QT interval, long

A disease predisposing those affected to severe cardiac arrhythmia. The term long QT syndrome refers to an abnormality found in the electrocardiograms of the patients a long QT interval caused by a prolonged... 

Domperidone minimally crosses the BBB it acts in the CTZ which lies outside of the BBB. As such, domperidone is less likely to cause the centrally-mediated adverse effects seen with metoclopramide and has an estimated overall incidence of 5% to 10%.1,30 However, domperidone has been associated with prolonged QT intervals, cardiac arrhythmias, and sudden death.31 It should not be used for patients with underlying long QT interval or for those on other medications that prolong the QT interval. Both metoclopramide and domperidone can cause hyperprolactinemia, galactorrhea, and gynecomastia. 

TdP is characterized by long QT intervals or prominent U waves on the surface ECG. 

The Class III effects of amiodarone develop over several weeks. This time-course is similar to that seen in thyroid gland ablation [25]. It is well known that patients with hypothyroidism have long QT intervals which are indicative of prolonged action potentials. Amiodarone has been shown to inhibit the conversion of thyroxine (T4) to triiodothyronine (T3) both in human subjects [26] and in vitro [27]. It has been argued that the Class III effects of amiodarone are due to its effects on thyroid hormones [28]. Others, however, argue that there is no relationship between prolongation of ventricular refractory period by amiodarone and thyroid state [29]. 

Antzelevitch C, Sun Z-Q, Zhan Z-Q, Yan G-X (1996) Cellular and ionic mechanisms underlying erythromycin-induced long QT intervals and Torsade de Pointes. J Am Coll Cardiol 28 1836-1848... 

There has been a report of ventricular fibrillation during fexofenadine administration in a man with a preexisting long QT interval (6). However, causality between fexofenadine and the cardiac effects was unclear. 

Olivier C, Rizk C, Zhang D, Jacqz-Aigrain E. Allongement de I espace OT compliquant la prescription d halofantrine chez deux enfants presentant un acces palustre a plasmodium falciparum. [Long QT interval complicating halofantrine therapy in 2 children with Plasmodium falciparum malaria.] Arch Pediatr 1999 6(9) 966-70. 

DiSegni E, Klein HO, David D, Libhaber C, Kaplinsky E. Overdrive pacing in quinidine syncope and other long QT-interval syndromes. Arch Intern Med 1980 140(8) 1036-40. 

In a survey of 1288 patients taking sotalol, dysrhythmias occurred in 56, in 24 cases torsade de pointes (3). There was no relation between these dysrhythmias and previously associated factors, such as bradycardia, a long QT interval, and hypokalemia, but in patients on hemodialysis even a low dosage (40 mg bd) can be associated with torsade de pointes (6). Similar prodysrhythmic effects have been reported in children (7). 

Of 98 patients with drug-induced long QT interval, one taking sulfamethoxazole carried a single-nucleotide polymorphism (SNP found in about 1.6% of the general population) in KCNE2, which encodes MinK-related peptide 1 (MiRPl), a subunit of the cardiac potassium channel iKr (12). Channels with the SNP were normal at baseline but were inhibited by sulfamethoxazole at therapeutic concentrations, which did not affect wild-type channels. 

Figure 3.32 Female, 75 years old, with stroke. Note the large negative T wave with a quite wide base nearly without ST segment and a quite long QT interval (>500 ms). The patient died a few hours later.

Figure 4.55 A 20-year-old patient with chronic renal failure submitted to periodical haemodialysis during last years, presenting with significant hypertension (230/130). The potassium level is elevated (6.4 mEq/L). Observe a tall and peaked T wave, as well as the ST-segment elevation in V2-V3. A relatively long QT interval is due to the ST-segment lengthening produced by coexisting hypocalcaemia (see V6 and I).

The onset of quinidine syncope is associated with a long QT interval, and includes lightheadedness, fainting, and an oscillatory cardiac rhythm known as torsades de pointes. 

QT interval prolongation. Congenital long QT interval syndrome was confirmed by genetic testing. 

Class lib indications for an ICD (1) Patients optimally managed with New York Heart Association Functional Class I heart failure and nonischemic cardiomyopathy who have a left ventricular ejection fraction <0.35. (2) Syncope of unclear etiology and ECG evidence of Brugada syndrome. (3) Patients with congenital long QT interval syndrome who have reasonable expectation of survival. 

ICD placement in patient with nonsustained ventricular tachycardia, history of coronary artery disease, left ventricular dysfunction, and an inducible ventricular arrhythmia at an electrophysiology study is indicated as per MADIT criteria. However, these data are supplanted by SCD-HeFT which indicates that an ICD implant is appropriately independent of electrophysiology test results. A controversial area is ICD implantation in patients without structural heart disease who have spontaneous sustained ventricular tachycardia that is not amenable to medical therapy. We do not ascribe to this indication based on lack of data indicating the need for an ICD unless the ventricular tachycardia is polymorphic associated with evidence for a channelopathy such as long QT interval. 

Comparisons of the incidence of the congenital syndromes show that short QT syndrome is much rarer than long QT syndrome, similar to the findings of short QT intervals compared with long QT intervals in the general population. 

Fonseca F, Marti-Almor J, Pastor A, Cladellas M, Farre M, de la Torre R, Torrens M. Prevalence of long QT interval in methadone maintenance patients. Drug Alcohol Depend 2009 99 327-32. 

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