DEAR DR. ROACH: At age 76, I was diagnosed with sinus node dysfunction last year after several episodes of what I’d call being “spaced out” (for lack of a better term). I couldn’t explain these instances to myself, much less anyone else lest they think I was crazy, until I had one where I passed out. This scared me, and I told my husband, who immediately made a doctor’s appointment.

The wise physician assistant sent me to a cardiologist who had me wear a heart monitor for two weeks. During this time, I had another episode that lasted for seven seconds, according to the very alarmed cardiologist. I was immediately scheduled for pacemaker surgery.

Could you please discuss sinus node dysfunction and enlighten me as to what caused it?

— G.W.T.

ANSWER: The sinus of the heart has nothing to do with your nose as you might guess; it’s a structure in the right atrium where blood flows into the heart from the venae cavae. It contains a structure called the “sinus node” or “sinoatrial node” that serves as the natural pacemaker for the heart.

If the SA node makes an electrical impulse, but it is poorly conducted, this results in SA block. The sinus node may be too slow (sinus bradycardia), or it may fail to make an impulse for a period of time, or even permanently (sinus pauses and sinus arrest). All of these are included in the umbrella term “sinus node dysfunction” (which used to be called “sick sinus syndrome” since it’s accompanied by periods of a too-fast heart rate).

When the sinus node fails to provide an impulse, other pacemakers in the heart will usually provide an “escape” beat, which prevents the symptom of being “spaced out.” Some people describe this as fatigue or lightheadedness. If there is no escape beat, then you will get a sinus pause as you did. When the sinus pause is very long, the person will often faint (which we term “syncope”).

The placement of a permanent pacemaker is the definitive treatment for sinus node dysfunction, but not everyone needs this. It’s also important to look for exacerbating factors (especially medicines but also thyroid disease, blockages of the heart arteries, liver disease, and low oxygen, among others) that can affect the sinus node.

These can make the disease of the sinus node become symptomatic due to fibrosis of the area around the SA node and its accompanying conduction tissue. Most of the time, no specific cause for sinus node dysfunction can be found, but systemic diseases like amyloidosis, sarcoidosis and hemochromatosis are rare causes of sinus node dysfunction.

ToYourGoodHealth@med.cornell.edu.