Satyendra Dhar, MD @DharSaty · 2 years ago
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QT/QTc- Interval • Start of Q-wave to end of the T-wave (time of ventricular depolarization + repolarization). • Life threatening
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QT/QTc- Interval
•	Start of Q-wave to end of the T-wave (time of ventricular depolarization + repolarization).
•	Life threatening risk of prolonged QTc >500ms = Torsades de pointes (TdP)
•	Prolonged QT/QTc interval may be a clue to electrolyte disturbances (hypocalcemia or hypokalemia), drug effects (quinidine, procainamide, amiodarone, or sotalol), or myocardial ischemia (usually with prominent T wave inversions). 
•	Shortened QT intervals are seen with hypercalcemia and digitalis effect. 
•	Each 10-millisecond increase in QTc contributes approx a 5% to 7% additional increase in risk for TdP.
•	QTc of 540 milliseconds has a 63% to 97% higher risk of developing TdP than a patient with QTc of 440 milliseconds.

How do you measure it:
•	Find a lead with the tallest T wave and count the little boxes from the start of the QRS complex to the point where the T wave comes back down to the isoelectric line. 
•	Multiply the number of little boxes by 0.04 seconds. 
•	Example if you counted 8 boxes then QT interval is 8 x 0.04 = 0.32 seconds (320 milliseconds).
•	QT interval should be less than half the preceding R-R interval (Works for regular rates between 65-90).

Methods of calculating the QTc:
•	Bazett formula, QTc = QT / √RR.  
•	Fridericia formula (QTc = QT / RR1/3)
•	Hodges [QTc = QT + 0.00175 x (HR - 60)]
•	Framingham linear regression analysis {QTc = QT + 0.154 x (1 - RR)}
•	Karjalainen et al. [QT nomogram] 
•	Rautaharju formula, QTc = QT x (120 + HR) / 180

#QTInterval #QTc #Torsadesdepointes #TdP #Bazettformula #Fridericiaformula 
#Hodgesformula #Framinghamanalysis #Karjalainen #QTnomogram #Rautaharjuformula #QT
Satyendra Dhar, MD @DharSaty · 2 years ago
Hospital Medicine Clinical Assistant Professor The content and images on this website are provided for educational and informational purposes only and are not a substitute for professional medical advice, diagnosis, or treatment. The views expressed are those of the authors and do not necessarily reflect those of any affiliated institutions. While efforts are made to ensure accuracy and currency, medical knowledge is continually evolving, and errors or omissions may occur. Users are advised to independently verify information and seek guidance from qualified healthcare professionals for any medical decisions. By using this website, you acknowledge responsibility for your own clinical judgments, and the website and its contributors disclaim any liability arising from the use of its content. 👉 Follow 'Medical Infographics' on 👉 https://www.DharSaty.com
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