This question is often asked by heart patients on blood-thinning drugs, and it is a difficult one to answer. By Michael Lim

IT is not uncommon for heart patients on blood-thinning drugs to ask whether they can stop taking them because of upcoming dental or other surgery.

The answer: It depends.

Heart patients at risk of complications upon stopping blood thinners include those with stents in their heart arteries, those with artificial heart valves, artificial heart pumps and those with an irregular heart rhythm, atrial fibrillation, which is associated with an increased risk of stroke.

Metallic stents

Most patients with stents – the cylindrical metal meshes placed in their heart arteries to keep them clear of blockages – consume two blood thinning drugs. These are most commonly aspirin and clopidogrel, consumed for at least a year, after which one is discontinued.

The hardest question to answer is: when can such drugs be stopped safely?

With a long holiday weekend approaching, I had been looking forward to a good rest when I was called to the Emergency department at night to attend to Mr A, who had chest pain.

He had had drug-eluting stents (DES), which are stents coated with a drug-containing polymer, in three of his major heart arteries four years ago.

Caught up with the preparations for the festive season, he went without medication for two weeks after running out of it. On that fateful day, after a hectic day of springcleaning, he had felt weak, light-headed and had some uneasiness over his chest. Alarmed, he went to the emergency department.

His electrocardiogram or ECG, an electrical recording of the heart, showed signs consistent with a major heart attack. The team was mobilised and within half an hour, swung into action just past midnight.

The gravity of the situation was apparent only when the coronary angiogram (X-rays of the heart arteries) showed that all his three major heart arteries were blocked with blood clots. After an hour, the clots were removed and the occluded segments of the arteries, successfully opened. He went home a few days later, with most of his heart function preserved.

In the Swedish Coronary Angiography and Angioplasty Registry of more than 94,000 stent implantations, the incidence of clot formation in bare metal stents – those with no polymer coating – at one year was about 1.1 per cent; it was uncommon after one year.

For DES, the cumulative incidence at one year was approximately 0.4 to 0.8 per cent. The new-generation DES fares even better at the two-year mark, with a clot formation incidence of 0.6 per cent. (It is 2.4 per cent for the first-generation DES.)

While the likelihood of sudden clot formation is generally extremely low after five years of stent implantation, one cannot be absolutely certain this will never happen, but the likelihood appears to be very low with the newer generation of DES.

Heart valves and pumps

For those whose damaged heart valves have been replaced with mechanical valves, taking warfarin, a Vitamin K antagonist blood-thinning agent, is necessary. Similarly, for those with weak hearts supported by implanted artificial heart pumps, blood-thinning medication is also necessary. Stopping this medication may result in clot formation and malfunction, with dire consequences.

Abnormal heart rhythms

Among those with abnormal heart rhythms, atrial fibrillation is the one that is associated with an increased risk of stroke. Blood-thinning is generally advocated.

However, unlike stents and mechanical heart implants, the risk of a sudden complication upon cessation of blood thinners is relatively lower.

Silver lining

Patients with mechanical heart valves and heart pumps constitute a small proportion of the patients on blood-thinning agents. The largest proportion of heart patients on such drugs are those with blockage of the heart arteries and within this category, those with stents have the highest risk of complications upon cessation of blood-thinning medication.

Fortunately, the day has arrived when blood-thinning agents can be permanently discontinued for those with implanted stents. The latest generation of “non-metallic stent” is made of bio-absorbable polymer material which becomes incorporated into the vessel wall within months; by the three-year mark, most of the polymer stent would have dissolved, leaving behind a pristine vessel lumen.

However, there is a small risk of clot formation in the stent soon after implantation if the stent is not optimally implanted; this can happen even in the best of hands.

Given the possibility of having no metal in the heart arteries and no need for permanent blood-thinning agents, it is therefore not surprising that more and more patients who are suitable for this are opting for this polymer stent which can dissolve. Its only downside: its high cost.

Fortunately, the day has arrived when blood-thinning agents can be permanently discontinued for those with implanted stents. The latest generation of ‘non-metallic stent’ (above) is made of bio-absorbable polymer material which becomes incorporated into the vessel wall within months.