ST-segment depression

ECG: Signs of left ventricular hypertrophy with positive Sokolow criterion (40), slightly widened QRS (100 ms), delayed intrinsicoid deflection in V4, V6; ST segment depression in leads I, aVL, V4, V5, V6 with negative T-waves;

ECG 2: 65-year-old man, non-insulin-dependent diabetic, hypertensive, hospitalized for chest pain of increasing intensity, initially occurring on exertion and thereafter at rest since 2 days; increased troponin;

ECG 2: This per-critical electrocardiogram shows a sinus rhythm of 95 bpm, with a ST segment elevation of 3 mm in aVR, of 2 mm in V1 and a widespread and relatively prominent ST segment depression (inferior leads, V3-V6);

Comments: The normality criterium for ST segment depression is that the ST segment must not deviate more than 0.5 to 1 mm below the isoelectric line. As in the case of ST elevation, this electrocardiographic sign taken individually is poorly specific; in order to facilitate diagnosis, it is also important to know the clinical context (thoracic pain, neurological disease, etc.), to specify the characteristics of the depression (localized or widespread), ascending or descending, coved pattern, territory and leads involved, etc.) and to search for associated electrical signs (elevation and Pardee wave, conduction disorder, necrosis q wave, SIQ3 pattern, left ventricular hypertrophy, QT-interval, etc). It may also be important to repeat the recording of the tracings to establish its stable or evolving nature. Different diseases and clinical situations can be associated with a ST segment depression:

• Reciprocal depression: a ST segment depression in the leads opposite those that directly explore the ischemic territory is common but inconsistent depending on the localization of the occlusion; this indirect reciprocal sign has a high diagnostic value even if of limited amplitude;
• Depression and non-ST elevation myocardial infarction (NSTEMI): the electrical sign characteristic of NSTEMI or of unstable angina is the presence of ST segment depression which can be transient and dynamic; the amplitude of the ST segment depression may be of variable (at least > 0.05 mV), rectilinear, horizontal or descending amplitude in at least 2 contiguous leads corresponding to a defined territory; the greater the amplitude of the depression, the greater likelihood of an acute coronary origin (an elevation ≥ 2 mm in several leads is highly evocative); the presence of a diffuse depression associated with an elevation in aVR should evoke the presence of a lesion of the left coronary artery trunk;
• Left bundle branch block: there is generally an appropriate discordance between the ST segment and the T-wave in the precordial leads (elevation and positive T-wave if QRS is negative, depression and negative T-wave if QRS is positive); a depression in the left precordial leads (V5, V6) is therefore frequent; failure to observe the appropriate discordance should evoke the presence of a myocardial infarction in the setting of typical chest pain;
• Left ventricular hypertrophy: it is also common to find an appropriate discordance with depression in the left precordial leads;
• Right ventricular pacing: in right ventricle-paced patients, the electrical pattern may be similar to that observed in a left bundle branch block with possible evidence of a depression in the left precordial leads;
• Pericarditis and pericardial effusion: a moderate and widespread depression associated with a low-voltage pattern should evoke the diagnosis;
• Digoxin treatment: a downward coved pattern reflects the presence of a digitalis impregnation (pattern resembling Dali’s mustaches);
• Others: hypokalemia (diffuse depression, inverted or flattened T-waves, prolongation of the QT-interval), right ventricular hypertrophy (depression in right leads), right bundle branch block (depression in right precordial leads), supraventricular tachycardia (frequent depression in left precordial leads);

Take-home message: In the presence of chest pain and ST segment depression, certain signs are suggestive of an ischemic origin: rectilinear, horizontal or descending depression in at least 2 contiguous leads corresponding to a defined territory; the greater the amplitude of the depression, the greater likelihood of an acute coronary origin (a depression ≥ 2 mm in several leads is highly evocative).