Magnetic resonance imaging can now be used to predict the risk for a fast and dangerous heart rhythm known as ventricular arrhythmia. Patients whose muscle wall thickness contained over 25 percent of scar tissue are nine times more likely to likely to test positive according to researchers at Johns Hopkins Institute.
If the findings can be extrapolated to accurately predict the risk of arrhythmia-related sudden death, MRI could soon turn out to be a gold standard in the screening of high-risk cardiac patients. It can even determine the need for the placement of a defibrillator in such individuals.
A defibrillator is a device that restores the normal cardiac rhythm following an arrhythmia by delivering an electric shock. It is usually prescribed in patients with a poor ejection fraction and/or with those resistant to the electrical impulses designed for simulation of arrhythmia.
The study is the first to analyze the architecture of the heart for clues about arrhythmias in patients with poor heart function but no arterial disease. While tests are widely available to screen patients with coronary artery disease for risk of sudden cardiac death, tests are not so effective for identifying the many who will die suddenly from arrhythmias.
Twenty-six patients with an average age of 53, referred for cardiac assessment with symptoms such as such as shortness of breath, instant fatigue and the inability to walk up stairs were taken up for the study.
The amount of scar tissue was measured as a percentage of the thickness of the muscle wall, which is on average about 1 centimeter. Composed of dense, fibrous tissue, with little to no blood supply, scar tissue was clearly visible on the image.
Statistical analysis showed that the five patients who tested positive had the characteristic scar pattern, ranging from 26 percent to 75 percent scar tissue, with MRI. It is believed that history of inflammation; injury or excessive stress to the heart may contribute to scar formation.
Cardiac MRI is already useful for assessing the structure and function of the heart and the extent of structural changes due to coronary artery disease. MRI can also help identify patients in need of aggressive medical therapy and can help in the planning of invasive heart surgery or identification of the best candidates for bypass surgery.
Another potential application is in the identification of the characteristic scar pattern that could potentially improve existing procedures to ablate, or burn off, regions of the heart muscle that trigger arrhythmia.
The non-invasive nature of the investigation, accompanied by significant reduction in the incidence of infection and the ease of performance add to the credit of the MRI technique over the other options available.