Understanding ECG: Components and Leads

• ECG, or electrocardiogram, is a non-invasive test recording the heart's electrical activity over time.
• Used to detect and diagnose heart conditions, including arrhythmias, heart attacks, and heart failure.
• The ECG machine uses electrodes attached to the chest, arms, and legs to detect the heart’s electrical signals.
• These signals are transmitted to the ECG machine, which records them on a graph.

Basic ECG Components

• The ECG tracing includes distinct waveforms: P wave, QRS complex, and T wave.
• The P wave indicates atrial depolarization, which leads to atrial contraction.
• The QRS complex represents ventricular depolarization, resulting in ventricular contraction.
• The T wave represents ventricular repolarization as the ventricles relax for the next contraction.
• The U wave may sometimes appear and can indicate underlying conditions.

ECG Leads

• ECG leads offer different perspectives for recording the heart's electrical activity.
• A standard 12-lead ECG uses 10 electrodes to create 12 leads:
• Three standard limb leads: I, II, and III.
• Three augmented limb leads: aVR, aVL, and aVF.
• Six precordial (chest) leads: V1, V2, V3, V4, V5, and V6.
• Each lead offers a unique view of the heart's electrical activity, enabling assessment of different heart areas.

ECG Paper and Measurements

• ECG paper records the ECG tracing using graph paper.
• Each small square represents 0.04 seconds horizontally and 0.1 millivolts (mV) vertically.
• Each large square (5 small squares) represents 0.20 seconds horizontally.
• Measurements of waveform duration and amplitude enable assessment of the heart's electrical activity for abnormalities.

Heart Rate Determination

• Heart rate can be determined by measuring the distance between consecutive R waves (R-R interval) on the ECG.
• For a regular rhythm, divide 300 by the number of large squares between two consecutive R waves to calculate heart rate.
• For irregular rhythms, estimate heart rate by counting R waves in a 6-second strip (30 large squares) and multiplying by 10.

Rhythm Analysis

• Rhythm analysis assesses the regularity and rate of the heart's electrical activity.
• Normal sinus rhythm (NSR) includes a regular heart rate (60-100 bpm) with a P wave before each QRS complex.
• Arrhythmias, or abnormalities in the heart's rhythm, can be detected via ECG.
• Common arrhythmias include:
• Sinus bradycardia (slow heart rate).
• Sinus tachycardia (fast heart rate).
• Atrial fibrillation (irregular and rapid atrial activity).
• Ventricular tachycardia (fast, life-threatening ventricular activity).
• Heart blocks (disruptions in the electrical conduction pathway).

Waveform Morphology

• Waveform morphology describes the shape, size, and characteristics of ECG waveforms.
• Abnormal waveform morphology can indicate underlying heart conditions.
• Examples:
• Tall, peaked T waves may indicate hyperkalemia.
• Inverted T waves may suggest myocardial ischemia.
• ST segment elevation may indicate myocardial infarction.
• Prolonged QRS duration may indicate a bundle branch block.

Intervals and Segments

• ECG intervals and segments provide info on the timing/duration of electrical events in the heart.
• The PR interval is the time for the electrical impulse to travel from atria to ventricles.
• The QRS duration represents the time it takes for the ventricles to depolarize.
• The QT interval represents the time it takes for the ventricles to depolarize and repolarize.
• The ST segment is the period between ventricular depolarization and repolarization.
• Abnormalities in intervals and segments can indicate heart conditions and conduction abnormalities.