Check-up: Sinus Node Dysfunction

I have a heart problem my doctor called sinus node dysfunction. What exactly is this?

Contraction of the muscle fibres in the heart is controlled by electricity that flows along distinct pathways, at a controlled speed. The electrical current that begins each heartbeat originates in the heart’s pacemaker, located in the top of the upper right chamber (right atrium). The rate at which the pacemaker discharges the electrical current determines the heart rate, which is regulated automatically by the autonomic nervous system.

Heart rate is also influenced by hormones released into the bloodstream such as adrenaline, noradrenaline and thyroid hormone.

Problems with the heart’s pacemaker may result in a persistently slow heartbeat (sinus bradycardia) or complete cessation of normal pacemaker activity (sinus arrest). Pacemaker dysfunction is more common among older people, in those with pre-existing cardiac conditions and diabetes. Some drugs and an underactive thyroid gland (hypothyroidism) can cause pacemaker dysfunction. The terms “sick sinus syndrome” or “sinus node dysfunction” are both used to describe this range of pacemaker problems.

Apart from feeling tired and fainting a couple of times, I had no other symptoms. What could have caused my condition?

Many types of pacemaker dysfunction cause no symptoms. A persistent slow heart rate commonly causes weakness and tiredness. Fainting may occur if the rate becomes very slow. A fast heart rate is often perceived by the person as palpitations. When the fast heart rate stops, fainting may occur if the pacemaker is slow in restarting normal heart rhythm. A slow pulse (especially an irregular one), a pulse that varies greatly without any change in the person’s activity, or a pulse that does not increase during exercise suggests pacemaker dysfunction.

A diagnosis of pacemaker dysfunction is usually based on presenting symptoms and the results of electrocardiography (ECG), particularly when heart rhythm is recorded over a 24-hour period with a Holter monitor.

I am going to need a pacemaker fitted. Is this the normal treatment for this condition?

People with symptoms are often given a permanent artificial pacemaker to accelerate the heart rate. Artificial pacemakers are electronic devices that act in place of the heart’s own pacemaker. Medication to slow the heart rate – beta blockers or calcium channel blockers – and other drugs may also be required for some, even after an artificial pacemaker has been fitted.