Coronary heart disease is the nation’s No. 1 killer; 6 million Americans currently suffer from it, and 1.5 million will have heart attacks this year. Exercise ECG, the noninvasive “stress test” that measures electrical impulses produced by the heart as it contracts, accurately detects a past heart attack, or one in progress. But ECG is less reliable when it comes to identifying the earlier stages of coronary heart disease, especially in women. Possibly because their hearts are smaller, the accuracy of ECG can drop below 50 percent for women.
Unlike ECG, seismocardiography measures the mechanical activity of the heart, primarily the pumping action of the left ventricle as it supplies oxygenated blood to the body. The technique was developed by John M. Zanetti, a California seismologist who now lives in Minneapolis, and Dr. David M. Salerno, a cardiologist and director of the ECG lab at Hennepin County Medical Center in Minneapolis. If a seismograph placed on the earth’s surface could detect vibrations deep within, Zanetti reasoned, why couldn’t it be placed on a patient’s chest to measure cardiac activity?
After initial tests showed promise, the researchers raised enough money to fund a study of 1,200 patients at the Minneapolis Heart Institute. The combination of ECG and SCG detected heart disease in 88 percent of those patients who were subsequently proved to have it through more elaborate diagnostic tests-including 86 percent of the women. Similar results from a second study of 600 patients at five medical centers will be announced this week.
The device that performs seismocardiography was approved by the Food and Drug Administration in 1989; 11 of them are currently on loan to practitioners who are evaluating their usefulness. While those who have used the technology agree that it needs further testing to confirm its reliability, they are impressed by its potential. “It will raise the confidence level for saying that the disease is present or absent,” says Dr. Virinderjit S. Bamrah, chief of cardiology at the Veterans Administration Medical Center in Milwaukee. SCG is safer and less expensive than a number of other more elaborate tests currently used to diagnose heart disease. If its initial promise is confirmed, earthquake technology will take its place among the arsenal of weapons doctors use to fight a different kind of catastrophe.
These wave patterns both show the heart at rest. Seismocardiography picks up vibrations from the beating heart; electrocardiography measures the electrical impulses it produces.
