Heart attacks and angina are caused by blockages in the coronary arteries. These blockages restrict blood flow to areas of the myocardium (heart muscle) that are normally fed by the affected artery. This ?ischemia? reduces the oxygen supply to the affected tissue and also leads to a build-up of toxic metabolic by-products that are normally carried away by the blood. The solution to the problem seems obvious ? either unblock or bypass the artery, and restore blood flow. Many procedures are now performed to do exactly this, for example minimally invasive percutaneous coronary interventions (PCIs) that open up coronary arteries with balloons or stents.
However, in addition to PCIs and the more traditional coronary artery bypass grafts (CABGs) that directly address a blocked coronary artery, there are some exciting new devices that approach the problem from a completely different angle. These technologies are in fact based on a simple idea with a long history. Beginning in the 1920s and 1930s, experiments on lab animals suggested that, surprisingly, restricting blood flow through the coronary sinus (the main vein of the heart) actually reduced the damage caused by a simultaneous blockage of a coronary artery. Why is that? The best evidence suggests this is because reducing blood flow through the coronary sinus increases pressure on the venous side of the coronary vasculature, producing a ?backwash? effect of venous blood. This ?retrograde? flow of venous blood into the affected heart muscle is actually believed to deliver some oxygen and carry away metabolic by-products, thereby lessening the damage of blocked or narrowed coronary arteries.
So can this principle be applied to human patients? Two companies are currently developing devices to do exactly this. One is Miracor Medical Systems, which has developed the Pressure-Controlled Intermittent Coronary Sinus Occlusion (PISCO) system, designed for use in heart attack patients. This device consists of a balloon catheter that is introduced through the femoral vein to the coronary sinus, where it is periodically inflated during the first 1.5 hours after a PCI is performed to aid in the recovery of the myocardium. Another is the Reducer device from Neovasc, which is designed for stable angina patients, and which began an initial roll out in Europe recently. This device is a permanent implant in the coronary sinus, where again it functions to increase blood flow to the myocardium through partially blocking the coronary sinus, alleviating some of the symptoms of angina. Will these devices improve outcomes for both heart attack and angina patients and become a regular fixture of the cath lab repertoire? Time will tell; both devices are currently under investigation in clinical trials.