Even the most accurate tests do not predict with certainty whether a heart attack will occur, since it is difficult to predict which cholesterol deposit will rupture and whether a blood clot will form and block off the artery.
MARK Twain once said: "Be careful about reading health books. You may die of a misprint."
In the era of fake news on social media, it is important to separate myth from fact. As heart doctors, we often encounter some of these myths. Here are 3 common ones worth dispelling.
Myth 1: There’s one single “best” or ideal test for detecting coronary heart disease
There are many tests available for the detection of coronary heart disease (narrowing of the heart arteries), from a treadmill electrocardiogram (ECG) test to an invasive angiogram. Although it might seem obvious that one should just use the most accurate test available to rule out heart disease, in reality, each test has its strengths and limitations. Different tests also provide different types of information. Some tests, such as the computed tomography angiogram (CTA), are excellent at detecting the presence of anatomic narrowing of arteries.
There are other tests, such as the stress nuclear or stress echo test, which are useful to evaluate the functional effect of narrowing on blood flow. No single test routinely provides both these types of information, but often both are needed.
Expert international guidelines including the latest American College of Cardiology guidelines recommend considering patients’ symptoms, risk factors and their likelihood of developing heart disease when choosing a suitable test.
For patients with no symptoms, the guidelines recommend testing for risk factors such as high blood pressure, cholesterol, and sugar and managing them. Routine testing for heart disease with tests such as the CTA is not encouraged for these individuals. For patients with a very low likelihood of heart disease (for example, poking or musculoskeletal chest pain), the guidelines highlight that testing has limited value and often can be deferred. If needed, a treadmill test or coronary calcium scan can be considered.
For patients with chest pain and suspected heart disease, the latest guidelines favour using either stress imaging or a CTA. Both types of tests have their strengths and weaknesses. A CTA has higher sensitivity, while stress imaging is able to assess the effect of blood flow to identify which patients might benefit from intervention. Ultimately, choosing a test should depend on whether it can lead to better outcomes for the patient.
The largest trial, PROMISE, comparing CTA to stress imaging in 10,000 patients with chest pain, showed no difference in clinical outcomes (death, heart attack or hospitalisation) after 2 years of follow-up, suggesting that either approach is reasonable.
Myth 2: Routine heart scans can prevent heart attack
Given that heart attacks may occur suddenly, it is natural for people to think that it might be worth doing a heart scan to rule out the possibility of a blocked artery to prevent a heart attack, even when they have no previous symptoms. However, a number of studies have shown that screening for blockages in individuals with no symptoms does not seem to be effective at lowering the risk of a heart attack.
Two large randomised controlled trials to evaluate the routine use of screening tests such as CTAs or nuclear stress tests for asymptomatic diabetics showed no benefit in preventing heart attacks or cardiac events. There may be several reasons why this approach of screening does not seem to work, even when targeted at individuals with a higher risk of heart attack, such as diabetics.
First, focusing on prevention through risk factor control (blood pressure, smoking, cholesterol, blood sugar) may be more effective than relying on periodic scans. This is because narrowing of arteries can develop over time, and the absence of severe narrowing at the point of scanning does not mean the narrowing will not develop or rapidly worsen later.
Second, heart attacks are usually caused by a sudden blood clot triggered by a rupture or tear of a cholesterol deposit. It is the unpredictable rupture of the cholesterol deposit, followed by the sudden blood clot that blocks the entire lumen of the artery, which causes the heart attack, not just gradual narrowing.
Hence, even the most accurate tests to detect narrowing do not predict with certainty whether a heart attack will occur, since it is difficult to predict which cholesterol deposit will rupture and whether a blood clot will form and block off the artery. In some studies of individuals undergoing CT or invasive coronary angiograms, about half of all heart attacks later occur in narrowing that was not severe at the time of the imaging, and would not be subject to stenting, though it subsequently was the site of narrowing that caused the heart attack.
Third, ballooning and stenting of arteries can definitely improve symptoms, and lower the risk of heart attack in symptomatic patients with a recent or ongoing heart attack, but these carry a small risk of complications. While these small risks are well worth taking in the context of heart attacks, it might not be so for individuals who are well with no symptoms and are at low risk of a heart attack.
Some of these tests also involve a very small amount of radiation exposure, which is associated with very small incremental lifetime risk of cancer. The estimated additional lifetime risk of cancer due to radiation for a 40-year old man is low – about 1 in 1,500 for nuclear stress testing and 1 in 3,000 for a low-dose CTA – but this risk can add up if the tests are repeated periodically.
For patients with suspicious symptoms and a higher likelihood of heart disease, the benefits of such tests clearly outweigh these small risks. On the other hand, these tests should not be undertaken routinely for individuals who have no symptoms or are at very low risk of heart disease, especially if they are younger and radiation is a greater concern.
Finally, a ‘normal’ scan may give a false sense of security, leading the person to ignore risk factors such as smoking or high cholesterol. Conversely, an abnormal test may be a false positive result, leading to anxiety and more tests being done even when the actual risk is lower than it appears. Thus in individuals without symptoms, it is recommended to focus on risk assessment and prevention through a healthy lifestyle (exercise, diet, smoking cessation) and risk factor control (treating cholesterol, blood pressure, blood sugar), rather than to undergo screening that yields little or no benefit.
Myth 3: Blood thinners not needed for bioresorbable stents
Another false belief is the suggestion that newer coronary stents such as bioabsorbable stents do not require blood thinning medication. In fact, patients who received coronary stent implantation must take 2 types of blood thinning antiplatelet medicines for 6 to 12 months, followed by 1 for long-term maintenance. This is regardless of the type of metallic stent used.
Newer generations of metallic stents, because of their better healing characteristics, have enabled blood thinners to be temporarily interrupted 1 month after stenting if one has to go for unanticipated surgeries. However, medication will have to be resumed as soon as the bleeding risk is deemed acceptable.
It is dangerous to suggest that the implantation of bioresorbable stents can omit the need for all blood thinners after 1 year. This is because late clotting seen in such stents can result in heart attack and death, and this can still occur after 2 years.
It is noteworthy that some authorities even advocate continuing to take 2 blood thinners for up to 3 years. It is precisely because of this increased clotting risk that bioresorbable stents have fallen out of favour for use compared with metallic stents.