1. General Introduction to ST, T, and U wave abnormalities
Basic Concept: the specificity of ST-T and U wave abnormalities is provided more by the clinical circumstances in which the ECG changes are found than by the particular changes themselves. Thus the term, nonspecific ST-T wave abnormalities, is frequently used when the clinical data are not available to correlate with the ECG findings. This does not mean that the ECG changes are unimportant! It is the responsibility of the clinician providing care for the patient to ascertain the importance of the ECG findings.
Factors affecting the ST-T and U wave configuration include:
Atrial repolarization (e.g., at fast heart rates the atrial T wave may pull down the beginning of the ST segment)
Ventricular conduction abnormalities and rhythms originating in the ventricles
"Secondary" ST-T Wave changes (these are normal ST-T wave changes solely due to alterations in the sequence of ventricular activation)
ST-T changes seen in bundle branch blocks (generally the ST-T polarity is opposite to the major or terminal deflection of the QRS)
ST-T changes seen in fascicular block
ST-T changes seen in nonspecific IVCD
ST-T changes seen in WPW preexcitation
ST-T changes in PVCs, ventricular arrhythmias, and ventricular paced beats
"Primary" ST-T Wave Abnormalities (ST-T wave changes that are independent of changes in ventricular activation and that may be the result of global or segmental pathologic processes that affect ventricular repolarization)
Drug effects (e.g., digoxin, quinidine, etc)
Electrolyte abnormalities (e.g., hypokalemia)
Ischemia, infarction, inflammation, etc
Neurogenic effects (e.g., subarrachnoid hemorrhage causing long QT)
2. Differential Diagnosis of ST Segment Elevation
Normal Variant "Early Repolarization" (usually concave upwards, ending with symmetrical, large, upright T waves)
Example #1: "Early Repolarization": note high take off of the ST segment in leads V4-6; the ST elevation in V2-3 is generally seen in most normal ECG's; the ST elevation in V2-6 is concave upwards, another characteristic of this normal variant.
Basic Concept: the specificity of ST-T and U wave abnormalities is provided more by the clinical circumstances in which the ECG changes are found than by the particular changes themselves. Thus the term, nonspecific ST-T wave abnormalities, is frequently used when the clinical data are not available to correlate with the ECG findings. This does not mean that the ECG changes are unimportant! It is the responsibility of the clinician providing care for the patient to ascertain the importance of the ECG findings.
Intrinsic myocardial disease (e.g., myocarditis, ischemia, infarction, infiltrative or myopathic processes)
ST segment depression is often characterized as "horizontal", "upsloping", or "downsloping"
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