ECG Abnormalities Part 1

ECG Abnormalities Part 1

• Bundle Branch Block (BBB): The Purkinje system usually transmits the cardiac impulse to both ventricles almost simultaneously. This normally results in the ventricles' electrical potentials canceling each other out. If one major bundle branch is blocked, the impulse travels through the healthy ventricle before the blocked one, causing delays.
• Left Bundle Branch Block (LBBB): Cardiac depolarization through the right ventricle occurs significantly faster than in the left ventricle. Consequently, the left ventricle remains polarized for about 0.1 seconds after the right ventricle has finished depolarizing. This leads to left axis deviation and a substantially prolonged QRS complex due to slow depolarization in the affected side of the heart.
• Right Bundle Branch Block (RBBB): When the right bundle branch is blocked, the left ventricle depolarizes considerably faster than the right ventricle. This causes the left side of the ventricles to become more electronegative for approximately 0.1 seconds before the right side. This results in right axis deviation and a prolonged QRS complex due to slow conduction.

Decreased Voltage of ECG

• Myopathies: A common cause of decreased voltage in a QRS complex is old myocardial infarctions resulting in reduced muscle mass. This slow movement of depolarization through the ventricles and decreased depolarization of significant portions of the heart contribute to QRS prolongation and decreased voltage.
• Conditions Surrounding the Heart: Fluid buildup in the pericardium (pericardial effusion) and pleural effusion or pulmonary emphysema can decrease voltage in the ECG.

Current Injury (Myocardial Ischemia)

• The J Point: The J point marks when depolarization wave finishes its passage through the heart, at the end of the QRS complex. This point is crucial for analyzing the electrical axis of injury potentials related to currents. A horizontal line is drawn at the J point to determine zero reference potential.

T Wave Abnormalities

• Slow Conduction and T-Wave Characteristics: If ventricular depolarization conduction is notably slow, the resulting T wave's polarity is frequently the opposite of the QRS complex.

• T-Wave Inversion: In myocardial ischemia, the T wave can invert reflecting the delay in depolarization.

• Digitalis Toxicity and the T Wave: Digitalis, a drug that increases cardiac muscle contractility, can cause T wave inversion or biphasic T waves at high dosages. This is due to varied depolarization durations across different parts of the ventricles.