Q My friend’s ECG shows a ‘prolonged QT interval’. Why is this dangerous?

A ECGs (heart tracings) provide information about electrical activity and the shape/size of heart muscles and valves during each heartbeat. The size, pattern and distances (intervals/ time) between the electrical waves (P,Q,R,S,T and U) can be used to diagnose heart damage such as heart attacks, irregularities such as atrial fibrillation, heart strain and leaky/narrowed valves. A prolonged QT interval means the heart is taking longer to recharge between beats; it affects around one person in 2,000, although many aren’t aware they have it.

It can be inherited (a genetic defect affecting chemicals inside heart muscle cells) and cause heart rhythm problems with palpitations, dizziness, blackouts or even cardiac arrest; these may occur in childhood or later life, or be triggered by sudden stress, noise, exercise or during sleep. Your friend may need treatment with drugs or even a pacemaker; near-relatives may be at risk and need testing too

(see bhf.org.uk).

Prolonged QT syndrome can also be triggered by medicines, such as antibiotics, antidepressants, antihistamines, ‘water pills’ and some that are used to treat heart disease or psychosis, so your friend will be given a list of pharmacy and prescription drugs to avoid.