Anesthesia Pharmacology Chapter 15:  Cardiac Anesthesiology

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"Effect of Sevoflurane on QT Interval in a Patient with Congenital Long QT Syndrome"

1Gallagher, JD, Weindling, SN, Anderson, G, Fillinger, MP, Effect of Sevoflurane on QT Interval in a Patient with Congenital Long QT Syndrome, Anesthesiology, 1998 December; 89(6) 1569-1573

2 QT Interval and QT Interval Prolongation

  • The QT interval is defined as the time between the start of the QRS complex and the end of the T wave in the ECG  and corresponds to the duration between depolarization onset myocardial repolarization. QT interval measurements vary depending upon which ECG lead is used since this "T wave dispersion" occurs when the terminal portion of the T wave is isoelectric in some leads. If multiple leads are used,  the longest QT interval is considered to be the true QT interval.

  • QT interval dependency includes: heart rate, age and gender. Sympathetic tone variation is probably responsible for QT interval diurnal variation. 

  • Measured QT (QTo) interval can be corrected (QTc) for heart rate by using the following formula where RR is the interval in seconds between two successive R waves on the ECG.

    • QTc = QTo ()

  • Prolongation of the QTc interval indicated prolonged ventricular repolarization which may lead to  early afterdepolarization (EADs) which trigger a polymorphic ventricular tachycardia, (torsade de pointes). 

    • Torsade de pointes presents (ECG) as alternating electric polarity, periodic twisting of the points of the QRS complex around the isoelectric line and heart rates of 200-250.   The arrhythmia is typically self-terminating, but can evolve to ventricular fibrillation or less often sustained ventricular tachycardia.Torsades  may result in dizziness, syncope, cardiac arrest and death

  • Management of torsade de pointes due to long QT syndrome

    • .If torsade de pointes has hemodynamic consequences prompt termination of the abnormal rhythm may be indicated . 

      • Defibrillation is usually effective. 

      • Infusion of magnesium or acceleration of the heart rate with rapid pacing or isoproterenol infusion can be useful. 

      • "Patients with proven congenital or idiopathic long QTc syndrome who have a history of cardiac arrest, syncope, documented torsade de pointes or a family history of sudden death at a young age are usually treated with an implantable cardiac defibrillator."

3The 1993 Diagnostic Criteria of Schwartz et al for the Long QT Syndrome

Parameter

Finding

Points

clinical history of syncope

none

0

 

without stress

1

 

with stress

2

congenital deafness

absent

0

 

present

0.5

family history of long QT syndrome

absent

0

 

present

1

unexplained sudden death in an immediate family member before age 30

absent

0

 

present

0.5

corrected QT interval

< 450 msec

0

 

450 msec (in males)

1

 

460-470 msec

2

 

>= 480 msec

3

torsade de pointes

absent

0

 

present

2

T wave alternans

absent

0

 

present

1

leads with notched T waves

>= 3

1

 

< 3

0

heart rate for age

low (< 2nd percentile for age)

0.5

 

not low

0

  • Torsade de pointes and syncope are mutually exclusive.

  • The same family member cannot be used to satisfy a family history of LQTS and sudden death.

  • The heart rates for age in children are given by Davignon et al (1980).

  • The ranges for corrected QT interval given in the original table do not cover a number of situations: (a) female with interval 450 msec; (b) range 451-459; (c) range 471-479. I have set (a) to 0 points; (b) to 1 point; (c) to 2 points in the implementation.

  • total score =MAX((points for syncope) (points for torsade on ECG)) + SUM(points for remaining parameters)

    • Interpretation:minimum score: 0; maximum score: 9.5

Total Score

Probability of LQTS

<= 1

low

2 to 3

intermediate

>= 4

high

  • Schwartz PJ Moss AJ et al. Diagnostic criteria for the long QT syndrome. An update. Circulation. 1993; 88: 782-784

  • Davignon A Rautaharju B et al. Nomral ECG standards for infants and children. Pediatr Cardiol. 1980; 1: 123-130.

  • Khan IA. Long QT syndrome: Diagnosis and management. Am Heart J. 2002; 143: 7-14

V5 ECG Recordings (Fig 1 from reference 1)

  • Paper speed: 25 mm/sec; amplitude 1mV/ division.  

  • Prior to sedation, QT interval = 362 msec (QTc = 396 msec)

  • A: Initial ECG following midazolam sedation [QT interval 0.39 sec; QTc = 0.405 sec]

  • B:  ECG taken during inhalation of nitrous oxide and following tracheal intubation, but PRIOR to sevoflurane. This strip illustrates occasional monoform extrasystoles [QT = 0.38 sec; QTc = 0.434 sec]

V5 ECG Recordings (Fig 1 from reference 1)

  • Paper speed: 25 mm/sec; amplitude 1mV/ division.  

  • C. During sevoflurane inhalation, QT prolongation to 0.43 sec (QTc = 0.467 sec) is noted

  • D.  One minute following extubation, frequent multiform ventricular extrasystoles were noted despite QTc shortening to 0.423 sec.  QTc determined when no extrasystoles were exhibited.

  • E:  Rhythm following IV labetalol; QT interval = 0.37 sec; QTc = 0.432 (absence of arrhythmias)

QTcinterval and heart rate in a patient with idiopathic long QT syndrome--Sevoflurane Effects (Fig 2 from Reference 1)

 

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