Coronary artery disease (CAD) is a form of atherosclerosis in which fatty plaque accumulates inside the coronary arteries and obstructs the supply of oxygenated blood to the heart. CAD typically develops slowly and asymptomatically over many years. (1) It is believed the damage or injury is to the coronary artery’s inner layer, endothelial cell layer. Once the artery has been injured, the accumulation of fatty deposits may increase the risk of CAD, along with the individual’s family history of heart disease. Some patients experience or develop symptoms, such as angina (chest pressure or tightness), shortness of breath, heart attack or myocardial infarction (MI), while others do not, known as asymptomatic. Some patients never experience overt CAD symptoms until they suffer a major cardiovascular event (MACE), such as a MI.
An ERCI 2012 review of CAD stated, “About 16.3 million U.S. adults (i.e., 20 years of age and older) are living with CAD and about 1.26 million cases of new (785,000) or recurrent (470,000) CAD are diagnosed annually. About 450,000 Americans die of CAD each year, of whom more than 80% are 65 years of age or older. The lifetime risk of developing CAD after 40 years of age is about 49% for men and 32% for women.” (1)
Endothelial function (EF) assessment or testing (also known as peripheral arterial tonometry [PAT]) has been explored as a diagnostic aid to identify endothelial dysfunction and potential risk of CAD. Endothelial dysfunction has been measured by the percentage of flow-mediated dilation (FMD %) index with a proposed correlation to atherosclerotic outcomes. The FMD is obtained by using a device to slow the blood flow of a feeding artery in the finger (similar to a blood pressure cuff on the upper arm). When the pressure is released, the blood surge causes an endothelial-dependent FMD response. The results are given in percentages, showing the post-occlusion to pre-occlusion ratio that is calculated by the device’s computer software. EF testing is not designed as a screening method in the general population, but a supplement to the physician’s decision-making process, along with the patient’s history and other clinical findings. (2)
The Endo PAT 2000™ (representing endothelial-peripheral arterial tonometry) device developed by Itamar Medical, Ltd, Israel, as a non-invasive diagnostic test for coronary artery endothelial dysfunction. The U.S. Food and Drug Administration (FDA) cleared the Endo PAT 2000 device on November 13, 2003 as a 510(k) that uses a reactive hyperemia (presence of blood flow to a body part or organ) procedure measuring the peripheral arterial tonometry or tone (PAT). This device is a next generation version of Itamar’s PAT 1000Rd ™ (representing peripheral artery tonometer) FDA cleared on February 21, 2001. (2)
The Endo PAT 2000 consists of a main control unit, finger probes and tubing and a software package. The Endo PAT 2000 main control unit is connected to two independent, thimble-shaped, finger mountable probes via two air-conducting tubes. A standard computer is connected to the Endo PAT 2000 main control unit for online display and archiving of device recordings and off-line analysis. The output of the Endo PAT 2000 probe are pressure fluctuations sensed at its distal compartment induced by the volume changes of the pulsating digital arteries. (3) Thus, assessing the endothelial dysfunction, positive or negative and providing an EndoScore (the FMD %) within 15 minutes, administered in the physician office or hospital. Low scores indicate the need for medical attention, where as a higher score may assist in making further medical assessment decisions by the physician. (3)