ABC Medical Notes.com

Related Subjects: | ECG-QT interval | Brugada Syndrome | Long QT syndrome (LQTS) Acquired | Long QT syndrome (LQTS) Congenital | Torsades de Pointes | Ventricular Fibrillation | Ventricular Tachycardia | Resuscitation - Adult Tachycardia Algorithm | Automatic Implantable Cardioverter Defibrillator (AICD)

BBs work by mitigating the adverse effects of sympathetic stimulation on the membrane ion channel. Sympathetic stimulation directly affects the QT interval, although this is mainly in LQT1 and LQT2.

About

• Congenital rare cardiac channelopathy disorder with prolongation of the QT interval on ECG
• Beta Blockers work by mitigating the adverse effects of sympathetic stimulation on the membrane ion channel. Sympathetic stimulation directly affects the QT interval, although this is mainly in LQT1 and LQT2.

Torsades

padding:10px">

Aetiology

• Mutations of genes for cardiac potassium, sodium, or calcium ion channels
• QT is a period of Ventricular repolarisation
• If prolonged acts as a substrate for arrhythmias
• Can lead to polymorphic VT (Torsades de pointes) and VF

Types

• Romano-Ward syndrome (autosomal dominant inheritance, QT prolongation, and ventricular tachyarrhythmias)
• Jervell and Lang-Nielsen (JLN) syndrome (autosomal recessive inheritance, congenital deafness, QT prolongation, and ventricular arrhythmias)

Risk factors

• Increased sympathetic tone

Clinical

• Asymptomatic, syncope, cardiac arrest, sudden death
• Symptoms may be with exertion and also at rest
• Events also associated with emotional events
• Family history of SCD important

Diagnostic Criterion

• QTc > 480 = +3 Points, QTc 460-469 = +2 Points, QTc 450-459 in male patient = +1 Point
• Torsade de pointes +2 Points
• T-wave alternans +1 Point
• Notched T wave in 3 leads +1 Point
• Low heart rate for age + 0.5 Points
• Syncope with stress + 2 Points without stress + 1 Point
• Congenital deafness + 0.5 Points
• Family members with definite LQTS + 1 Point
• Unexplained sudden cardiac death < 30 y in an immediate family member + 0.5 Points
• In the absence of medications or disorders known to affect these electrocardiographic features.

Investigations

• ECG, FBC, Electrolytes, Ca, Mg

Management

• Avoid drugs that prolong the QT interval or reduce their serum potassium or magnesium levels. Take supplements if needed. Potassium supplementation will increase serum potassium levels and may partially correct the repolarization abnormality in patients with LQT2. Two small studies showed that potassium supplementation with spironolactone resulted in significant QTc shortening
• Avoid competitive sports where diagnosis established by means of genetic testing only. Avoid swimming or water sports in LQT1 patients and reduction in exposure to abrupt loud noises (alarm clock, phone ringing, etc) in LQT2 patients. All LQTS patients should be disqualified from all competitive sports based on the QTc cutoff (>440 ms in males, >460 ms in females), whether symptomatic or asymptomatic
• Beta-blockers are effective in preventing cardiac events in approximately 70% of patients particularly those with LQT1. Propranolol, Metoprolol and Atenolol may be used.
• The implantable cardioverter-defibrillator (ICD) was shown to be highly effective to prevent sudden cardiac death (SCD) in high-risk patients. It is used in those with are patients who have survived a cardiac arrest, patients with syncope despite adequate Beta-blocker therapy (and LCSD), and some patients considered as high risk with a very long QTc interval (>550 ms), or signs of electrical instability such as T-wave alternans. Issues with ICDs are inappropriate shocks, lead problems, vascular occlusion, infection, psychological adjustment, and social discrimination
• Left cervicothoracic stellectomy is used in high-risk patients with LQTS but is rarely used but it is almost as effective as ICD and less comorbidity. Whenever cardiac events recur in patients on beta-blockers, LCSD should be strongly considered.

References

Management of Patients with Long QT Syndrome. Korean Circ J. 2016 Nov; 46(6): 747-752.