Singapore - Cherish your memories

As each year passes, in our moments of reflection and contemplation, we often delve into our treasure trove of memories to indulge in the cherished moments and the wonderful experiences that have enriched our lives. These beautiful memories are the treasures that we yearn to preserve as we age.

The repository for memory in the brain is segregated into separate short-term and long-term memory areas. As we absorb what we sense around us, the outer layer of the brain, the cortex, is stimulated by our senses with different parts or lobes of the brain being activated by different sensations. The ability to store and recall these senses constitutes our memory.

While the transmission of these sensory data in the cortex may eventually result in some of it being stored in the frontal lobe (front part of brain) as short-term memory, the main centre for long-term data is in another part of the brain called the hippocampus. New memories converge on the hippocampus and circulate to the brain area adjacent to it, the limbic system, which controls emotions and spatial memory, and thereafter to the cortex where these memories circulate through the cortex and back to the hippocampus, creating and strengthening memory pathways.

Disruption of these pathways by strokes or degeneration will disrupt the pathways which are necessary for the retention of memory.

Silent strokes

While it has often been assumed that the relentless deterioration of memory is part and parcel of aging, a February 2012 study published in Neurology had shown that deterioration of memory can also be attributable to silent strokes. Silent strokes refer to minute areas of brain injury in less important areas of the brain which do not result in an obvious physical disability. Researchers estimate that more than one third of those over the age of 70 years have a silent stroke and this is associated with a two-fold risk of dementia and a more rapid decline in cognitive function. Hence, preventing silent strokes may allow us to preserve our memories.

Heart procedures

Silent strokes can occur when undergoing an invasive test, coronary angiogram (CA), to examine the heart arteries. This involves inserting tubes into the leg or wrist artery, injecting iodine containing dye into the heart artery and taking X-ray images. During the procedure, minute gas bubbles or microscopic particles (microemboli) generated may travel into the brain and cause strokes. Multiple prospective studies have demonstrated that CA carries a risk of silent stroke of 5-22 per cent. Currently, physicians and patients have more options with the availability of safer non-invasive alternatives such as computed tomography (CT) and magnetic resonance (MR) angiogram of the heart arteries.

Wrist or Leg?

Where a CA is required, the procedure can be performed via the wrist or leg artery. Over the years, there has been an increasing popularity with the wrist route, the reason being that ambulation can commence after the procedure instead of resting for six hours as for the leg route. A 2011 randomised study by researchers from Karolinska University Hospital, published in Stroke journal, comparing both routes demonstrated that CA performed via the wrist route generated significantly more particulate microemboli than the leg route. Another randomised study published in June 2012 in the Journal of the American College of Cardiology showed that CAs and angioplasties (procedures to open the heart arteries with balloons and/or stents) performed via the wrist route was also associated with a higher X-ray radiation dosage than the leg artery approach.

Hence, in deciding on the choice of the preferred route, whether the lower stroke risk and lower radiation risk of a leg approach should be sacrificed for the convenience of the wrist route is a decision that should not be taken lightly.

Heart surgery

Solving your heart problems can sometimes cause "headaches". There are those with significant blockage of the heart arteries who may have to undergo coronary artery bypass graft surgery (CABG). Multiple studies have shown that 30-65 per cent of patients undergoing CABG have evidence of cognitive impairment one month after CABG. A 2008 study by researchers led by Nathalie Stroobant, Ghent University Hospital, showed that 3-5 years after CABG, 30 per cent of the patients continued to show neurocognitive problems irrespective of the CABG technique used.

Abnormal heart rhythms

Beware of your heart palpitations. Among the abnormal heart rhythms, atrial fibrillation (AF), an irregular fast heart rhythm involving the left upper heart chamber is associated with blood clot formation and the clots can travel to the brain and cause strokes. In the 1995 SPINAF study published in Circulation journal, about 15 per cent of AF patients had silent strokes on CT scans. More recently, the ASSERT study published in the New England Journal of Medicine in January 2012 showed that in pacemaker patients, silent AF was seen in approximately one-third of patients and the presence of AF was associated with a 2.5-fold increase in the risk for stroke.

Sleep apnoea

Sleeping well may be important to preserving your memory. At the American Stroke Association's International Stroke Conference 2012, researchers from Dresden University found that sleep apnoea (decreased oxygen as a result of obstruction to breathing during sleep) was associated with stroke. Those who had more severe sleep apnoea were more likely to have silent strokes. More than 50 per cent of silent stroke patients had sleep apnoea. If you snore loudly and have a dry throat because you are breathing through your mouth, you may have sleep apnoea.

You can prevent silent strokes and preserve your memories by making the right choices:

1) Non-invasive tests instead of invasive CA;

2) For invasive procedures, choose the leg approach;

3) If you have abnormal heart beats, screen for AF;

4) If you suspect sleep apnoea, confirm it with a sleep apnoea test - clearing the nasal blockage with outpatient radio frequency ablation may suffice;

5) If you have high blood pressure, high cholesterol and diabetes mellitus, these risk factors for stroke will also need to be optimally managed.

Therefore, keeping those precious memories is a choice you can make.

Dr Michael Lim

The writer is medical director at the Singapore Heart, Stroke & Cancer Centre. He is also editor-in-chief, Heart Asia (a journal of the British Medical Journal Publishing Group); chairman, scientific advisory board, Asia Pacific Heart Association; and honorary professor and senior medical adviser, Peking University Heart Centre

This series is brought to you by the Heart, Stroke and Cancer Centre. It is produced on alternate Saturdays.

This article was first published in The Business Times.