Questions from the heart

LAST week, I gave a talk on ensuring a healthy heart at a public symposium organised by The Business Times and Mount Elizabeth Novena Hospital. The responses to some of the common questions from the public are captured in this article.

I exercise daily and have good control of my cholesterol levels. Why is it that I still get blockage of the heart arteries?

Studies have claimed that 40 per cent to 60 per cent of susceptibility to heart artery disease is inherited. Data from the Framingham Study and the INTERHEART studies have shown that a family history of heart artery disease is associated with a 1.5 to >2 times increased risk of heart artery disease. A genetic risk variant identified that is associated with increased risk of heart attacks is located at the ABO blood group genetic site. In the Nurse's Health Study on more than 90,000 patients followed up for 20 years, the presence of blood group A or B was each associated with a 10 per cent increased frequency of heart attacks and the risk was increased about 20 per cent for those with both A and B blood groups. Those with A and B blood groups produce a protein that modifies the blood clotting factor termed von Willebrand Factor (vWF) thereby increasing the duration in which it remains in the blood stream and hence the level of vWF is about 25 per cent higher in those with blood groups A, B and AB when compared to those with blood group O. As the main mechanism of heart attack is the formation of a blood clot which then obstructs the residual lumen of the narrowed heart artery, increased levels of blood clotting factor will increase the probability of blood clot formation and thereby increase the likelihood of a heart attack. In addition, it has been estimated that production of about 3/4 of the HDL ("good") cholesterol and LDL ("bad") cholesterol is determined by the genes in our body. In some, the genetic variation may cause the patient to be less responsive to cholesterol lowering drugs (statins) and hence, the LDL cholesterol cannot be significantly lowered even with high dose statins.

By consuming drugs and supplements which can increase the HDL (high density lipoprotein) 'good' cholesterol, can I reduce my risk of a heart attack?

While most of us have been led to believe that HDL cholesterol is beneficial and high HDL cholesterol will reduce the risk of a heart attack, more recent evidence does not show this to be so. HDL is not one single complex but comprises a spectrum of fat and protein complexes some of which hardly contain cholesterol. HDL is considered to have an important role in removing cholesterol deposited in the arterial wall but more recent studies have shown that a subtype of HDL has the reverse effect of bringing cholesterol from the blood into the arterial wall to be deposited. Four more recent high profile clinical trials of HDL-raising treatment (Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Outcomes; Heart Protection Study 2; Treatment of HDL to Reduce the Incidence of Vascular Events; Investigation of Lipid Level Management to Understand Its Impact in Atherosclerotic Events and the Dalcetrapib Outcomes Study) have shown negative results even when the HDL cholesterol levels were elevated 100 per cent. This led to a rethinking on HDL-cholesterol and experts caution against the pursuit of treatments focused on raising levels of HDL cholesterol. This was further reinforced by the publication in the highly regarded Lancet journal in 2012 of a study which showed that genetic mechanisms which increase HDL cholesterol do not seem to lower the risk of a heart attack.

What is considered as normal blood pressure?

The latest Eighth Joint National Committee (JNC 8) report on blood pressure recommends that for those 60 years or more, the blood pressure should be below 150/90 mm Hg. A target blood pressure level of 140/90 mm Hg or less is recommended for those less than 60 years of age without other major medical illness. This target is also recommended for those 60 years or more who have underlying diabetes mellitus or chronic kidney disease. For those less than 60 years, the lower blood pressure value (diastolic blood pressure) is more important and for those aged 60 years or more, the upper blood pressure values (systolic blood pressure) is more important. There are other types of blood pressure variation of which a common form is the "white coat" hypertension where the patient's blood pressure is always high at the clinic but is normal at home. Failure to recognise this may result in unnecessary medication and repeated dizzy spells. Home blood pressure monitoring can help the patient confirm that the blood pressure elevation is due to "white coat" hypertension, and no medication is required in this situation.

Is it possible to have no symptoms and yet have a sudden heart attack?

Studies have reported that one third to 70 per cent of those who develop a heart attack may not have typical chest pain symptoms in the period prior to the heart attack. Hence, heart attack is also called the silent killer. Studies have also shown that a significant percentage of the patients who have a heart attack do not have significant blockage of the heart arteries. In addition, the elderly and women with significant blockage of the heart arteries may present with atypical symptoms.

Is it safe to do an invasive angiogram of the heart arteries?

Angiogram (X-ray of arteries) involves the insertion of small plastic tubes into the groin or wrist arteries under local anaesthesia and the manipulation of these tubes till they reach the opening of the heart arteries. An iodine contrast dye is injected and images of the heart arteries are taken using X-rays. This is a commonly performed procedure for those who are suspected to have significant narrowing of the heart arteries. Although major complications such as clinical stroke, heart attacks and death from this procedure are extremely low, there are at least seven prospective studies to show that this procedure is associated with 5 to 22 per cent incidence of silent strokes. A study published by Patel in the New England Journal of Medicine showed that in the USA, out of more than 400,000 invasive angiograms of the heart arteries, about 39 per cent had normal heart arteries and only about 38 per cent were found to have significant narrowing of the heart arteries. Hence, the authors advised that alternative tests should be considered to reduce the likelihood of performing invasive angiograms in those with no significant blockage of the heart arteries.

Are there safer alternative ways to visualise the heart arteries without performing an invasive angiogram?

Over the last 10 years, the rapid development of Computed Tomography (CT) scan of the heart arteries has helped this three-dimensional "X-ray" of the heart arteries to become an alternative to the two-dimensional invasive angiogram. CT scan of the heart arteries is an outpatient, non-invasive procedure which is performed within seconds by an injection of contrast dye through the arm vein. In highly experienced centres, the procedure is extremely accurate and has a low radiation dose. Another alternative is the use of magnetic resonance imaging (MRI) of the heart arteries to scan the heart arteries. This technique can be performed without any X-rays and without any injection. It is very safe and is especially useful when assessing the young and women as it does not use any X-rays. The main limitation is that there are very few centres with the appropriate MRI machines and the experience to perform this test.

What are the secrets to long life?

Dr Lim is the medical director at Singapore Heart, Stroke & Cancer Centre. He is also the founding editor of "Heart Asia", a journal of the British Medical Journal Publishing Group. He has been appointed Emeritus President of Asia Pacific Heart Association and is currently the vice-president of both the World Chinese Doctors Association and the World Federation of Chinese Cardiovascular Physicians.

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

To read more of Dr Lim's previous health-related articles, please visit: http://www.btinvest.com.sg/specials/shscc