-LQT1 a single, smooth, broad-based T wave is common, as well as a late onset
normal-appearing T wave
-LQT2, bifid T waves are a hallmark ECG feature
-LQT3, the T waves are typically late-onset, prominent, and usually peaked. Long ST (similar to hypocalcemia). Rx: Ranolazine
Affects 1/2000. AD (Romano Ward Sd) or ar version very rare 1/million (Jarvell Lange Nielsen Sd)
The cardiac phenotype is always AD RWS 50 % chance of inheriting the disease mutation but whether the patient will show it
depends on a lot of factors. ECG is profound QT prolongation which could be LQTS. Differential includes Cesium toxicity.
Syncope - Seizures - Sudden death (50% are asymptomatic)
Vulnerable period of time: post partum (sleep deprivation, auditory triggers)
Sudden onset, during exercise, auditory trigger => warning sign until further evaluation
Highest predictor of death.
Lead II and V5 are QT friends. Don't look anywhere else, if your QT matches computer's then trust Bazett if not, calculate yourself.
In sinus arrhythmia do not use your longest QT wherever you find it and shortest R-R you will tremendously overestimate your QTc.
Concealed (long QT interval) LQTS grey zone
below. QTc > 460 ms is too long. Women have
10 ms longer on average QT than men.
40% of LQT individuals are concealed. < 1% PPV for LQTS with these guidelines (95th percentile)
Woman with QTc 460, likelihood of having LQTS is < 0.1%. If no story and her QTc is 480, likelihood is 4%.
If Asx child of parent with LQT1, QTc=440 ms, likelihood of having LQTS is ~50%
If TdP while swimming and QTc> 500 ms => 100% LQTS
STORY DEPENDENT: when there is an index of suspicion, story, then is the time to pursue genetic testing.
2/3 of all LQTS is due to loss of function mutation in one of two voltage-gated Na channels IKs or IKr
Location and function of genetic mutations matters with HR>2 independent of traditional RF
Type 1 LQTS is most common (30-35%) IKs loss of function due to mutation in gene KCNQ1 - swimming
Type 2 LQTS is 25-30% due to IKr loss function and mutation in gene KCNH2 - auditory
Type 3 LQTS 5-10% is Na channel disease mutation in SCN5A - sleep
All drugs that prolong QT further are all K channel blockers
1-wide based. 2-notch looking. 3- normal QT after prolonged ST segment
1-Swimming, exercise. 2-Post partum women, auditory triggers. 3-Sleeping
This is not an ICD disease. Most benefit with BB. Caution in non selective BB atenolol and metoprolol
LQT1-2: nadolol or propranolol. LQT3: propranolol +/- mexiletine/ranolazine
Family history is an emotional Risk Factor for LQTS not evidence based factor (unlike HCM)
When you remove the left sympathetic chain it has a potent antifibrillatory effect
Renewed use of Flecainide.
Yield of genetic testing: < 20% SQTS - 35% for Brugada - 60% CPVT - 75% LQTS
Certain genetic variants such as the Jarvell-Nielsen Syndrome and the
extremely rare Timothy Sd (LQT8) are highly malignant, manifest with
arrhythmic events very early, and respond very poorly to therapies.
Clinically, there are several patterns associated with high risk:
-QTc> 500 ms
-Homozygous mutations (JNS)
-Overt T wave alternans, especially evident despite proper therapy is a
marker of electrical instability
-Patients who had syncope or cardiac arrest in the first year of life.
-Concealed mutation positive patients are at 10% risk of an arrhythmic
event between birth and age 40.