Triệu chứng có thể được gây ra hoặc làm trầm trọng thêm bởi thuốc QT kéo dài và hạ kali máu. • Sự phổ biến của các sự kiện tim lúc nghỉ ngơi hoặc trong khi ngủ là thường thấy trong LQT2 và LQT3. • LQTS1 và LQTS2 có khả năng được triệu chứng. LQTS3 là nhiều khả năng gây tử vong. | Ventricular Tachycardia and Ventricular Fibrillation 171 Fig ECG LQTS1 T wave alternans. Symptoms may be caused or aggravated by QT prolonging drugs and hypokalemia. Occurrence of cardiac events at rest or during sleep is commonly seen in LQT2 and LQT3. LQTS1 and LQTS2 are likely to be symptomatic. LQTS3 is more likely to be lethal. LQT4 patients may have paroxysmal AF. Homozygous KVLQT1 and KCNE1 mutations are associated with congenital deafness Jarvell and Lange-Nielsen syndrome . Electrocardiographic features Electrocardiographic changes consist of prolongation of the QT interval corrected for the heart rate and measured in LII. Inpatients with LQTS1 T waves tend to be smooth and broad Fig. however it tends to be low amplitude and notched in LQTS2. Late onset but normal appearing T waves are seen in LQTS3. The QT interval corrected for the heart rate of 440 milliseconds in males and 460 milliseconds in females is considered abnormal. The QT interval becomes longer after puberty in females. The extent of QT prolongation does not correlate with symptoms. Marked prolongation of the QT interval more than 600 milliseconds may be associated with Tdp. T wave abnormalities are more noticeable in precordial leads. The appearance of notched T wave during the recovery phase of exercise is seen in LQTS patients but not in control subjects. QT dispersion is common in patients with LQTS. Dispersion of repolarization improves after anti-adrenergic therapy. The persistence of QT dispersion after beta-blocker therapy identifies high-risk patients. 172 Essential Cardiac Electrophysiology T wave alternans is a marker of electrical instability. It is generally seen during emotional or physical stress inpatients withLQTS. It identifies high-risk patients. Patients with LQTS may have sinus pauses and bradycardia. These changes may precede the occurrence of Tdp. Echocardiogram may show an increased rate of thickening in the early phase of systole and slowing of thickening and
