Myocardial repolarization on the ECG

Main ECG signs of repolarization disorders

On an electrocardiogram, the processes of ventricular electrical potential recovery can be impaired in various pathological conditions. Instrumentally, such deviations are recorded as the following changes:

• ST segment displacement (deviation from the baseline).
• Flattening of the T wave.
• T wave inversion (formation of a pronounced negative wave).

Such electrocardiographic anomalies and specific repolarization abnormalities serve as a crucial diagnostic marker. For instance, they were included in the historical 1994 diagnostic criteria for identifying dangerous pathologies of the heart muscle.

Secondary abnormalities in bundle branch blocks

The diagnosis of bundle branch block (BBB) is established solely based on electrocardiography data. In addition to the deformation and pathological widening of the ventricular QRS complex up to 0.12–0.20 seconds, this condition is characterized by so-called secondary repolarization abnormalities.

They manifest as the phenomenon of discordance—the opposite direction of the main wave of the deformed QRS complex and the T wave. This means that if the dominant QRS wave is directed upward, the T wave will be negative (directed downward), and vice versa. It is worth noting that ventricular tachycardia with left bundle branch block (LBBB) morphology often accompanies severe structural lesions of the right heart chambers.

Monitoring of the QT interval and early repolarization

Assessment of the repolarization phase is strictly mandatory when prescribing drug therapy to patients with inflammatory diseases, specifically all hospitalized patients with community-acquired pneumonia. The ECG analysis checklist includes:

1. Assessment of the duration of the QT interval.
2. Detection of signs of early repolarization syndrome.

This monitoring is necessary to ensure the safety of antibacterial therapy. A number of systemic antibiotics possess potential cardiotoxicity, the risk of which increases significantly in the presence of these ECG phenomena. Furthermore, electrocardiography in such patients helps rule out occult cardiac complications and identify concomitant diseases (including the risk of acute coronary syndrome or arrhythmias against the background of acute infection).

The role of repolarization in diagnosing ARVC

Repolarization abnormalities play a significant role in detecting arrhythmogenic right ventricular cardiomyopathy (ARVC). This is a relatively rare familial disease inherited predominantly in an autosomal dominant manner. It is based on mutations in desmosomal proteins, leading to histopathological replacement of the normal right ventricular myocardium with fibrous and adipose tissue. The process is predominantly localized in the "triangle of dysplasia" (outflow and inflow tracts, as well as the apex of the right ventricle).

The disease is accompanied by specific electrocardiographic anomalies. In the 1994 diagnostic criteria, ECG changes and repolarization abnormalities, along with a burdened family history and frequent ventricular extrasystoles (>1000 per 24 hours), were considered baseline signs. Early identification of these changes on the cardiogram is critically important, as right ventricular dysfunction is a frequent cause of sudden cardiac death in young people due to the development of severe life-threatening ventricular arrhythmias.

In diffuse involvement and chamber enlargement, echocardiography (EchoCG) findings often resemble dilated cardiomyopathy. Today, cardiac MRI is actively used for detailed evaluation of ventricular function.

Class and exam questions

What else to study on this topic

• Diagnostic criteria for ARVC (1994 and 2010): a combination of major and minor criteria.
• The role of MRI in assessing global and regional right ventricular systolic function.
• Late gadolinium enhancement and parametric mapping on MRI: capabilities and limitations with a thin RV wall.
• Computed tomography (CT) of the heart: detection of foci of myocardial replacement by adipose tissue.
• Classification of secondary cardiomyopathies (infiltrative, toxic, endocrine, nutritional, etc.).

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