What Causes Sudden Heart Attacks?
A New Look at Sudden Heart Attacks with a profile of Steven Nissen, MD
We’ve all heard the stories. It may have happened to someone you know or love. A perfectly healthy person. No sign of coronary artery disease. Sometimes the victim has only recently passed a stress test, or had an angiogram that showed no arterial blockage. Then one day without warning: a sudden fatal heart attack. Like a hammer from heaven.
What could have caused it? For decades, it has been accepted that most fatal coronary events are a consequence of the narrowing of the coronary arteries caused by the gradual buildup of hard, fatty plaque on the artery walls. Angiography, atherectomy, and coronary artery bypass grafting are diagnostic and therapeutic procedures designed to detect and treat this condition before it becomes fatal.
The accepted wisdom, however, may be wrong. New imaging techniques are verifying that the greater risk of heart attack comes from another type of plaque: soft fatty deposits that build up inside (not on) the walls of the coronary arteries. Hidden in the artery walls, covered by a thin, fibrous cap, these unstable plaques don’t narrow the artery or lessen the flow of blood. But they do get infected. And sometimes the fibrous cap that holds them in place breaks. That’s when the heart attack begins.
When the cap ruptures, the soft infected plaque oozes out. A massive blood clot suddenly forms at the site of the rupture. Within seconds, the artery is fully and efficiently blocked. No blood gets to the heart muscle. Result: Myocardial infarction.
“The new message is that most of the plaques involved in coronary artery disease are not the plaques that significantly narrow the artery,” says Steven Nissen, MD, vice-chairman of Cardiology, and head of Clinical Cardiology “Only one in seven heart attacks is caused by a blockage of more than 70 percent.”
The most dangerous part is hidden. Most diagnostic tests detect the presence of plaque by its effect of narrowing the arteries. But since vulnerable plaques narrow the artery little if at all (up until the moment they rupture), angiograms, echocardiograms or stress tests don’t detect them. “It’s the classic tip of the iceberg problem,” says Dr. Nissen. “We’ve become facile at treating the tip of the iceberg. But the most dangerous part is still below the surface.”
To detect vulnerable plaque lurking in the artery walls, Dr. Nissen uses a technique called intravascular ultrasound (IVUS). Developed over the past decade, IVUS consists of a miniature sonar-type device at the tip of a catheter. When inserted into a patient’s coronary arteries, it sends back a cross-sectional image of the artery walls. It reveals not only the presence of vulnerable plaque, but shows how thick, or thin (and possibly unstable) is its cap.
Unfortunately, IVUS and other imaging techniques that reveal vulnerable plaque are impractical for use in routine examinations. So vulnerable plaque remains difficult to detect, and therefore not easily treated by atherectomy, stenting or bypass. For this reason, there is a particular urgency to verify the effectiveness of drugs that can halt or reverse these plaques’ dangerous tendencies
National clinical trials. Dr. Nissen is leading two nationwide clinical trials to test the effectiveness of cholesterol-lowering drugs in neutralizing vulnerable plaque. The first trial, called NORMALISE compares two calcium-channel blockers used to treat angina and heart blood pressure. The second trial, called REVERSAL, compares the effectiveness of two cholesterol-lowering drugs vs. vulnerable plaque. As its name implies, this study hopes to show that these drugs cannot only neutralize, but actually reverse the development of vulnerable plaque.
“We can reduce angina [chest pain] through angioplasty and stenting,” says Dr. Nissen. “But those techniques do not reduce the chance of death by heart attack.” Dr. Nissen believes that cholesterol-lowering drugs are the best current defense against the danger of vulnerable plaques. Fortunately, the life-style recommendations traditionally advised for the prevention of heart disease are no less effective against vulnerable plaque. That is: to quit smoking; get regular exercise; and eat a diet low in fats, and high in fruits, vegetables and fiber.
“What you see here is a shifting of thinking from a preoccupation with hard plaque that narrows the arteries, to a focus on the dangers of vulnerable plaque,” says Dr. Nissen. “We’ve come to this point over a number of years. In the beginning, only a few people giving it much attention. Now it’s become a torrent.”
Profile: Dr. Nissen and IVUS
In 1988, cardiologist Steven E. Nissen, MD, got a phone call that changed his life. It was from a small company that was developing a new technology for looking inside of blood vessels: Intravascular ultrasound, or IVUS. They thought Dr. Nissen might be interested in IVUS. He had published articles on the limitations of angiography, the then-gold standard for viewing and diagnosing coronary artery disease. IVUS promised to surpass angiography, and provide a moving, real time image from inside the blood vessels themselves. “It was something completely new,” says Dr. Nissen. “I made a decision on the spot that this was a great idea.”
Where angiography shows a two-dimensional silhouette of the interior of the coronary arteries, IVUS shows a cross-section of both the interior, and the layers of the artery wall itself. Over the next ten years, Dr. Nissen has been a leader in the development and application of IVUS to the diagnosis of coronary artery disease and use in the research into its causes and treatments.
IVUS was the first imaging technique to reveal the full extent and danger of vulnerable plaque (see article above), the substance now believed to be responsible for most sudden fatal heart attacks. Dr. Nissen is a strong advocate of aggressive pharmacological therapy in attacking these plaques. “Cholesterol lowering drugs may be able to reduce the likelihood of a vulnerable plaque rupturing by 50 to 80 percent,” he says. “Risk factor management, including the reduction of serum lipids, should be the goal in virtually every patient at risk, with or without coronary artery disease.”
REVERSAL, a national clinical trail he led using cholesterol-lowering drugs against vulnerable plaque demonstrated a medical first: The actual regression of atherosclerotic disease.
In respect to this, Dr. Nissen likes to quote the ancient Chinese book Nei-Jing that the effect that the superior doctor prevents the disease, the inferior doctor treats the diseases once it is already underway. “But the best doctors,” he adds in his own view, “reverse the disease.”
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