Understanding ECGs: tachycardias
In the third article in our series Dominic Cox and Hamish Dougall discuss the main types of tachycardia
Tachycardias are the most exciting part of learning about ECGs. It is of course important to understand the mechanism causing tachycardias, but it is equally important to remember to look at the patient first. “Benign” arrhythmias can compromise a person, and “serious” arrhythmias can be asymptomatic. Look at the patient and act with commonsense, rather than treating the ECG.
We are not going to try to explain the emergency treatment of arrhythmias, but this should be something on all doctors' minds (and hearts). All the emergency treatment protocols are available from the European Resuscitation Council (website www.erc.edu/).
Tachyarrhythmias can be divided into two broad categories: supraventricular tachycardias (SVT) and ventricular tachycardias (VT). It is useful to think of these as narrow complex (QRS complex <120ms) tachycardias (SVT) and broad complex (QRS >120 ms) tachycardias (VT).
As described in the previous articles,12 normally the atrium passes the sinoatrial (SA) node's signal