Friday, 11 December 2009

The 80 lead ECG

ST elevation myocardial infarction (STEMI) is the most serious form of heart attack. The ST segments elevate because the full thickness of heart muscle is injured (transmural injury). This full thickness injury and ST elevation is the result of a total occlusion of a coronary artery. Some STEMIs, particularly those involving the posterior or back surface of the heart, may be missed by the present traditional system of placing a limited number of leads on the front of the chest.
In contrast to the 12 leads of data and the limited anterior or front view of the heart from a traditional ECG, an 80 lead ECG (such as the PRIME ECG®) utilizes 80 leads placed on both the front and back of the patient to analyze a 360-degree spatial view of the heart. This new technology may allow the more rapid and accurate detection of STEMI and thereby potentially speed the delivery of care.

Analysis is performed on a computer selected representative beat. ST-segment elevation and depression are translated into colors (red = elevation, blue = depression) and displayed against a 3 dimensional torso image for physician review. These images allow for rapid pattern recognition that identifies problem areas that correlate with regions of ischemia or infarction. This use of graphic imaging allows the physician to quickly focus on specific ECG morphology that contains the most valuable diagnostic information without having to expend time exploring data from all 80 leads. System software facilitates examination of the actual ECG trace for each of the 80 recordings. The user places a cursor over the suspect area and a pop-up window reveals the underlying electrode tracing and provides the value of elevation or depression at that lead. Ten years of clinical data and in-hospital experience have demonstrated an increase in sensitivity over the 12 lead ECG in the range of 18% with no loss in specificity. As a result, there is the potential to detect up to 40% more ST Elevation MIs (serious heart attacks) than the traditional 12-lead ECG.

Registry data from the National Registry of Myocardial Infarction (NRMI), CRUSADE and GRACE have demonstrated that there are significant opportunities for improvement in door-to-balloon time and door-to-needle time in the management of serious heart attacks (STEMI). The 80 lead ECG may provide a technological advance that would speed the correct diagnosis of ST elevation MI. A substantial number of patients have a non-diagnostic 12-lead and these patient may wait for extended periods in the emergency room pending the results of enzymes released into the bloodstream (biomarkers) to diagnose a heart attack.

Heart attacks involving the back side of the heart may cause ST depression rather than ST elevation (STEMI) becuase the pattern of electrical injury is reversed on the traditional 12 lead ECG. One of These patients may currently be receiving less aggressive care because of a diagnosis of non-ST-elevation MI (NSTEMI) based on ST-depression, which may in fact be ST-elevation in a portion of the heart not visible with the 12 lead. Assuming approximately 20-30% of diagnosed MI patients are now diagnosed as STEMI patients and 70-80% are diagnosed as NSTEMI, the PRIME data would indicate that approximately 1 in every 3 patients may be in fact a higher risk category and be suitable for more aggressive care.

A nurse places an 80 lead EGG on a patient

Shown to the right is the 12 lead ECG in a patient that presented with substernal chest pain. Note that there are non diagnostic changes. There is no evidence of ST segment elevation.

An 80 lead ECG vest was then placed. Shown to the right are the 80 EKG lead tracings displayed individually. The anterior leads are displayed on the left had side. The posterior or back of the heart leads are displayed on the right hand side of the figure. For instance lead 68 shows ST elevation. Posterior and right-sided leads reveal ST-elevation, where the 12-lead was silent.

In order to display the data in a more clinically relevant and intuitive fashion, the area of injury is shown in red on the patient's back, corresponding to the inferior-posterior location of the MI.