Myocardial Repolarization Disorders

Role of ECG in diagnosing repolarization abnormalities

Electrocardiography is the primary tool for screening the condition of the heart muscle. Regular ECG recordings, which should be performed at least once a year (or more often if clinically indicated), allow for the timely detection of various pathological patterns.

The main objective of this study is to identify signs of ischemic myocardial damage, left ventricular hypertrophy, as well as rhythm and conduction disturbances, and directly, repolarization abnormalities. It is important to note that the electrocardiographic picture allows tracking disease progression and adjusting prescribed therapy.

Impact of metabolic shifts and electrolytes

Specific changes on the cardiogram are often not directly related to ischemia, but they are critically important for differential diagnosis. First of all, this concerns fluctuations in blood electrolyte levels:

• Hyperkalemia leads to a pronounced transformation of the T wave. It becomes excessively tall, acquires a symmetrical, "peaked" shape with a narrow base.
• Hypokalemia causes characteristic repolarization abnormalities: ST-segment depression, T-wave flattening, and the appearance of a prominent U wave are observed.
• Hypercalcemia affects the temporal parameters of the cardiac cycle, manifesting as a shortening of the Q-T interval.

Drug-induced and cerebrogenic factors

Certain pharmacological agents have a direct impact on the electrical activity of the heart. A prime example is cardiac glycosides. Their intake is characterized by a specific form of ST-segment displacement—the so-called "scoop-like" depression. In addition, the T-wave amplitude decreases and the Q-T interval shortens. Prolonged use of these drugs has an arrhythmogenic effect, provoking ventricular extrasystoles, non-paroxysmal AV nodal tachycardia, ventricular tachycardia, and various blocks.

Particular attention should be paid to cerebrogenic changes. In acute central nervous system pathologies, such as stroke or hemorrhage, pronounced repolarization abnormalities can occur. They are capable of completely mimicking primary cardiac pathology, requiring careful differential diagnosis.

Repolarization shifts in chronic carditis

Chronic carditis is often asymptomatic and diagnosed only at the stage of decompensation. Depending on the morphology, congestive, hypertrophic, and restrictive variants are distinguished, each with its own ECG features.

In the congestive variant, where cardiosclerosis and left ventricular dilatation with reduced contractility predominate, persistent repolarization abnormalities and Q-T interval prolongation are recorded on the ECG. Additionally, there is a decrease in QRS voltage, signs of left heart overload, and pronounced arrhythmias (including atrial fibrillation and extrasystoles).

In the hypertrophic variant, accompanied by pulmonary hypertension and right ventricular failure, the cardiogram reveals signs of subendocardial hypoxia and myocardial ischemia, as well as persistent conduction disturbances of various localizations. At the same time, other rhythm disturbances, except for characteristic bradycardia, are atypical for this form.

Manifestations of myocarditis in children

The diagnosis of myocardial damage in childhood relies on a comprehensive approach, where ECG remains the primary screening tool. Repolarization phase abnormalities in this case manifest as ST-segment displacement, as well as T-wave flattening or inversion (formation of a negative wave).

If myocarditis has a toxic etiology, ST-T complex changes are accompanied by PR interval prolongation and various blocks. In infectious lesions, non-specific ST-segment and T-wave changes, sinus tachycardia, and signs of myocardial hypoxia are more common. It is important to remember age-related norms: isolated incomplete right bundle branch block and sinus arrhythmia in children can be a variant of normal and should not be mistakenly interpreted as signs of inflammation.

Class and exam questions

What else to study on this topic

• Clinical and anatomical variants of chronic carditis
• Signs of pulmonary hypertension in hypertrophic carditis
• Specific markers of cardiomyocyte damage (troponins, AST)
• Instrumental diagnostics of myocarditis: capabilities of EchoCG and MRI
• Indications for right ventricular myocardial biopsy

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.