Prolonged-QT-interval

(NEJM 2008;358:169; <www.torsades.org>)

參考 ➡️ Long-QT syndrome

Prolonged QT interval (NEJM 2008;358:169; <www.torsades.org>)

• Measure QT using threshold method (start of QRS to end of Tw at ↣ isoelectric line) or tangent (QRS to where tangent of Tw downslope intersects baseline) when long tail. Use longest QT (often V2 or V3) and omit U wave (Circ 2018;138:2345).

• QT varies w/ HR → corrected w/ Bazett formula: (RR in sec), overcorrects at ↣ high HR, undercorrects at ↣ low HR (nl QTc <450 msec ♂, <460 msec ♀)

• Fridericia’s formula preferred at ↣ very high or low

• QT prolongation a/w ↑ risk TdP (espec >500 msec); establish baseline QT and monitor if using QT prolonging meds, no estab guidelines for stopping Rx if QT prolongs

Etiologies of Prolonged-QT-interval