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| May 22, 2000 | ||
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| CARDIOGRAPHY Heart Warning Now comes a revolutionary diagnostic tool that picks up early cardiac symptoms By Sumit Mitra
The diagnostic methods in practice -- like the treadmill test that measures heart impulses at progressive stages of exercise -- are notorious for giving what doctors call "false negatives". The "gold standard" of detecting coronary disease is, of course, angiography, where a cardiac catheter is inserted through the patient's groin and subsequently an iodine-based dye is injected into the coronary arteries. This gives a road map of the obstructions. But that's an invasive method. Scientists looking for a reliable and non-invasive diagnostic tool have long been eyeing the machines that are routinely used to detect wounds or warts in static organs, like the computerised tomography (CT) scan and the magnetic resonance imaging (MRI) machine. These machines, however accurate, are nevertheless too slow for the heart -- like a pin-hole camera trying to capture a cricket ball in flight. All that is about to change. GE Medical System has devised a unique combination of a cardiovascular MRI and a fast ct scan, both geared to take high-speed sectional images of the heart. The combo, worth close to $3 million (Rs 13.2 crore), is installed in just about a dozen centres in the world, including the National Institute of Heart, Bethesda, US, Stanford University and Keio University in Japan. Escorts Heart Institute and Research Centre (EHIRC) in Delhi is one of the centres to acquire the machine that may dramatically alter the detection of early symptoms of coronary vascular disorder. "On May 15 we are going to inaugurate the unit after much research," says EHIRC Executive Director Naresh Trehan, "and we are sure it will revolutionise early detection techniques." The heart MRI, like all magnetic resonance imagers, works on the principle that the hydrogen ions of the body, first aligned in a magnetic field and then given yet another magnetic push in a different direction, should return to the previous alignment after the extra push is withdrawn provided there is irregularity in the tissue. However, the speciality of the new machine is, in the words of Dhan Raj Jangid, the institute's senior consultant in cardiac imaging, "designed to trap the heart in time". The time-trapping is possible through the combination of an ultra-strong magnetic field (1.5 Tesla), which is 25,000 times stronger than the earth's magnetic pull, and a high-powered Silicon Graphics array processor that crunches the data on the ions at a mindboggling speed -- making 10,000 million trillion interpolations each second. The result is a composite "picture" of the heart in 10-20 milliseconds, which, the doctors at the institute say, is enough "shutter speed" to snap the inside of the ever-moving organ, slightly larger than a clenched fist. "In these images," says EHIRC cardiologist Sameer Shrivastava, "we look for the odd patterns of the hydrogen ions' recovery to the pre-aligned position. If there is patch where the ions are slow to get back to where they had been, that could surely be an obstruction in the making." Patients wake up to the problem of clogged coronary vessels after 70 per cent of one of the arteries is choked. By the time the first stab of chest pain is felt, caused by insufficient blood supply to the heart muscle, or ischaemia, one or two coronary vessels may have narrowed by half or more. However, cardiovascular MRI, capable of presenting three-dimensional data, is capable of picking up a "stenosis", or the narrowing of a vessel, when it has just hit the 10-per cent mark. From the highly magnetised MRI chamber (patients with rods and other steel implants in their body, beware!), the action shifts to the fast ct scan tunnel. There the machine takes fast counts of calcium in and around the heart, more calcium meaning more chance of a plaque buildup. While a normal ct scan takes stationary calcium profiles, the cardiac variety slices up coaxial frames, at the rate of 10 frames in a single cardiac cycle of 0.8 second. Says Trehan: "The ct scan would show the presence of calcium even at the 20-30 per cent stage; and with MRI, we could even peep into a artery to see where it is narrowing." A conventional ct scan, together with the MRI test, costs around Rs 15,000. However, EHIRC plans to keep the tab low, at the cost price of Rs 9,000, "to raise awareness", as Trehan says. The benefit of an early finding of the hardening of a coronary artery is that it can be reversed by some determined lifestyle changes. That is an eminently affordable insurance against the cost, anxiety and agony of an open-heart surgery later in life. |
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Nobody
wants his heart to miss a beat -- well, not ordinarily. Yet his
cardiologist would certainly wish that to happen. For it is the incessant
dup-lub convulsion of the heart, 80 times a minute for human adults, that
makes the cardiologist's job of mapping the blood-pumping organ's inner
wall such an arduous task. The pulsation makes it particularly difficult
to read the "plaques", or the little hillocks of fatty material
deposited on the inner walls of the three coronary arteries that bring
oxygen and nourishment to the heart. More than anything else, it is the
plaque formation that holds the secret of myocardial infarction, arguably
the developed world's largest killer and, in India, the No. 1
non-infectious fatal disease.