Cardiac Imaging Advance Helps Determine Diminished Blood Flow to the Heart

Research is challenging the classic paradigm used to determine whether heart patients will benefit from invasive procedures such as stent-placement or open-heart surgery.

Current medical practice favors treating patients with coronary atherosclerosis with such procedures if a coronary artery is shown to be blocked by 70% or more in order to reduce symptoms and potentially prevent a heart attack. However, a group of cardiac investigators is now finding that in addition to the level of blockage, composition of the plaque causing the blockage also has significant impact on coronary artery blood flow. This may help clarify why two people with similarly blocked coronary arteries can experience vastly different symptoms.

"If we can determine certain characteristics of the coronary artery plaque, we can predict whether a patient's symptoms are due to limitation of blood flow to the heart,” said Haim Shmilovich, M.D., principal author of the study and a cardiac computed tomography/magnetic resonance imaging (CT/MRI) fellow-cardiologist at the Cedars-Sinai Medical Center (Los Angeles, CA, USA). "With further studies, our findings may change treatment planning for patients with severe but stable coronary artery disease by helping us determine which patients could be treated just as effectively with medications and lifestyle changes, thereby avoiding unnecessary invasive angioplasty and bypass surgery.”

Dr. Shmilovich and colleagues used two imaging procedures: coronary CT angiography (CCTA), which reveals the composition of coronary artery plaque and the degree of blockage it causes, and myocardial perfusion imaging (MPI), which measures relative blood flow to different regions of the heart. The investigators discovered that clinicians can more accurately determine a patient's risk of having reduced blood flow to the heart muscle by identifying three plaque characteristics: the presence of a fatty core, signs of spotty calcifications, and enlargement of the arterial wall from "positive remodeling,” which means the body has responded to arterial damage by altering the structure of the artery. Either individually or combined, the presence of these characteristics in diseased arteries can predict diminished blood flow to the heart muscle, which could lead to symptoms, including heart attack.

For this study, 34 patients without known coronary artery disease were imaged using CCTA and MPI to determine the presence of adverse plaque characteristics (APCs) and blood flow. Length of time between scans was limited to six months without any interval change in patients' symptoms or treatment. All patients had severe (70% - 89%) blockage in the beginning or middle section of a major coronary artery on CCTA. APC evaluation on CCTA was performed by a blinded third-party specialist, and MPI assessment was conducted through automated computer-based validated analysis.

The study's findings indicated that slightly more than 38% of all patients had significant ischemia, i.e., considerably limited blood flow to the heart muscle, when imaged with MPI. In the arteries with plaques that showed a fatty core, significant ischemia of the heart muscle portion nourished by the affected artery occurred at a much higher and statistically significant frequency (80%) than those without a fatty core (21%). Finding multiple APCs in a plaque was also associated with higher degrees of significant ischemia.

The research was presented at the Society of Nuclear Medicine's (SNM) 57th annual meeting, held June 5-9, 2010, in Salt Lake City, UT, USA.

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