ECG Rhythm Interpretation 2_Reading 12 lead ECG

Posted by e-Medical PPT Wednesday, September 1, 2010
The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. It is usually 120 to 200 ms long. On an ECG tracing, this corresponds to 3 to 5 small boxes. The PR interval reflects the time the electrical impulse takes to travel from the sinus node through the AV node and entering the ventricles. The PR interval is therefore a good estimate of AV node function.
Variations in the PR interval can be associated with certain medical conditions:
  1. Long PR interval (of over 200 ms) may indicate a first degree heart block.
  2. Prolongation can be associated with hyperkalemia or acute rheumatic fever.
  3. Short PR interval may indicate a pre-excitation syndrome via an accessory pathway that leads to early activation of the ventricles, such as seen in Wolff-Parkinson-White syndrome.
  4. Variable PR interval may indicate other types of heart block
The QRS complex is a name for some of the deflections seen on a typical electrocardiogram (ECG).A Q wave is any downward deflection after the P-wave. An R-wave is an upward deflection and the S wave is any downward deflection after the R-wave.The His/Purkinje specialized muscle cells coordinate the depolarization of both ventricles and if they are working efficiently the QRS complex is 80 to 120 ms in duration.The duration, amplitude, and morphology of the QRS complex is useful in diagnosing cardiac arrhythmias, conduction abnormalities, ventricular hypertrophy, myocardial infarction, electrolyte derangements, and other disease states.
The QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle. A prolonged QT interval is a risk factor for ventricular tachyarrhythmias and sudden death.The QT interval is dependent on the heart rate in an obvious way (the faster the heart rate, the shorter the QT interval) and may be adjusted to improve the detection of patients at increased risk of ventricular arrhythmia.

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