Silence is golden. But this may not be entirely true for the heart, especially in the case of diabetics. Around 10 to 12 per cent of all heart attacks come silently, without any premonitory symptoms. And double this level is noted in the case of diabetics. There are around 160 million people across the globe suffering from diabetes mellitus (DM). Approximately 40 per cent of them have coronary atherosclerosis, which is fat deposition in the arteries supplying the heart muscle. These are the patients who are prone to having heart attacks. The epidemic of DM has left cardiologists with the challenge of identifying those diabetics who are at high risk of silent heart attacks.
Why are heart attacks silent in diabetics? Diabetics have an altered pain threshold owing to damage that has occurred to nerves that convey the pain sensation. Some of them may experience unexplained sweating, extreme fatigue or breathlessness. Sometimes premonitory symptoms may be underplayed because of psychological denial. Many diabetics have non-critical (less than 50 per cent blocks) diffuse fatty plaques in blood vessels without significant obstruction to blood flow. Since the blood flow is still maintained, they may not have any symptoms. But the plaque can suddenly rupture, making the vessel prone to clot-formation. The super-added clot can completely block blood flow and result in a heart attack. The first symptom in some diabetics can be a massive heart attack, or even sudden death before they can seek any medical help.
Why are diabetics prone to having such heart attacks? Abnormal glucose metabolism results in altered fat metabolism, causing high levels of bad cholesterol. Usually there is a clustering of risk factors such as obesity and high blood pressure. These factors result in early deposition of fat on the walls of the arteries supplying the heart: this is atherosclerosis. In diabetics, atherosclerosis occurs early in life and progresses to advanced forms. This condition affects blood supply to many territories such as brain, heart, limbs and kidneys. Moreover, in diabetics the fatty plaques have thin caps. These rupture easily, making them prone to heart attacks.
In the case of most diabetics, blood vessel, or vascular, damage has already begun by the time it is detected. The root cause of vascular damage is insulin resistance. (Insulin is the hormone that controls blood sugar levels.) This happens years before DM manifests itself. In the case of many diabetics, by the time coronary artery disease (CAD) is detected it is in an advanced stage, with the pumping function of the heart impaired. Many of them may not even be ideal candidates for balloon angioplasty (PTCA) or coronary artery bypass graft surgery (CABG), which are the procedures that are carried out to improve blood flow to the heart.
Early diagnosis is the key to preventing silent heart attacks. There are non-invasive tests such as stress electrocardiography (the treadmill test) or stress echocardiography which can help detect CAD early. Routine screening of carotid artery (the blood vessel supplying the brain) intimal medial thickness may provide an indirect assessment of vascular damage. There are some special tests like stress nuclear perfusion scans for use in selected cases.
The availability of CT coronary angiography in the last five years has made it possible to diagnose non-invasively the nature and extent of blocks. It also provides information on the characteristics of fatty plaque, such as soft, hard or calcific (soft plaque being more prone to rupture). Initially 64-slice and now 320-slice CT coronary angiography is available, which gives better-resolution images within a few seconds with reduced exposure to radiation. This is the best non-invasive modality for the detection of pre-clinical atherosclerosis.
A test in time
The saying that a stitch in time saves nine could be adapted to read: a test in time saves thine (your heart).
Once a high-risk individual is identified, aggressive preventive measures are advised. To quote from Shakespeare in Hamlet: “Where the offence is, let the great axe fall.” The offence here constitutes fatty plaque, and the axe is a triad comprising lifestyle changes, strict control of DM and control of other risk factors.
Lifestyle modification includes dietary discipline with the consumption of fresh vegetables, a low carbohydrate and high-fibre diet, weight reduction, stoppage of smoking, moderation in alcohol consumption and regular exercises. Yoga and meditation helps reduce stress levels.
Proper blood sugar control is essential. Recent studies have revealed that coronary events are more common during hypoglycemic attacks (where the blood sugar level drops). Strict supervision by a diabetologist is mandatory.
The control of other risk factors is equally important. Blood pressure should be well under control, with the target level being 130/80 mmhg, to prevent vascular and renal complications. Diabetics are prone to having high bad cholesterol levels (LDL&TGL) and low good cholesterol (HDL) levels. In addition to a low-fat diet and regular exercise, they need cholesterol-lowering drugs such as statins. Blood thinners such as aspirin and drugs to prevent vascular complications are also routinely prescribed. Once asymptomatic CAD is diagnosed, aggressive treatment will ensure prevention and help postpone the onset of any complications.
The intention here is not to create fear in the minds of diabetics, but give a wake up call. Diabetics: wake up, it is never too late.
( Dr. I. Sathyamurthy is an interventional cardiologist who is the director of the Department of Cardiology at Apollo Hospitals in Chennai. He received the Padma Shri in 2000, the Dr. B.C. Roy National Award in 2001 and a D.Sc (Honoris Causa) conferred by the Dr.M.G.R. Medical University in 2008.)