Slow Heartbeat & Heart Block

The heart's own electrical wiring

Each heartbeat starts in a natural pacemaker called the sinus node, in the upper right chamber. The signal then passes through a relay point, the AV node, to the lower chambers, which do the pumping. If the sinus node fires too slowly or pauses (sick sinus syndrome), or if the signal is delayed or blocked on its way down (heart block), the heart rate drops. The brain and muscles may then get less blood than they need.

A slow pulse is not always a problem. Fit young people and athletes often have a resting rate in the 50s, and the rate normally falls during sleep. It matters when it causes symptoms or when the block is advanced.

Degrees of heart block

• First degree: signals are delayed but all get through. Usually only watched.
• Second degree: some beats are dropped. One type is usually mild; another type (Mobitz II) often needs a pacemaker.
• Third degree (complete): no signals get through, and the lower chambers beat on their own at a slow rate. This usually needs a pacemaker.

Possible causes

Age-related wear of the heart's wiring is common. Other causes include a heart attack, some medicines (such as beta-blockers, certain BP and rhythm medicines, and digoxin), an underactive thyroid, high potassium, some infections, and heart surgery. Your doctor checks for reversible causes first.

Tests that help

An ECG, a 24 to 48 hour Holter monitor to catch slow spells, an echocardiogram, thyroid and potassium blood tests, and sometimes a TMT to see whether the heart rate rises properly with exercise.

Treatment

If a medicine is the cause, your doctor may adjust or stop it. When symptoms continue or the block is advanced, a permanent pacemaker is the standard treatment. It is a small device placed under the skin below the collarbone, with a lead into the heart, that gives a beat whenever the heart's own rate is too slow.

When it is urgent

Fainting, a very slow pulse with chest pain or breathlessness, or sudden confusion need urgent care. Call 108 and see the emergency page.

Diagnosis and treatment are decided only after examination by your doctor. This page is for understanding the condition.