By Penny Stern, MD
NEW YORK, Oct 01 (Reuters Health) -- For over two decades, the treatment of heart attacks has focused on restoring the impaired blood flow to the part of the heart affected by blockage of a coronary artery. But study results published in the October issue of the Journal of the American College of Cardiology now suggest that heart attack does not just involve the blood flow in one vessel, but rather blood flow throughout the entire heart.
"Heart attack is a global process -- throughout the heart -- and not just a problem involving one artery," study lead author Dr. C. Michael Gibson, of the University of California at San Francisco told Reuters Health.
Gibson said that he was "surprised" at these findings. "We had always used the (apparently) uninvolved artery as a kind of 'gold standard' in measuring blood flow (in the heart)." Yet when angiographic film footage was analyzed by the investigators, they found that in fact, "heart attack (seems to) affect all three (major arteries) that supply the heart."
"We found that these 'uninvolved' arteries are not normal; (blood flow in them) is actually slowed down by about 45%," Gibson continued. "So for years, we had been grading the main (involved) artery against the (assumed to be normal) other two arteries. But the 'gold standard' we were using wasn't really gold -- it was kind of a tin standard, it seems," he noted wryly.
The researchers measured the time it took for dye injected into the heart to reach portions of the artery beyond the blockage. "Normal would be 21 frames (on angiographic film)," according to Gibson. "Even (after treating the blockage), you don't get all the way back to normal. You get back to about 30 frames, so you're still 9 frames away from normal."
Using these data, Gibson and colleagues, who are part of the Thrombolysis in Myocardial Infarction (TIMI) Study Group, determined that there seems to be a kind of 'speed limit' in the heart when it comes to blood flow. He explained to Reuters Health, "We found that if you blow up an (angioplasty) balloon in the coronary artery blockage, normal flow is not restored. You are only able to restore flow (to the same degree) as in the two uninvolved coronary arteries -- and both of those are slowed down, as we now know, by about 40% to 45%."
Though conventional treatment for blockage in a coronary artery often involves the use of balloon angioplasty or the placement of stents (tubes to keep the vessel open), Gibson believes that "we also need to treat smaller vessels that are downstream from the major (involved) artery so that blood flow throughout the heart speeds up, (because) it's these small resistance vessels downstream that... probably slow the flow down, even after you get rid of the blockage."
For people who are treated successfully for a blockage yet still have evidence of reduced blood flow, the consequences can be severe. "If you have normal flow after treatment for a blockage, mortality is under 1%. If you have abnormal flow, your risk of dying is up around 10%," Gibson said. "The people who have slower flow are... also at higher risk of having another heart attack or having poor pumping action of the heart, so flow throughout the heart is clearly related to worse outcomes," he added.
The type and location of heart attack is also a prognostic factor because "in an anterior myocardial infarction -- a heart attack in the front part of the heart wall -- those blockages tend to be much closer to the beginning of the artery and you end up having a 'bigger' heart attack. A bigger heart attack also puts you at risk for having this reduced global blood flow," Gibson said.
Gibson and his team are currently involved in studies looking at the use of the new 'super-aspirins' in conjunction with thrombolytic (clot-busting) agents. "We've now been able to show that we can break through that 30-frame speed barrier by giving 'super-aspirins' along with the (thrombolytics)." He notes that "this kind of combination therapy (involving) inhibiting platelets and keeping them from plugging up the microvasculature (small vessels)" may prove helpful in preventing the impaired global flow phenomenon.
