Before and After Lidocaine

This is an electrocardiographic (ECG) recording from a dog I saw this evening.

The left side of the image shows what is termed a highly regular broad-complex tachycardia (the heart rate is around 300 beats per minute). The right side shows an ECG from the same dog after treatment with lidocaine, an anti-arrhythmic drug (which is also a local anaesthetic and used to be called lignocaine). In the later tracing the heart rate is around 100 beats per minute and slightly variable - the variability is known as sinus arrhythmia and is evidence of healthy interaction between the heart and the brain.

Without treatment rapid heart rate can be rapidly fatal. The dog in question undoubtedly is still very unwell but we have now got the chance to find out exactly what's wrong with him and then to treat it.