Is a disorder of myocardial depolarisation characterised by prolonged QT interval on ECG & ventricular arrhythmia.
Usually torsades de pointes that lead to sudden cardiac arrest.
QT prolongation can be congenital or acquired (1) advance in molecular biology revealed that ion channels that generate electrical activity of heart are defective in congenital LQTS.
Mutations of cardiac ion channel genes
☛4 types of Romana – ward syndrome
☛ 2 types of Jervell – Jonge Nielsen syndrome
☛ 2 additional synd. Anderson tavil & timothy
☛ LQT1 / LQT2 – K+ channel -42% incidence
☛ LQT3 – Na+ -45% incidence
☛ LQT4 – Na/Ca Exchanger
☛ LQT5 / T6 – K+ channel
The QT interval on ECG represent duration of activation & recovery of ventricular myocardium.
Prolonged recovery from electrical excitation contributes to an ↑ likelihood of dispersion of refractorinesss when some part of myocardium might be refrcrtory to subsequent depolarisation.
So a wave of excitation may pursue a distinctive pathway around a focal point in myocardium leading to VT.
Arrhythmic response in pts. with LQTS can be precipitated by a variety of adrenergic stimuli including exercise, emotion, loud noise & swimming but it may also occur without such preceding conditions.
Clinical manifestations –
- Clinical history (+) in 60% families
- Deafness present -5%
- Presenting symptoms syncope (26%), seizure (10%), cardiac arrest (9%),presyncope / palpitations( 6%)
- Major occur during exercise or with emotion
- Manifest by end of second decade.
- Syncope occur in intense adrenergic arousal,intense emotion & during rigorous exercise,swimming appears to be particular trigger among exercise.
Abrupt auditory signals such as loud door bell,alarm clock, telephone or security alone trigger symptoms
- Prolonged QT Interval with QTc > 0.46 sec
- Abnormal T ware morphology, bifid, diphasic or notched
- Brady cardia (20%) second degree AV block, Multiform PVCs, monomrphic & polymorphic VT (10% – 20%)
- Echo – Normal Heart
- Trademill test – prolongation of QTC int. in response to exercise.
Vent – arrhythmias may develop drug test.
- Holter monitoring- prolongation of QTC Int.
Shwartz diagnostic Criteria for long QTC syndrome-
> 480sr. 3
460 – 470 2
450 (male) 1
Torsade de pointes 2
T wave alternans 1
Notched T wave in 3 leads 1
Low heart rate for age 0.5
With stress 2
With ent stress 1
With defi. LQTS 1
Unexplained death 0.5
<1 – 1ow probability
2 – 3 – intermediate
>4 – High
- Epinephris test
- Genetic testing
- Risk factors for LQTS
- QTC > 0.55
- Sym at presentation syncope,seizure ,cardiac arrest
- Young age at presentation < 1M
- Documented torsades de pointesb
- T wave alternans
- Noncompliance with medication
- β blocker – T/t of choice propranolol, atenolol, metaprolol. They reduce rate,syncope & sudden cardiac death.
Don’t change QTC interval
70% Pts – effective
- cardiac pacemaker
- Lt cardiac sympathetic denervation
- Targeted pharmacological therapy
- Gene specific approach