NSTEMI and unstable angina

ECG 2A: Sinus rhythm, normal PR interval; significant depression in leads V1 to V4 with negative T-waves;

ECG 2B: ECG recorded after a coronary angiography with evidence of proximal LAD sub-occlusion and treatment with angioplasty and stent placement; moderate increase in cardiac enzymes leading to the diagnosis of NSTEMI; normalization of the ST-segment and T-wave polarity;

Patient: 65-year-old man, COPD with chronic respiratory failure, hospitalized for chest pain initially occurring during exercise and then at rest; ECG recorded during an episode of pain;

ECG 2C: sinus rhythm, right bundle branch block pattern with left anterior fascicular block (left axis); ST-segment depression from V2 to V5;

ECG 2D: ECG recorded after administration of 2 puffs of nitroglycerine; regression of the amplitude of the depression; the biological work-up did not show increase in cardiac enzymes leading to a diagnosis of unstable angina; coronary angiography showed a very severe stenosis of the LAD;

Comments: These two patients presented an acute coronary syndrome with evidence of ST-segment depression. An acute coronary syndrome occurs when an atheromatous plaque becomes unstable leading to total or partial occlusion of a coronary artery. Acute coronary syndromes can be divided into unstable angina, NSTEMI (non-ST-segment elevation myocardial infarction), and STEMI (ST-segment elevation myocardial infarction). The differentiation between NSTEMI and unstable angina is based on the measurement of cardiac enzymes, their electrocardiographic pattern being similar. Indeed, in a NSTEMI, the elevation in enzymes is indicative of myocardial necrosis whereas in unstable angina there is no significant increase.

The characteristic electrical sign of NSTEMI or unstable angina is the presence of a ST-segment depression which may be transient and dynamic; the electrocardiogram can be normal outside of pain, it is thus important to repeat ECG registrations. ST-segment depression may be of variable amplitude (at least > 0.05 mV), rectilinear, horizontal or descending, in at least 2 contiguous leads corresponding to a defined territory. The greater the amplitude of the depression, the greater the likelihood of an acute coronary origin (an elevation ≥ 2 mm in several leads is highly evocative). The T-waves can be reversed, symmetrical and more or less deep. By definition, there is no ST-segment elevation in a NSTEMI.

Take-home message: In an unstable angina or a NSTEMI, the electrocardiogram can reveal a ST-segment depression with negative waves.