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Diagnostic Testing: Difference between revisions
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Thus at a heart rate of 60 beats per minute, the RR interval is 1 second and the QTc equals QT/1. The QTc calculator can be used to easily calculate QTc from the QT and the heart rate or RR interval. | Thus at a heart rate of 60 beats per minute, the RR interval is 1 second and the QTc equals QT/1. The QTc calculator can be used to easily calculate QTc from the QT and the heart rate or RR interval. | ||
On modern ECG machines, the QTc is given. However, the machines are not always capable of making the correct determination of the end of the T wave. Therefore, it is important to check the QT time manually [ http://en.ecgpedia.org/wiki/Conduction | On modern ECG machines, the QTc is given. However, the machines are not always capable of making the correct determination of the end of the T wave. Therefore, it is important to check the QT time manually [http://en.ecgpedia.org/wiki/Conduction Conduction]. Most QT experts define the end of the T wave as the intersection of the steepest tangent line from the end of the T-wave with the base line of the ECG. | ||
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 repolarised, 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 repolarised, 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. | ||
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[[Image:Apical_4_chamber_view.gif|thumb|300px|Figure 4. Apical four chamber view by two dimensional echocardiography. Source: http://commons.wikimedia.org/wiki/File%3AApical_4_chamber_view.gif]] | [[Image:Apical_4_chamber_view.gif|thumb|300px|Figure 4. Apical four chamber view by two dimensional echocardiography. Source: http://commons.wikimedia.org/wiki/File%3AApical_4_chamber_view.gif]] | ||
[[Image:LeftVentricleShortAxis.gif|thumb|300px|Figure 5. Short axis view of left ventricle by two dimensional echocardiography. Source:http://commons.wikimedia.org/wiki/File%3ALeftVentricleShortAxis.gif]] | [[Image:LeftVentricleShortAxis.gif|thumb|300px|Figure 5. Short axis view of left ventricle by two dimensional echocardiography. Source: http://commons.wikimedia.org/wiki/File%3ALeftVentricleShortAxis.gif]] | ||
In addition, in the cross sectional planes ventricular wall motion and left ventricular wall thickening during systole (an important measure of myocardial viability) can be investigated. The systematically assessment of cross sectional segment can also be used to estimate left ventricular volumes and ejection fraction. [Figure 6] | In addition, in the cross sectional planes ventricular wall motion and left ventricular wall thickening during systole (an important measure of myocardial viability) can be investigated. The systematically assessment of cross sectional segment can also be used to estimate left ventricular volumes and ejection fraction. [Figure 6] | ||