Practice Guidelines for Unstable Angina
Practice guidelines continue to proliferate, and their impact on clinical medicine remains to be fully elucidated. One of the most prolific sources of guidelines on a national basis is the Agency for Health Care Policy and Research (AHCPR), which has issued guidelines on unstable angina (1994). A goal of the guidelines was to define the methods of diagnosis and treatment that would result in the greatest benefit. This study examined the applicability of the AHCPR guidelines in the emergency department setting, as well as the potential impact on hospital admission.
Consecutive patients (n = 457) with a provisional diagnosis of unstable angina as ascertained by emergency physicians were evaluated. Discrepancy between the actual ED disposition and the guideline recommendations were found primarily in the "low-risk" group, where only one of 28 patients was actually sent home and the "high-risk" group, where only 72 of 182 were admitted to an ICU.
Since the size of the "low-risk" group is so small (6%), the intention to reduce hospitalizations by identifying individuals safe for discharge home is unlikely to have a major effect. At the same time, the substantial size of the "high-risk" group not admitted to ICU beds might suggest that full adherence to the guidelines would actually increase expenditures when compared to the use of less expensive telemetry bed disposition. The authors conclude with a statement that empiric data from clinical settings to determine actual guideline impact are desirable, prior to widespread promulgation.
Katz D, et al. JAMA 1996;276: 1568-1574.
Clinical Scenario: The ECG in the figure was obtained from a 67-year-old woman who presented to the office with a history of recent chest pain. How would you interpret her tracing?
Interpretation: The rhythm is sinus at a rate of 70 beats/min. The mean QRS axis is +50°, and all intervals are normal. There is no evidence of chamber enlargement.
The most remarkable finding on this tracing is the appearance of the ST segments in the inferior and lateral precordial leads. Although the up-ward concavity of the ST segments in these leads may at first glance suggest the presence of early repolarization, the peak of the T waves is broader and appears more prominent than is usually seen with early repolarization. Moreover, the normal variant pattern of early repolarization is much less common in older individuals. Especially in the presence of chest pain, the diagnosis of early repolarization should always be one of exclusion, made only after comparison with previous tracings that repeatedly show a pattern of similar ST segment elevation during asymptomatic periods.
In this particular tracing, the appearance of the ST segment in leads aVL, V2, and V3 should suggest that something is amiss. ST segment depression and T wave inversion in these leads is abnormal and consistent with reciprocal changes that should serve to increase suspicion of acute infarction.
Clinically, the 67-year-old woman in this case had a cardiac arrest five minutes after this ECG was recorded. She was successfully resuscitated, but still went on to evolve an acute inferolateral infarction. In retrospect, the ST segment elevation in the figure shown therefore represented a hyperacute T wave change. Hyperacute T waves often mark the earliest phase of acute infarction. This stage of evolution tends to be short-lived, and is easy to overlook because ST-T wave changes may be quite subtle. Often, the T wave simply looks "funny"being broader and more peaked than expected, as if trying to raise the T segment without yet doing so. As a result, it will sometimes be admittedly difficult to distinguish the hyperacute T wave phase of acute infarction from the ST segment elevation of early repolarization. Clues for facilitating this distinction may be forthcoming from attention to the clinical history, comparison with previous tracings on the patient (if available), and recognition of reciprocal ST-T wave changes (that should not be present with early repolarization).
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