Key Points:
- Electrocardiography Defined: An ECG records the heart’s electrical activity in real time, offering a rapid window into rate, rhythm and conduction. The ECG measures changes in voltage between different body leads, displayed on grid paper where the horizontal axis = time and the vertical axis = voltage.
- Mastering the basic components (waves, intervals, conduction), is importantl before tackling advanced interpretation.
- Why it matters: Mastery of these elements underpins accurate diagnosis and timely management of everything from benign findings to rapidly fatal conditions.
Core Waveforms & Intervals
- P wave: atrial depolarization
- QRS complex: ventricular depolarization
- T wave: ventricular repolarization
- PR interval: atrial-to-ventricular conduction time
- QT interval: total ventricular depolarization + repolarization
Lead Placement
- Proper lead placement ensures accurate axis, morphology, and rhythm interpretation.
- Misplacement is a frequent cause of misdiagnosis.
Normal Cardiac Conduction
- SA node → atria → AV node → His-Purkinje system → ventricles.
- Knowing this sequence helps identify where conduction is blocked or abnormal.
Common Variants & Early Pathology
- Axis determination distinguishes normal from right or left axis deviation, helping uncover conduction disease, ventricular strain, or acute pathology.
- Voltage assessment identifies high or low voltage patterns, which may point toward conditions such as pericardial effusion, COPD, or ventricular hypertrophy.
- A wide QRS complex demands consideration of bundle branch blocks, ventricular rhythms, and pre-excitation.
- Careful inspection of ST segments and T waves is essential for recognizing early ischemia, hyperkalemia, or benign repolarization variants.
KEY CLINICAL PEARLS:
- Systematic Approach: Always use a consistent, step-by-step approach to ECG interpretation to ensure that no important findings are overlooked.
- Correlate with Clinical Context: ECG findings should always be interpreted in light of the patient’s symptoms and clinical history for accurate diagnosis and treatment.
- Recognize Normal Variants: Familiarize yourself with normal variants to avoid over-diagnosing conditions based on benign ECG findings.
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