Many toxic substances cause SVTs, usually sinus tachycardia.
In addition, supraventricular tachycardias may be observed in many intoxications as a secondary response to hypoxaemia, hyperthermia, methaemoglobinemia, hypovolaemia or peripheral vasodilation. Conscious patients may be aware of palpitations. If the rate is very fast, and the patient has pre-existing cardiovascular compromise or is hypovolaemic, impaired cardiac filling may lead to hypotension and hypoperfusion. In such cases, the patient may experience dizziness, weakness, altered mental status, anxiety, chest pain or syncope. In most cases, the only treatment is initial cardiac monitoring, establishment of intravenous access, supplemental oxygen and simple observation.