Cardiovascular diseases (CVDs) are the leading cause of mortality in India, accounting for nearly a fourth of all mortalities. Ischaemic heart disease—reduced blood flow to the heart via the coronary arteries—and stroke are the dominant cause in all CVD deaths, accounting for more than 80% of such deaths. Given the rising CVD burden in India, the focus has been on medical devices such as stents that are used to treat arterial narrowing due to sclerosis. But the spotlight on stents and other medical devices has been mostly due reasons of pricing—stents have for some months now been put under a price-control regime. Thanks to this, there has been little to no attention on the technological advancements.
With atherosclerosis a prime cause of ischaemic heart disease, stents have taken centre stage. Over the years, stent technology has moved from plain metal stents to drug-eluting stents to, now, dissolvable stents and drug-filled stents. Formation of local clots where the stent is placed has been a hazard with all stenting. To that end, stents exhibiting dissolution or bioresorbable stents got approval last year. Made of polylactic acid, a dissolvable substance, these stents take care of the thrombosis (clotting) and restenosis (recurring narrowing of the blood vessel) associated with older forms of stenting. Dissolving in two years, these restore the vessel to its natural state of vasoconstriction and vasodilation. But, a paper published in the New England Journal of Medicine warns that bioresorbable stents may not be all that they are cracked up to be. In its most recent clinical trial, the first bioresorbable stent to be marketed was linked to an increase in risk of device thrombosis, where the clot forms on the stent itself. While device thrombosis was noticed in just eight patients with drug eluting stents, it was noticed in 31 patients who had the bioresorbable stent.
Drug-filled, zero-polymer stents address the risks associated with bioresorbable stents and simple drug eluting stents by achieving controlled and sustained elution of drugs, thereby shortening the duration of the dual anti-platelet therapy that are prescribed with stenting to keep vasodilation at the optimal level.
Valve impairment is a big concern in India, too. Of the four valves in the heart—these collectively regulate pathway of blood inside the heart—the aortic and the mitral valves are the ones that mostly need replacement due to impairment. Treatment has come a long way from reliance on mechanical valves, the traditional replacement therapy. Now, tissue valves, including those from porcine (pig) and even bovine (cattle) pericardia are being used, especially in patients put at risk by long-term anti-coagulation treatment that often accompanies replacement with mechanical valves. With advanced anti-calcification therapy, the tissue valves offer the same benefits as mechanical valves—better endurance and superior haemodynamics. Bovine tissue valves that don’t require suturing are now being preferred for minimally invasive surgeries.
Another newly developed method—approved circa 2012 in the US—opted for in cases of patients who carry risks forbidding surgery is Transcatheter Aortic Valve Implantation (TAVI) is another procedure in which the replacement aortic valve is placed through a catheter inserted into a blood vessel. This used to treat cases of aortic stenosis (or the narrowing of the exit of the left ventricle, at the aortic valve). Rheumatic fever, which is responsible for 25-45% of acquired heart disease, often leads to aortic stenosis. Given how endemic it is—a ICMR study puts its prevalence at 6 out of 1,000 in children in the 5-16 age group—TAVI is a procedure that is likely to gain ground. Globally, more than 200,000 patients have received TAVI, and in several clinical trials, like in the US, it has shown better results than surgical valve replacement.