Effect of poisons on heart rhythm

Cardiotoxic substances, i.e. substances poisonous to  the heart  , are all substances that interfere with its proper function.

The cardiovascular system is the site of specific action of some alkaloids  and so-called cardiac glycosides such as digitalis (see  Effect of drugs on heart rhythm  ) or andromedotoxin, which is contained, for example, in azaleas and rhododendrons, and from them, with the nectar collected by bees, reaches their honey, which becomes poisonous. Many peptide toxins  of snakes also have a cardiotoxic effect, e.g. cardiotoxin from cobra venom, cardiotoxins from sea anemones, toxic peptides from hummingbirds and the like. All substances that disrupt the heart rhythm or interfere in some way with the electrical activity of the heart act as cardiotoxins.

also have a cardiotoxic effect A number of drugs, such as the chemotherapeutic agent 5-fluorouracil (a pyrimidine analogue), anthracycline  antibiotics  , fenfluramine, etc. Other "heart poisons" include, for example, mercury or cocaine.

Andromedotoxin (Grayanotoxin)
It is a toxin (polyhydroxylated cyclic diterpene) found in rhododendrons and other plants in the Ericaceae  family. It binds to the sodium channels of cell membranes and prevents the inactivation of excitable cells, leaving them depolarized. Initial symptoms of poisoning are hypotension  and  sinus bradycardia. In higher concentrations, it also causes bradycardia, ventricular tachycardia and Wolff-Parkinson-White syndrome. can be used for therapy  Atropine  or vasopressors.

Anthracycline
Anthracycline cardiotoxicity is characteristic of this chemotherapeutic agent. It can be caused by several factors - interference with the ryanodine receptors of the sarcoplasmic reticulum of cardiomyocytes, the formation of free radicals or the formation of metabolic products of anthracycline in the heart. Cardiotoxicity is manifested by changes on the ECG  and  arrhythmias  or  cardiomyopathy  leading to congestive  heart failure. Dexrazoxane is sometimes used to reduce cardiotoxic effects.

Mercury
Mercury intoxication is cumulative, acute poisoning occurs when mercury vapor is inhaled. Since mercury blocks the degradation process of catecholamines  (inactivates S-adenosylmethionine and thus prevents the catabolism of catecholamines by catechol-o-methyltransferase), an excess of  adrenaline  causes, among other things, tachycardia and  hypertension.

Cocaine
It is an alkaloid of the South American coca  bush. In addition to other effects, it increases blood pressure and heart rate (stimulant of the central nervous system). It temporarily increases the production of dopamine  and  serotonin. Cocaine overdose causes high blood pressure and abnormalities in heart  function (contractions are either extremely fast or slow; too strong or weak). This can lead to death, especially in people who already have heart disease.

5-fluorouracil
The incidence of cardiotoxicity associated with 5-fluorouracil (5-FU) is dependent on its dose and timing. The mechanism of cardiotoxic action is not known, although several hypotheses have already appeared, for example coronary artery  spasm caused directly by the drug or an allergic reaction or a direct toxic effect on  the myocardium  and  pericardium. Adenosine analogs have several hemodynamic effects including changes in left ventricular contractility or peripheral vasodilation or vasoconstriction. The most common symptoms of poisoning include chest pain, unstable angina , ST-T wave changes, and  atrial fibrillation. Rarely, ventricular fibrillation or sudden death can occur.

Reference

 * 1) Wikipedia (User: 212). Grayanotoxin [online]. ©2004. Poslední revize 2007, [cit. 22. 9. 2009]. < https://en.wikipedia.org >.
 * 2) TALAPATRA, K., I. RAJESH a B. RAJESH, et al. Transient asymptomatic bradycardia in patients on infusional 5-fluorouracil (J Can Res Ther 2007;3:169-71) [online]. ©2007. [cit. 22. 9. 2009]. .
 * 3) NOVOTNÝ, Jan. Kardiotoxicita 5-fluorouracilu [online]. ©2002. [cit. 22. 9. 2009]. .