Continuous 12lead

A typical instrument for continuous ST-segment monitoring is microprocessor-controlled and fully programmable (39). It can continuously acquire a new 12-lead ECG every 20 s and analyzes the ST-segments. The initial ECG is defined as the pretrigger ECG. If ST-segment elevation or depression occurs 0.2 mV in a single lead or 0.1 mV in two leads as compared with the pretrigger ECG, the device enters a potential alarm state. If four sequential ECGs have met the threshold criteria, then an alarm sounds and a 12-lead ECG is printed for physician review. This ECG then becomes the new pretrigger ECG for future ST-segment comparisons. Typically, a 12-lead ECG is saved every 20 min as well as any alarm ECGs. One can also print two-dimensional graphs of ST-segment trends (magnitude vs time) for the 12 individual leads or the average ST-segment magnitudes for the four regional groupings: anterior (Vj-V3), inferior (II, III, AVF), low lateral (V4-V6), and high lateral (I, AVL).

The practice of monitoring dysrhythmias in suspected cardiac patients became the standard of care when electrical and chemical defibrillation demonstrated the potential to terminate dysrhythmias. Similarly, with the advent of specific proven modalities to treat both AMI (with thrombolytics or angioplasty) and myocardial ischemia (with anticoagulants, vasodilators, circulation support devices, and angioplasty), there are sound reasons to evaluate and test the continuous 12-lead ECG.

There are two questions that continuous electrocardiography could address: first, it could aid in the early detection of potential candidates for thrombolysis or angioplasty while undergoing monitoring in the ED. This may occur in patients with suspected AMI whose initial ECG is nonspecific, but whose second ECG has at least 0.1 mV of ST-segment elevation in two contiguous leads. Second, in subgroups of ED patients, it could improve the diagnosis of ACI by detecting ST-segment changes that confirm the diagnosis of unstable angina or non-Q wave AMI. Since approx 50% of the patients with chest pain and AMI present to the ED without ST-segment elevation, and nearly 20% of these patients develop in-hospital electrocardiographic evidence of transmural infarction, continuous serial ECGs with ST-segment trend monitoring may identify the patient population most likely to benefit from rapid interventions following detection of electrocardiographic criteria diagnostic for AMI (40).

Table 3 Continuous 12-Lead ECG

ED diagnostic performance

ED clinical impact

Quality Accuracy

Quality

evidence (max = + + +)

of evidence Impact

B +

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