Google

Monday, September 29, 2008

Long QT Syndrome :

    Long QT Syndrome :

    http://www.emedicine.com/med/topic1983.htm

  1. Long QT syndrome (LQTS) is a congenital disorder characterized by a prolongation of the QT interval on ECG and a propensity to ventricular tachyarrhythmias, which may lead to syncope, cardiac arrest, or sudden death
  2. The QT interval on the ECG, measured from the beginning of the QRS complex to the end of the T wave, represents the duration of activation and recovery of the ventricular myocardium. QT intervals corrected for heart rate (QTc) longer than 0.44 seconds are generally considered abnormal, though a normal QTc can be slightly prolonged in female individuals (up to 0.46 sec).
  3. The Bazett equation is used to calculate the QTc, as follows: QTc = QT/root of the R-R interval
  4. To measure QT interval accurately, the relationship of QT to the R-T interval should be reproducible. This issue is especially important when the heart rate is <50>120 bpm and when athletes or children have marked beat-to-beat variability of the R-R interval. In such cases, long recordings and several measurements are required
  5. Prolonged recovery from electrical excitation increases the likelihood of dispersing refractoriness, when some part of myocardium might be refractory to subsequent depolarization.
  6. QT prolongation can lead to polymorphic ventricular tachycardia, or torsade de pointes, which itself may lead to ventricular fibrillation and sudden cardiac death.
  7. LQTS has been recognized as mainly
    1. Romano-Ward syndrome (ie, familial occurrence with autosomal dominant inheritance, QT prolongation, and ventricular tachyarrhythmias) or
    2. Jervell and Lang-Nielsen (JLN) syndrome (ie, familial occurrence with autosomal recessive inheritance, congenital deafness, QT prolongation, and ventricular arrhythmias).
  8. LQTS is caused by mutations of the genes for cardiac potassium and sodium or calcium ion channels
  9. LQTS usually present with cardiac events in childhood, adlescence, or early adulthood.
  10. The risk of death from LQTS is higher in boys than in girls younger than 10 years, and the risk is similar in male and female patients thereafter.
  11. Diagnostic Criteria for LQTS
  12. Criterion

    Points

    ECG findings*

    QTc, ms†

    >480

    3

    460-470

    2

    450 in male patient

    1

    Torsades de pointes‡

    2

    T-wave alternans

    1

    Notched T wave in 3 leads

    1

    Low heart rate for age§

    0.5

    Clinical history

    Syncope||

    With stress

    2

    Without stress

    1

    Congenital deafness

    0.5

    Family history

    A. Family members with definite LQTS#

    1

    B. Unexplained sudden cardiac death <30>

    0.5

    *In the absence of medications or disorders known to affect these electrocardiographic features.

    †QTc calculated by Bazett's formula

    ‡Mutually exclusive

    §Resting heart rate below the second percentile for the age.

    ||Mutually exclusive

    ¶The same family member cannot be counted in A and B.

    #Definite LQTS is defined by an LQTS score of more than 3 (>4).

    Adapted from Circulation. 1993;88:782-84.

  13. Definition of QTc Based on Age- and Sex-Specific Criteria
  14. Group

    Prolonged QTc, s

    Borderline QTc, s

    Reference Range, s

    Children and adolescents (<15>

    >0.46

    0.44-0.46

    <0.44

    Men

    >0.45

    0.43-0.45

    <0.43

    Women

    >0.46

    0.45-0.46

    <0.45

  15. Beta-blockers are drugs of choice for patients with LQTS. The protective effect of beta-blockers is related to their adrenergic blockade that diminishes the risk of cardiac arrhythmias. They may also reduce the QT interval : Propranolol Nadolol Metoprolol Atenolol

2 comments:

Vickie said...

My daughter died from this condition at the age of 20. She started showing signs of LQT at age 11. She was taking beta blockers. She was not able to get pacemaker as she would be getting too many shocks. She died from getting too excited and bending over. Most family members were tested at the time with EKG as this was the only means testing. No one has shown signs of LQT.

New bie said...

most of the people with this condition doesnt have any symptoms, specific like that of other cardiac problems, but this is identified in most of the cases accidentally by ECG, but if at all if the symptoms are to be quoted, then thay shall be like fainting, frequent head ache, palpitations