Key Points
- ECGs capture cardiac waveforms from changes in voltage measured between different points on the body.
- Each waveform recorded represents a specific portion of the electrophysiological events that occur during each cardiac cycle.
- Waveforms are described based on amplitude, duration and morphology.
- Segments are lines that connect waveforms.
- Intervals are durations of time that include waveforms and segments.
Waveforms: The Heart's Electrical Signature
- Waveforms on an ECG reflect distinct phases of the heart’s electrical activity. Each waveform corresponds to a specific event in the cardiac cycle—such as atrial depolarization (P wave), ventricular depolarization (QRS complex), and ventricular repolarization (T wave).
- Waveforms are characterized by three key features:
- Amplitude: The height or depth of the waveform, indicating the magnitude of voltage change.
- Duration: The length of time the waveform persists, measured in milliseconds (ms), reflecting the speed of the electrical event.
- Morphology: The shape of the waveform, which can provide insights into the direction, speed, and origin of the electrical impulse
Waveforms to Know:
Segments: Connecting the waveforms
- Segments are the straight lines on the ECG that connect two waveforms. They represent periods when the heart's electrical activity is relatively stable, with no significant changes in voltage.
- Example: The ST segment connects the end of the QRS complex (ventricular depolarization) to the beginning of the T wave (ventricular repolarization). It’s crucial in diagnosing conditions like myocardial ischemia.
Segments to Know:
Intervals: Timing the Cardiac Cycle
- Intervals encompass both waveforms and segments, representing the duration of specific phases of the cardiac cycle. These intervals help assess the timing and coordination of the heart's electrical impulses.
- Example: The PR interval includes the P wave and the PR segment, measuring the time from the onset of atrial depolarization to the start of ventricular depolarization. This interval is key in diagnosing atrioventricular (AV) conduction issues.
Intervals to Know:
By analyzing waveforms, segments, and intervals, clinicians can glean essential information about the heart’s electrical function, helping to diagnose a wide array of cardiac conditions and ensuring accurate and effective patient care.
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