Characteristics of Ischemic ST Depression

The ST-segment depression seen with nontransmural ischemia typically is either horizontal (flat) or downsloping, and the ST segment is usually quite straight, as shown in Figure 10.2. Also note that the ST segment in ischemia typically intersects with the T wave at a fairly abrupt angle. Both the straight ST segment and the abrupt transition into the T wave are in contrast to other causes of ST depression. Left ventricular hypertrophy, for example, has downsloping ST depression, but it is typically upwardly convex, and there is a gentle transition into the T wave (Figure 10.3).

Figure 10.2. Ischemia. Horizontal ST-segment depression associated with ischemia. Note that the ST segment is quite straight and intersects with the T wave at a fairly sharp angle,

Characteristics of Ischemic ST Depression 87

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Figure 10.3. Left ventricular hypertrophy. Note that the ST depression in LVH is downsloping, as ischemia can be, but that the ST segment is convex as opposed to straight, and gently blends into the T wave.

Figure 10.3. Left ventricular hypertrophy. Note that the ST depression in LVH is downsloping, as ischemia can be, but that the ST segment is convex as opposed to straight, and gently blends into the T wave.

Upsloping ST depression, on the other hand, much less often represents ischemia and, in fact, is quite normal during periods of exercise or other causes of tachycardia. This normal exertional ST depression is often referred to as J point depression (Figure 10.4).

ST depression is measured from the isoelectric line, usually established by the PR segment. As a general rule, the deeper the ST depression, the more

Figure 10.4. J point depression. Upsloping ST depression from the J point, which is a physiologic response to exercise or tachycardia.

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Figure 10.5. Ischemia. ECG of a 76-year-old white male recorded during an episode of angina. Note up to 3 mm of horizontal or downsloping ST depression in the anterolateral wall. In addition, pathologic Q waves are present in leads III and aVF, reflecting a previous inferior wall infarction.

Figure 10.5. Ischemia. ECG of a 76-year-old white male recorded during an episode of angina. Note up to 3 mm of horizontal or downsloping ST depression in the anterolateral wall. In addition, pathologic Q waves are present in leads III and aVF, reflecting a previous inferior wall infarction.

severe the ischemia. In addition, the deeper the ST depression, the greater the specificity for ischemia. ST depression of <1 mm is an unreliable indicator of ischemia. Figure 10.5 shows the full 12-lead ECG of a patient with severe ischemia during an anginal attack.

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