MTWA-CAD is a feasibility study designed to evaluate Microvolt T-Wave Alternans (MTWA) testing for the purpose of detecting active ischemia in patients with known or suspected coronary artery disease (CAD). MTWA is a subtle, alternating pattern in the T wave portion of the surface electrocardiogram (ECG) that is associated with increased risk of ventricular tachyarrhythmias and sudden cardiac arrest (SCA).

Ischemia, a common trigger for arrhythmias, is a well-documented cause of repolarization alternans. Human studies have shown that active ischemia can be associated with visible as well as microvolt-level T-wave alternans. While MTWA testing is traditionally used to evaluate arrhythmic risk, this known association with ischemia may allow MTWA testing to be used as a diagnostic tool to detect underlying CAD. The MTWA-CAD study will assess the feasibility of this concept by measuring MTWA during routine nuclear stress testing or stress echocardiography with treadmill exercise. This is a feasibility study designed to verify preliminary observations under controlled environments and to generate hypotheses, endpoints, and sample sizes for future investigations.

Inclusion Criteria:

• Age 18 or above, or of legal age to give informed consent specific to state and national law
• Willing and capable of providing informed consent
• Willing and capable of undergoing a SPECT MPI exercise test (or stress echo) at an approved clinical investigational center
• In normal sinus rhythm at the time of the exercise test
• A life expectancy of more than 6 months

Exclusion Criteria:

• In atrial fibrillation at the time of the exercise test
• Left bundle branch block (precludes ST segment measurement)
• Pacemaker-dependent
• Life expectancy of less than 6 months
• Pregnancy

Subjects with known or suspected CAD who are scheduled to undergo routine exercise MPI or stress echocardiography testing for the detection of active ischemia in a cardiology practice or hospital setting.