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Pseudo-ST-depression, which is a wandering baseline due to poor skin contact of the electrode [3] Physiologic J-junctional depression with sinus tachycardia [3] Hyperventilation [3] Horizontal ST depression in V4, V5, V6 leads during a cardiac stress ECG. Other, non-ischemic, causes include: Side effect of digoxin [4] [3] Hypokalemia [4] [3]
Schematic representation of normal ECG. In electrocardiography, the ST segment connects the QRS complex and the T wave and has a duration of 0.005 to 0.150 sec (5 to 150 ms). It starts at the J point (junction between the QRS complex and ST segment) and ends at the beginning of the T wave.
An ST elevation is considered significant if the vertical distance inside the ECG trace and the baseline at a point 0.04 seconds after the J-point is at least 0.1 mV (usually representing 1 mm or 1 small square) in a limb lead or 0.2 mV (2 mm or 2 small squares) in a precordial lead. [2]
proportionally excessively discordant ST elevation in V1-V4, as defined by an ST/S ratio of equal to or more than 0.20 and at least 2 mm of STE. (this replaces Sgarbossa criterion 3 which uses an absolute of 5mm) Wackers et al. correlated ECG changes in LBBB with localization of the infarct by thallium scintigraphy. [7]
Diagnosis is based on an ECG showing ST-segment depression at the J-point of 1 to 3 mm in leads V1 to V6, with tall and symmetrical T waves. [1] The ST-segment is upsloping and there is also often ST-segment elevation of 0.5 to 2 mm in lead aVR. [1] [2] The QRS complex is either normal or slightly wide. [1]
ECG would be abnormal in 75 to 95% of the patients. Characteristic ECG changes would be large QRS complex associated with giant T wave inversion [4] in lateral leads I, aVL, V5, and V6, together with ST segment depression in left ventricular thickening. For right ventricular thickening, T waves are inverted from V2 to V3 leads.
Benign early repolarization (BER) or early repolarization is found on an electrocardiogram (ECG) in about 1% of those with chest pain. [2] It is diagnosed based on an elevated J-point / ST elevation with an end-QRS notch or end-QRS slur and where the ST segment concave up. It is believed to be a normal variant.
Bifascicular block is a combination of right bundle branch block and either left anterior fascicular block or left posterior fascicular block. Conduction to the ventricle would therefore be via the remaining fascicle. The ECG will show typical features of RBBB plus either left or right axis deviation. [7] [8]