Test to Predict Who May Benefit from Implanted Defibrillators

A test that measures tiny changes in the electrical activity of the heart may identify which patients with heart disease are at negligible risk of sudden cardiac death due to ventricular arrhythmia and therefore may not benefit from an implantable cardioverter defibrillator (ICD). The ICD is a device that terminates arrhythmias with a high-energy shock.

HearTwave® II Microvolt T-Wave Alternans System.

Photo courtesy of Cambridge Heart.

The microvolt T-wave alternans (MTWA) test detects minute fluctuations in the portion of the electrocardiogram (ECG) known as the T-wave. This electrical instability may precede ventricular tachyarrhythmia in patients with chronic heart disease.

How the Test Works

High-resolution electrodes are placed on the patient’s chest before controlled exercise. Voltage changes are measured and the results are interpreted by a cardiologist.

The HearTwave® II System (Cambridge Heart, Bedford, MA) is a commercial MTWA test that uses spectral analysis. Another MTWA system, the Marquette
(GE Healthcare) uses an algorithm, but not spectral analysis, to detect fluctuations in the T-wave.

Regulatory Status

The HearTwave® II System received approval from the US Food and Drug Administration (FDA) in April 2005 for use as an adjunct therapy to clinical history and other diagnostic tests. A licensing application for the HeartTwave® II System was submitted to Health Canada in March 2006.

Selecting Patients for ICDs

ICDs effectively prevent death from ventricular arrhythmias in patients with impaired left ventricular ejection fraction.[1]

Using MTWA testing as a risk stratification tool could potentially identify which heart patients are at a negligible risk of sudden death and could therefore avoid costly ICD therapy and its attendant risks.[2] Other than measuring left ventricular ejection fraction (commonly measured by echocardiography), there are no alternative non-invasive tests.[3]

Evidence

A meta-analysis evaluating the predictive value of MTWA testing in 2,608 patients with various types of heart disease found that 97.2% of those with a negative MTWA test had no ventricular arrhythmias during an average follow-up of 21 months. However, of the patients who had a positive MTWA test, ventricular arrhythmias occurred in only 19.3%.[4]

A multicentre US study found that among patients with heart disease and a left ventricular ejection fraction of less than 40%, MTWA testing could identify patients at high risk for sudden cardiac death, and patients at low risk who are unlikely to benefit from ICDs.[1]

Cost

The HearTwave II System costs US$29,900. Each set of single-use Micro-V Alternans™ sensors costs approximately US$75.

US Policy Decisions

Blue Cross Blue Shield recently concluded that there was insufficient evidence to reimburse for MTWA testing.[3] However, in March 2006, the US Centers for Medicare and Medicaid Services decided to reimburse for MTWA testing because of the higher risk of sudden cardiac death due to ventricular arrhythmia and an increased likelihood of potential harms caused by ICD placement in the older Medicare population.[2]

References

[1] Bloomfield DM, et al. J Am Coll Cardiol 2006;47(2):456-63.

[2] Decision memo for Microvolt T-wave Alternans (CAG-00293N). In: Medicare coverage database. Washington: U.S. Dept. of Health and Human Services; 2006. Available: https://www.cms.hhs.gov/mcd/viewdecisionmemo.asp?id=165.

[3] Microvolt T-wave alternans testing to risk stratify patients being considered for ICD therapy for primary prevention of sudden death. [TEC assessment vol 20, no 9]. Washington: Blue Cross Blue Shield Association; 2005. Available: http://www.bcbs.com/tec/Vol20/20_09.pdf.

[4] Gehi AK, et al. J Am Coll Cardiol 2005;46(1):75-82