The most prevalent LQT1 form of inherited long QT syndrome is caused by mutations of the KCNQ1 gene resulting repolarizing I(Ks) potassium current to decrease and the QT interval to prolong. As abrupt sympathetic activation triggers ventricular arrhythmias that may cause syncopal attacks and sudden death in LQT1 patients, we investigated whether two known beta1-adrenergic receptor polymorphisms were associated with the duration of QT interval or history of symptoms in LQT1.
We determined beta1-adrenergic receptor polymorphisms (Ser49Gly and Arg389Gly) in 168 LQT1 patients. We also reviewed each patient's clinical records on the history of long QT syndrome-related symptoms and measured QT intervals from baseline ECG in each subject and from an exercise test ECG in 55 LQT1 patients.
Patients with the homozygous Arg389Arg genotype tended to have shorter and those with the Ser49Ser genotype longer QT intervals than patients with other genotypes, but neither polymorphism studied alone affected the risk of symptoms. In contrast, adjusted odds ratio for the history of symptoms was 4.9 (95% CI 1.18 to 20.3) in patients homozygous for both Ser49 and Arg389. These double homozygous patients showed similar QT intervals as the rest of the LQT1 cohort.
In this relatively small study, double homozygosity for Arg389 and Ser49 of the human beta1-adrenergic receptor associated with the risk of symptoms in LQT1. The association between these beta1-adrenergic receptor polymorphisms and the symptom history in LQT1 is not mediated via QT interval duration.
A comprehensive clinical and instrumental study involving the collection of complaints, resting ECG records, bicycler ergometry, Holter monitoring, echocardiography was performed in 80 Novosibirsk's residents (66 males and 14 females) aged 25-64 years who had the prolonged Q-T interval syndrome detected during a population survey. ECG frequently showed the early ventricular repolarization syndrome (23%) in males and left ventricular hypertrophy (36%) in females. Bicycle ergometry increased Q-T interval in 11% of males and decreased or unchanged it in the remaining cases. Holter monitoring revealed cardiac arrhythmias in 39% of males and 64% of females, supraventricular and monotopic ventricular premature beats being prevalent. The method was found to have advantages in detecting arrhythmias. Echocardiography performed in males made it possible to identify ventricular septum hypertrophy (40%) and mitral valve prolapse (20%). The examinees with the prolonged Q-T interval syndrome mostly had arterial hypertension, coronary heart disease, and alcoholic cardiomyopathy.
Long QT-interval is one of most important predictors of risk of development of life threatening arrhythmias and sudden death. Correct measurement of QT-interval is essential for diagnosis of its prolongation. At present the Bazett formula for calculation of corrected QT (QT(c) = QT/ radical (RR)) is a standard method of QT estimation. However historically in Russia calculation of predicted QT (QT(k) = k radical (RR)) QT(k) has become an accepted technique. Furthermore many authors in this country apply criteria created for QT(c) for interpretation of QT(k) values. This results in hyperdiagnosis of QT prolongation in unaffected persons, erroneous conclusions on harmless nature of this condition, and underestimation of risk in patients with real long QT syndrome. Thus it is vital to proclaim calculation of QT(c) an obligatory standard and to use existing international criteria for its interpretation.
The primary objective of this study was to determine the incidence of prolonged corrected QT (QTc) intervals in a population of geriatric psychiatry inpatients. Our secondary objective was to examine the associations between prolonged QTc intervals and risk factors identified as determinants in prolonging the QTc interval.
We identified all geriatric patients (aged 60 years and older) who were admitted to the geriatric program of our facility between May 1, 2003, and December 31, 2003. Those patients with a heart rate QTc interval calculated on the electrocardiogram (ECG) were eligible for the study. We used Bazett's formula to calculate the QTc interval. We defined a priori that a prolonged QTc interval would be 450 ms and 460 ms for men and women, respectively. We collected data on demographic variables such as weight, sex, age, and Axis I and III diagnoses, as well as on recognized risk factors for prolonged QTc interval. We used Student's t tests to conduct parametric analysis on continuous variables, and chi-square to test categorical variables for independence.
During the study period, 88 patients were admitted to the geriatric division of Riverview Hospital. Of these patients, 34 men and 42 women had calculated QTc intervals on their ECG and therefore made up the study population. Our data show that 29.4% of men and 21.4% of women had prolonged QTc intervals. However, neither diagnostic nor medicinal risk factors were found to be associated with an increased incidence of prolonged QTc interval in this patient population.
The preliminary findings of this study suggest that in this patient population the QTc interval may not be influenced by recognized risk factors to the same extent as observed in the adult population. These results warrant confirmation by a larger, prospectively designed study.
The incidence of lengthened Q-T interval in an open population of 45- to 54-year-old males was assessed in a random representative sample. Lengthened electrocardiographic Q-T interval was detected in 3.5% of cases. The identification of individuals with lengthened Q-T intervals at population screenings, their follow-up and the development of preventive measures against ventricular tachyarrhythmias and sudden death are shown to be warranted.
Genetic variants represent benign single-nucleotide polymorphisms, disease causing mutations or variants of unknown significance (VUS). Resting, exercise, and recovery QTc intervals have been utilized to detect long-QT syndrome (LQTS) mutations. We sought to provide clinical data that may assist in classifying the presented VUS as disease causing/benign and to determine whether resting and/or end-recovery QT parameters can evaluate the significance of VUS.
