Electronic Stethoscope Shows Positive Early Results in CAD Detection

A novel digital, electronic stethoscope shows good early sensitivity and specificity in detecting coronary artery disease (CAD) compared with the gold standard computed tomographic angiography (CTA), according to a small study published online January 3, 2013, ahead of print in the American Journal of Cardiology. According to the authors, the device may represent a cost-effective noninvasive modality for outpatient CAD detection.

Researchers led by Amgad N. Makaryus, MD, of North Shore-LIJ Health System (East Meadow, NY), looked at 161 patients with no known CAD referred for cardiac CT imaging, comparing coronary CTA with the Cardiac Sonospectrographic Analyzer (CSA; Sonomedica, Vienna, VA).

Technology Detects Microbruits

The CSA consists of a stethoscope-like transducer attached to an amplifier and a portable computer. The system is designed to detect microbruits in the frequency range of 400 Hz to 2,700 Hz, characteristic of abnormal blood flow in atherosclerotic arteries marked by plaque. A computer algorithm helps generate a microbruit score of 0 (low probability of clinically significant disease) or 1 (high probability of clinically significant disease).

On CT angiography, 12% of the patients were CAD positive (> 50% narrowing in any 1 artery location). More men than women (14% vs. 8%) were classified as CAD positive, but the difference was not significant (P = 0.22). On logistic regression, the overall sensitivity and specificity of the CSA system for accurately predicting CAD compared with CT angiography (using a microbruit score threshold of 0.26398) was 89.5% and 57.7%, respectively. The results were statistically significant (P = 0.0007).

Gender-specific models showed a sensitivity and specificity with the CSA system of 85.7% and 50.6%, respectively, for men (P = 0.0008). For women, the sensitivity and specificity were 80.0% and 76.3%, respectively, but these results were not significant (P = 0.10), mainly because of the small number of women with disease.

In terms of traditional cardiac risk factors, patients over 60 years of age showed a higher likelihood of being positive for CAD according to the CSA system (P = 0.04), while there was no association with other  risk factors such as hypertension, dyslipidemia, or obesity.

The CSA exam was performed on each patient by sequentially placing the transducer over 9 positions on the chest and recording heart sounds for 40 seconds at each position. The typical recording session lasted 15 minutes, with acoustic and separately obtained ECG signals digitally recorded on the computer.

Potentially Cost-efficient Imaging Tool

“In conclusion, the CSA showed high sensitivity and specificity for the detection of significant early CAD in an outpatient setting and represents a new noninvasive device for detecting abnormal coronary blood flow as occurs in CAD,” the authors write.

The researchers note that the findings are highly relevant in today’s costly health care environment, in which cardiac imaging has contributed to the 4.8% growth per year in US health expenditures.

“The one avenue that has not been adequately explored or looked at is using the more cost efficient imaging tools to better stratify and diagnose the presence or absence of CAD or even be used as a first step to prioritize patients who may be recommended to go on to further imaging on the basis of the findings,” they say, adding that the CSA system fits this profile. “Application of this relatively cost effective (compared to cardiac imaging modalities) and efficient technique can help clinicians risk-stratify patients and make appropriate clinical decisions for management and potentially guide future therapy.”

In a telephone interview with TCTMD, Robert S. Schwartz, MD, of the Minneapolis Heart Institute Foundation (Minneapolis, MN), noted that “tons of people in the past have built digital stethoscopes, and they’ve never really been shown to be that much better than the ears.”

‘A Good Start’

Nevertheless, he described himself as “cautiously optimistic,” regarding the current study, adding that “the results are suggestive that there’s something here. ‘Convincing’ is perhaps too strong a word. All technologies have to start somewhere and this is a good start.”

Dr. Swartz noted that the technology would probably be most useful as a general screening tool. “We have plenty of great tools such as CT and other stress imaging for mid-level type testing. This can’t tell you how much CAD there is or where it is. This is more of a yes/no question that gets answered,” he said. “And if this was really good, you could envision this in a little booth in a mall someplace where people want to have their hearts checked. This would be one of the very first things that might be used because it’s cheap and easy, and there’s no radiation.”

However, the results may have suffered from selection bias, which contributed to the data looking “too good to be true,” Dr. Schwartz cautioned.

He explained that since the population was already referred for CT, there was a higher concentration of disease. In fact, almost half (47%) had at least 30% narrowing in at least 1 major coronary artery. “For people in your local mall, you would find a disease prevalence of 2%,” Dr. Schwartz said. “But here the results are a bit biased upwards in device performance because the prevalence of disease is so high. One in 2 patients had more than 30% narrowing, so you could’ve flipped a coin and gotten 50% sensitivity and specificity.”

 

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Source:
Makaryus AN, Makaryus JN, Figgatt A, et al. Utility of an advanced digital electronic stethoscope in the diagnosis of coronary artery disease compared with coronary computed tomographic angiography. Am J Cardiol. 2012;Epub ahead of print.