Interpreting ECG Flashcards
What does the p wave in an ECG represent?
Represents Atrial Depolarisation
What is the relationship between ECG P-wave and cardiac anatomy and Physiology?
A normal P-wave indicates normale atrial depolarisation.
Depolarization of the atria begins near the SA node and progresses across the atria from right to left and downwards.
The first part of the P-wave represents depolarization of the right atrium; the second part represents depolarization of the left atrium.
What does the QRS complex in an ECG represent?
Represents Ventricular Depolarization
What does the T-wave in an ECG represent?
Represents Ventricular Repolarisation
What is the relationship between ECG QRS complex and cardiac anatomy and Physiology?
A normal QRS represents normal depolarization of the ventricles.
The first part of the QRS complex, usually the Q wave represents depolarization of the interventricular septum; the rest of the QRS represents the simultaneous depolarization of the right and left ventricles
What is the relationship between ECG T-wave and cardiac anatomy and Physiology?
A normal T-wave represents normal repolarization of the ventricles; beginning at the epicardial surface of the ventricles and progress inwardly through the ventricular walls to the endocardial surface
What is the normal duration of a P-wave?
0.06 - 0.12 secs
What does the PR interval in an ECG represent?
Represents atrioventricular conduction time
Normal PR interval represents the onset of atrial depolarization and the onset of ventricular depolarisation
What is the normal duration of PR interval?
0.12 - 0.20 secs
What is the relationship between ECG PR interval and cardiac anatomy and Physiology?
Indicates that the electrical impulse originated in the SA node has progressed normally through the electrical conduction system and through the AV node and bundle of His without delay
What is the normal duration of QRS Complex?
0.04 - 0.12 secs
What does an Abnormal PR interval indicate?
Longer than 0.20 secs - represents delayed progression of the electrical impulse through the AV node
Less than 0.12 secs - may represent that the electrical impulse originated closer to the AV node (may be an ectopic pacemaker or escape pacemaker)
What does an Abnormal QRS Complex indicate?
Represents abnormal depolarization of the ventricles
May be due to:
- Interventricular Conduction Disturbances (BBB)
- Aberrant Ventricular Conduction
- Ventricular Ectopic or Escape Pacemaker
What does the ST segment in an ECG represent?
Represents the end of ventricular depolarization and the beginning of ventricular repolarization
What does an Abnormal ST Segment indicate?
If the ST segment appears depressed or elevated it indicates early T-wave repolarization
If Depressed - Significant =2mm in 2 continuous leads
If Elevated - Significant = 1mm
What does a Normal ST segment look like?
Isoelectric in all three views of the heart:
Inferiorly
Anteriorly
Laterally
What is the normal duration of QTc?
Less than 0.44 secs
What is Bazett’s Formula?
QTc = QT/sqrt RR
What does the QT interval in an ECG represent?
Represents the refractory period of the ventricles, during which they depolarize and repolarize
Describe the Refractory Period?
The time between the onset of depolarization and the end or repolarization
Divided into Absolute Refractory and Relative Refractory
Describe where the Absolute Refractory takes place and what it represents?
It is from the beginning of the QRS to the peak of the T-wave.
Cardiac cells cannot be stimulated to depolarize
Describe where the Relative Refractory takes place and what it represents?
It is from the peak of the T-wave to the end of the T-wave.
Cardiac cells can be stimulated if the stimulus is strong enough
What is the Cardiac Axis??
The cardiac axis is the average direction the depolarization wave spreads through the heart
The left ventricle has a greater influence than the right on the cardiac axis as it has more muscle mass
The QRS will be positive in a lead when the depolarization wave is moving towards that lead
Describe the Normal Cardiac Axis?
This occurs when the average spread of depolarization moves from high in the right atrium to the apex of the ventricles (Imagine 11 o’clock to 5 o’clock)
Which leads should be analyzed when determining the Cardiac Axis?
Lead I followed by aVF
Lead II may be necessary if one of the above are negative
