Do not take aspirin for prevention of heart attack if you do not have significant heart disease. There is no definitive evidence that aspirin is effective for those who have never had a heart attack. By Michael Lim

WITH an ageing population and with advances in medicine, more people are taking blood thinning drugs daily for the prevention and treatment of stroke and heart disease. A common question is whether taking an aspirin a day is useful. Before commencing on these drugs, it is important to understand whether blood thinning agents are safe and what the precautions are to prevent bleeding complications.

Types of blood thinning agents

Blood thinning agents can be broadly divided into two groups. The first, termed anti-platelet drugs, encompasses all the drugs that prevent clot formation by preventing blood platelets from clumping together. When platelets clump together, a biological reaction is activated and a clot is formed. This is frequently the mechanism for a heart attack. In a heart attack, the inner lining of the channel at the site of the narrowed segment of the artery may tear (“plaque rupture” ) and the body reacts by activating the platelets to clump together at the site of the tear with subsequent formation of a blood clot blocking the heart artery.

Anti-platelet drugs are routinely given to patients with severely narrowed heart arteries – those with heart attacks, those who have undergone insertion of stents into heart arteries, those with heart bypass surgery and those with strokes due to blocked arteries.

The second group of drugs, anticoagulant drugs, act on a different blood clotting mechanism which is activated through proteins, called blood clotting factors, which are mainly produced by the liver. This is given to patients who are at risk of spontaneous blood clot formation as a result of abnormal heart rhythm (such as atrial fibrillation), severe damage to the heart pump or artificial mechanical valve replacement.

Signs of bleeding

Early signs of thinning of the blood include easy bruising on the skin and gum bleeding. More serious bleeding will usually involve the gut. Bleeding from blood thinning agents can arise from the stomach or the small intestine and it can either present as vomiting of blood (which may be fresh red blood or altered blood that looks like coffee) or stools which are almost black in colour (as a result of altered blood). It can also present as passage of dark red or fresh blood in stools as a result of bleeding in the large intestine.

Risk of bleeding

Based on data published by US researchers from Mayo clinic in September in the Circulation journal on patients of age 60 years and above, the overall incidence of stomach or upper small intestinal bleeding with use of blood thinning drugs was about two in 100 patients who were followed up for one year. The overall incidence of bleeding from the large intestine was about seven per 100 patients who were followed up for one year. The risk was highest in those who were on anti-platelet drugs and anticoagulant drugs together. Those on this combination were also most likely to require hospitalisation and to require blood transfusion, especially if aspirin was the anti-platelet agent being prescribed.

For every 100 patients who are started on a combination of aspirin and an anticoagulant drug for the first year, there will be about two who will have bleeding from the stomach or upper small intestine, almost seven who will bleed from the large intestine, three who will require hospitalisation, and about six who will require blood transfusion. The numbers are slightly better if aspirin was replaced with another anti-platelet drug when used in combination with an anticoagulant drug.

The use of two antiplatelet agents (aspirin plus another antiplatelet agent) is the routine medication for all patients who have just had stents placed in their heart arteries to open up blockages. For every 100 patients started on this combination for the first year, about one will have bleeding from the stomach or upper small intestine, about six will bleed from the large intestine, 1.5 who will require hospitalisation, and about two who will require blood transfusion.

Hence, it is clear that the use of long-term blood thinning agents is associated with significant risks of bleeding from the gut.

Do all blood thinning agents damage the stomach and intestine?

Aspirin, even at a low dose, doubles the risk of a major bleed compared to those given a placebo. Aspirin can cause direct injury to the lining of the stomach and intestines, resulting in bleeding. Unlike aspirin, the other blood thinning agents including the other types of anti-platelet drugs (such as clopidogrel, prasugrel, ticagrelor), and anticoagulant drugs (such as warfarin, rivaroxaban and dabigatran) do not directly injure the lining of the stomach and the intestines but will increase the likelihood of bleeding if there is damage to the wall lining.

Precautionary measures

There are several precautionary measures to take when taking blood thinning drugs. First, do not take aspirin for prevention of heart attack if you do not have significant heart disease. There is no definitive evidence that aspirin is effective for the prevention of heart attacks for those who have never had a heart attack. This is so even for those with known heart disease but with no prior heart attack.

There is evidence that microscopic vessels in the wall of the heart arteries can bleed into the narrowed segments of the heart artery and worsen the heart condition. Aspirin can potentially predispose to this in those with pre-existing narrowing of the heart arteries. In addition to the risk of bleeding from the stomach and gut, aspirin can cause serious bleeding into the brain. In a review of the role of aspirin in heart disease published earlier this year in the European Heart Journal, the author concluded that there was no reliable evidence that aspirin used in the current fashionable doses of 50-100 mg/day is of any benefit in any common clinical setting.

Second, if long-term anti-platelet drug treatment is necessary, another alternative antiplatelet medication (such as clopidogrel) can be considered in place of aspirin. Third, underlying medical conditions that can predispose to bleeding in the gut should be treated, including gastritis, ulcers, and piles. Fourth, drugs that reduce acidity and protect the stomach and the upper small intestine from bleeding should be given to those who require long-term blood thinning medication.

Fifth, for those who have an increased risk of bleeding because of age or underlying medical conditions or may require surgery in the future, when undergoing stenting of their blocked heart arteries, they should consider the use of the new generation of heart stents which do not require long-term blood thinning medication (usually not more than six months) as opposed to older generation of stents which require lifelong anti-platelet medication.

Sixth, when starting oral blood thinning drugs, avoid drugs that can increase the risk of bleeding in the gut such as painkillers under the group of non-steroidal anti-inflammatory drugs (NSAIDs), steroids, anti-depression drugs called selective serotonin reuptake inhibitors (SSRIs) and injectable blood thinners called heparin.

Seven, if you are on warfarin, you will need to understand the multiple food and drug interactions with this drug and the risk of foetal abnormality when becoming pregnant while on medication. Finally, wherever possible, try to avoid having to take anti-platelet drugs and anticoagulants together.