
QT Prolonging Drugs
- The QT interval represents ventricular depolarisation and repolarisation, and prolongation of this interval can lead to life-threatening complications, including arrhythmias such as Torsades de Pointes and Ventricular Fibrillation 2.
- Many drug therapies are associated with prolongation of the QT interval, which may increase the risk of Torsades de Pointes (TdP), a potentially life-threatening cardiac arrhythmia 3.
- Non-cardiac drugs, such as antipsychotics, antidepressants, and macrolides, may prolong the QT interval, especially in case of overdosage or pharmacokinetic interactions 4.
Risk Factors for QT Prolongation
- Patient-related risk factors, such as female sex, age >65 years, and uncorrected electrolyte disturbances, can increase the risk of QT prolongation 3.
- Co-prescribed medicines that could increase the risk of QT prolongation, such as azole antifungals, macrolide antibacterials, and class-I or -III antiarrhythmic agents, should be considered 4.
- Other factors influencing QT interval, such as hypokalemia, hypomagnesemia, bradycardia, increased age, female sex, congestive heart failure, and polymorphisms of genes coding ion channels or enzymes involved in drug metabolism, should be taken into account 5.