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Conduction: Difference between revisions
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→The PQ interval
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The PQ interval (sometimes referred to as the PR interval as a Q wave is not always present) indicates how fast the action potential is transmitted through the AV node (atrioventricular) from the atria to the ventricles. Measurement should start at the beginning of the P wave and end at the beginning of the QRS segment. | The PQ interval (sometimes referred to as the PR interval as a Q wave is not always present) indicates how fast the action potential is transmitted through the AV node (atrioventricular) from the atria to the ventricles. Measurement should start at the beginning of the P wave and end at the beginning of the QRS segment. | ||
'''The normal PQ interval is between 0.12 and 0. | '''The normal PQ interval is between 0.12 and 0.22 seconds'''. | ||
A prolonged PQ interval is a sign of a degradation of the conduction system or increased vagal tone (Bezold-Jarisch reflex), or it can be pharmacologically induced. | A prolonged PQ interval is a sign of a degradation of the conduction system or increased vagal tone (Bezold-Jarisch reflex), or it can be pharmacologically induced. | ||
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During ventricular pacing this method overestimates the QTc. The Framingham formula performs better during pacing, but still overestimates the QTc in sinus | During ventricular pacing this method overestimates the QTc. The Framingham formula performs better during pacing, but still overestimates the QTc in sinus rhythm (in the same patient) by about 37-43 msec.<cite>Chiladakis</cite> | ||
In a pathological prolonged QT time, it takes longer than the normal amount of time for the myocardial cells to be ready for a new cycle. There is a possibility that some cells are not yet repolarized, but that a new cycle is already initiated. These cells are at risk for uncontrolled depolarization, induction of [[Torsade de Pointes]] and subsequent [[Ventricular Fibrillation]]. | In a pathological prolonged QT time, it takes longer than the normal amount of time for the myocardial cells to be ready for a new cycle. There is a possibility that some cells are not yet repolarized, but that a new cycle is already initiated. These cells are at risk for uncontrolled depolarization, induction of [[Torsade de Pointes]] and subsequent [[Ventricular Fibrillation]]. | ||