Caffeine and its effects on the heart: The lowdown
Channel: York Cardiology
Date: 01/11/2019

There is a perception within the public and many healthcare professionals that ingestion of caffeine may contribute to the development of heart rhythm disturbances and this leads to an almost universal recommendation in patients with heart palpitations to abstain from caffeine. In this blog, I wanted to explore the evidence or lack of to support this proposition.
 
Caffeine is a stimulant and is found in different concentrations in a variety of commercially available beverages including soda (coca-cola), green tea, black tea, coffee and energy drinks. To give you an idea of content, a 375mls can of coca cola contains 32mg of caffeine, a cup of green tea about 35mg of caffeine, a cup of coffee 95mg of caffeine, an espresso shot 106 mg of caffeine and some energy drinks contain up to 500mg of caffeine per can. 
 
Caffeine has a half -life of 5.7 hours, and reaches maximum concentrations within 1 hour of consumption. It has nearly 100% bioavailability.
 
It has 4 main effects on the cardiovascular system. The first 2 can potentially increase its arrhythmic effects and the last 2 could possibly possibly represent antiarrhythmic effects. 
 
It causes sympathetic activation – 250 mg of caffeine will increase norepinephrine and epinephrine by 75% and 207%. At very high doses, caffeine may be pro-arrhythmic. This has been shown in rat models where giving them very high amounts of caffeine actually resulted them in developing sinus tachycardia, ectopic and ventricular fibrillation.
 
It can increase the amount of calcium within the cells. Caffeine does increase the sinus rate by both sympathetic activation and increasing the intracellular levels of calcium.
 
It has an inhibitory effect on adenosine receptors – Adenosine can reduce atrial refractoriness and trigger atrial fibrillation during acute administration.
 
It is an anti-oxidant and has a higher level of antioxidant activity properties than black tea.