Twenty-six patients with a VUS in genes associated with LQTS (15 females, age 38 ± 16 years) and 26 age and gender matched controls (age 37 ± 20 years) were included. There were 10 VUS (5 KCNQ1, 4 KCNH2, 1 KCNE1) in 12 families. All but 1 VUS was associated with sudden cardiac death (SCD), aborted SCD or Torsade de pointes. A Schwartz score of =3.5 was observed in at least 1 family member with each VUS. Resting QTc was marginally longer in VUS patients compared with controls (458 ± 48 vs 437 ± 25, P = 0.052). A prolonged resting QTc (>470 ms males, >480 ms females) identified 6 VUS carriers and 1 control. VUS carriers had a substantially longer end-recovery QTc (502 ± 68 vs 427 ± 17, P 445 ms in 20/26 VUS patients compared to 2/26 controls (P
Epinephrine infusion may unmask latent genetic conditions associated with cardiac arrest, including long-QT syndrome and catecholaminergic polymorphic ventricular tachycardia (VT).
Patients with unexplained cardiac arrest (normal left ventricular function and QT interval) and selected family members from the Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER) registry underwent epinephrine challenge at doses of 0.05, 0.10, and 0.20 µg/kg per minute. A test was considered positive for long-QT syndrome if the absolute QT interval prolonged by = 30 ms at 0.10 µg/kg per minute and borderline if QT prolongation was 1 to 29 ms. Catecholaminergic polymorphic VT was diagnosed if epinephrine provoked = 3 beats of polymorphic or bidirectional VT and borderline if polymorphic couplets, premature ventricular contractions, or nonsustained monomorphic VT was induced. Epinephrine infusion was performed in 170 patients (age, 42 ± 16 years; 49% men), including 98 patients with unexplained cardiac arrest. Testing was positive for long-QT syndrome in 31 patients (18%) and borderline in 24 patients (14%). Exercise testing provoked an abnormal QT response in 42% of tested patients with a positive epinephrine response. Testing for catecholaminergic polymorphic VT was positive in 7% and borderline in 5%. Targeted genetic testing of abnormal patients was positive in 17% of long-QT syndrome patients and 13% of catecholaminergic polymorphic VT patients.
Epinephrine challenge provoked abnormalities in a substantial proportion of patients, most commonly a prolonged QT interval. Exercise and genetic testing replicated the diagnosis suggested by the epinephrine response in a small proportion of patients. Epinephrine infusion combined with exercise testing and targeted genetic testing is recommended in the workup of suspected familial sudden death syndromes. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00292032.
We took advantage of the genetic isolate of Finns to characterize a common long QT syndrome (LQTS) mutation, and to estimate the prevalence of LQTS.
The LQTS is caused by mutations in different ion channel genes, which vary in their molecular nature from family to family.
The potassium channel gene KCNQ1 was sequenced in two unrelated Finnish patients with Jervell and Lange-Nielsen syndrome (JLNS), followed by genotyping of 114 LQTS probands and their available family members. The functional properties of the mutation were studied using a whole-cell patch-damp technique.
We identified a novel missense mutation (G589D or KCNQ1-Fin) in the C-terminus of the KCNQ1 subunit. The voltage threshold of activation for the KCNQ1-Fin channel was markedly increased compared to the wild-type channel. This mutation was present in homozygous form in two siblings with JLNS, and in heterozygous form in 34 of 114 probands with Romano-Ward syndrome (RWS) and 282 family members. The mean (+/- SD) rate-corrected QT intervals of the heterozygous subjects (n = 316) and noncarriers (n = 423) were 460 +/- 40 ms and 410 +/- 20 ms (p
Mutations in five cardiac voltage-gated ion channel genes, including KCNQ1, HERG, SCN5A, KCNE1 and KCNE2, constitute the principal cause of inherited long-QT syndrome (LQTS). Typically, each family carries its own private mutation, and the disease manifests with varying phenotype and incomplete penetrance, even within particular families. We had previously identified 14 different LOTS-causing mutations in 92 Finnish families.
In order to complete the characterization of Finnish spectrum of LOTS genes, we conducted a systematic search for mutations in the five LOTS genes among 188 additional unrelated probands.
The screening was performed by denaturing high-performance liquid chromatography (dHPLC) and DNA sequencing.
Nineteen novel and 12 previously described mutations were identified. Collectively, these data extend the number of molecularly defined affected Finnish LOTS families and patients at present to 150 and 939, respectively. Four presumable founder mutations (KCNQ1 G589D and IVS7-2A > G, HERG R176W and L552S) together account for as much as 73% of all established Finnish LQTS cases.
The extent of genetic homogeneity underlying LOTS in Finland is unique in the whole world, providing a major advantage for screening and presymptomatic diagnosis of LOTS, and constituting an excellent basis to study the role of genetic and non-genetic factors influencing phenotypic variability in this disease.
BACKGROUND: Long QT syndrome is an inherited heart-rhythm disorder characterized by an increased risk of ventricular tachycardia and sudden death. Genetic testing is available. MATERIAL AND METHODS: The article is based on an anonymous family with a history of long QT syndrome, the authors experience with this patient group and a Pubmed search for literature from the period 1957 - 2007. RESULTS: An 8-year-old boy suffers syncope at a sports event, and this leads to genetic counseling and molecular genetic testing of his first-and second-degree relatives. Knowledge about genetic risk of sudden death in a family can trigger genetic testing and health preventive treatment of children, but can also have substantial psychosocial and ethical consequences for the family and for the health-care personnel involved. INTERPRETATION: Living with a genetic risk can be very emotionally challenging for the individuals and families, and "The Norwegian Act of Biotechnology in Human Medicine, etc" that regulates clinical genetic activities is extensive. An important question is whether the current Act allows communication of genetic information to persons other than the patient.