The spectrum of symptoms and QT intervals in carriers of the gene for the long-QT syndrome

Deleting the accessory subunit KChIP2 results in loss of I(to,f) and increased I(K,slow) that maintains normal action potential configuration

BACKGROUND

Four voltage-gated potassium currents, I(to,f) (K(V)4.2), I(to,s) (K(V)1.4), I(K,slow) (K(V)1.5+K(V)2.1), and I(SS) (TASK1), govern murine ventricular repolarization. Although the accessory subunit KChIP2 influences I(to,f) expression, in preliminary experiments we found that action potential duration (APD) is maintained in KChIP2 knockout mice.

OBJECTIVE

We tested the role of KChIP2 in regulating APD and studied the underlying ionic currents.

METHODS

We used microelectrode techniques, whole-cell patch clamp studies, and real-time polymerase chain reaction amplification to characterize ventricular repolarization and its determinants in wild-type and KChIP2(-/-) mice.

RESULTS

Despite comparable baseline action potentials, APD was more markedly prolonged by 4-aminopyridine (4-AP) in KChIP2(-/-) preparations. Peak K(+) current densities were similar in wild-type and KChIP2(-/-) cells (mean +/- SEM I(P): 28.3 +/- 2 (n = 27) vs. 29.2 +/- 2 pA/pF (n = 24), respectively; P > .05). Heteropodatoxin-2 (HpTx-2, 1 microM) had no effect on current amplitude in KChIP2(-/-) myocytes. The current fractions sensitive to 4-AP (50 microM and 1 mM) were larger in KChIP2(-/-) than wild-type (P < .05). Real-time polymerase chain reaction showed absence of KChIP2 and increased K(V)1.5 expression in KChIP2(-/-) ventricular myocardium.

CONCLUSION

KChIP2 deficiency eliminated HpTx-2-sensitive I(to,f), but had little impact on total APD, secondary to upregulation of 4-AP-sensitive I(K,slow) in association with increased K(V)1.5 expression. There is increased sensitivity to 4-AP-mediated APD prolongation in KChIP2(-/-). Thus, KChIP2 seems important for murine repolarization in circumstances of reduced repolarization reserve.

The molecular genetics of arrhythmias and sudden death

The current status of the research in genetics of cardiac diseases causing sudden death is reviewed. Few techniques will impact medicine as will those of molecular biology. The identification of the gene-causing diseases will allow the use of better preventive, diagnostic, and therapeutic options. From genetic counseling at present to gene therapy in the future, the new challenge for the clinician will be to acquire the new information provided by molecular biology and apply it at the bedside to improve the quality of life for the patient.

Prevalence of long and short QT in a young population of 41,767 predominantly male Swiss conscripts

BACKGROUND

Abnormally long and short QT intervals are recognized to be associated with an increased risk for life-threatening ventricular arrhythmias. It is therefore important to define the upper and lower border of the normal QT.

OBJECTIVE

The aim of this study was to describe the normal distribution of the QT interval in a contemporary population of young conscripts and to define long and short limits of the QT interval.

METHODS

In Switzerland, all young male citizens must undergo compulsory conscription for the Swiss Army at the age of 18 to 19 years. In every conscript, an electrocardiogram (ECG) is performed. Retrospectively, 41,767 consecutive ECGs of Swiss citizens who underwent conscription for the army between March 1, 2004, and July 31, 2006, were analyzed.

RESULTS

The mean QTc Bazett interval was 394 +/- 22 ms. One percent of the conscripts had a Bazett QTc shorter than 347 ms, and one percent had a Bazett QTc longer than 445 ms, respectively. None of the subjects presented a QTc Bazett < 300 ms; the prevalence of a QTc Bazett < 320 ms was 0.02%.

CONCLUSION

The present study shows the distribution of QT intervals in an unselected young population. Because none of the subjects presented a QTc < 300 ms, it may be concluded that the short QT syndrome is a very rare entity in the population of young male adults.

High prevalence of four long QT syndrome founder mutations in the Finnish population

AIMS

Long QT syndrome (LQTS) is an inherited arrhythmia disorder with an estimated prevalence of 0.01%-0.05%. In Finland, four founder mutations constitute up to 70% of the known genetic spectrum of LQTS. In the present survey, we sought to estimate the actual prevalence of the founder mutations and to determine their effect sizes in the general Finnish population.

METHODS AND RESULTS

We genotyped 6334 subjects aged > or =30 years from a population cohort (Health 2000 study) for the four Finnish founder mutations using Sequenom MALDI-TOF mass spectrometry. The electrocardiogram (ECG) parameters were measured from digital 12-lead ECGs, and QT intervals were adjusted for age, sex, and heart rate using linear regression. A total of 27 individuals carried one of the founder mutations resulting in their collective prevalence estimate of 0.4% (95% CI 0.3%-0.6%). The KCNQ1 G589D mutation (n=8) was associated with a 50 ms (SE 7.0) prolongation of the adjusted QT interval (P=9.0x10(-13)). The KCNH2 R176W variant (n=16) resulted in a 22 ms (SE 4.7) longer adjusted QT interval (P=2.1x10(-6)).

CONCLUSION

In Finland 1 individual out of 250 carries a LQTS founder mutation, which is the highest documented prevalence of LQTS mutations that lead to a marked QT prolongation.

Long QT Syndrome

The hereditary Long QT syndrome (LQTS) is a genetic channelopathy with variable penetrance that is associated with increased propensity for polymorphic ventricular tachyarrhythmias and sudden cardiac death in young individuals with normal cardiac morphology. The diagnosis of this genetic disorder relies on a constellation of electrocardiographic, clinical, and genetic factors. Accumulating data from recent studies indicate that the clinical course of affected LQTS patients is time-dependent and age-specific, demonstrating important gender differences among age groups. Risk assessment should consider age-gender interactions, prior syncopal history, QT-interval duration, and genetic factors. Beta-blockers constitute the mainstay therapy for LQTS, while left cardiac sympathetic denervation and implantation of a cardioverter defibrillator should be considered in patients who remain symptomatic despite beta-blocker therapy. Current and ongoing studies are also evaluating genotype-specific therapies that may reduce the risk for life-threatening cardiac events in high-risk LQTS patients.

Neurophyisological and neurocognitive endophenotypes for schizophrenia genetics research

There is growing interest in the genetic analysis of schizophrenia using endophenotypes rather than clinical diagnosis or symptom dimensions. Endophenotypes could be alternative phenotypes for the clinical phenotypes. With their intermedicate and quantitative characteristics, endophenotypes could be functionally important links in the pathways between the genetic variation and clinical expression of the disorder. In this regard, the neurophysiological and neurocognitive endophenotypes used in the genetic analysis of schizophrenia have been reviewed.

Identification of a possible pathogenic link between congenital long QT syndrome and epilepsy

BACKGROUND

Long QT syndrome (LQTS) typically presents with syncope, seizures, or sudden death. Patients with LQTS have been misdiagnosed with a seizure disorder or epilepsy and treated with antiepileptic drug (AED) medication. The gene, KCNH2, responsible for type 2 LQTS (LQT2), was cloned originally from the hippocampus and encodes a potassium channel active in hippocampal astrocytes. We sought to test the hypothesis that a "seizure phenotype" was ascribed more commonly to patients with LQT2.

METHODS

Charts were reviewed for 343 consecutive, unrelated patients (232 females, average age at diagnosis 27 +/- 18 years, QTc 471 +/- 57 msec) clinically evaluated and genetically tested for LQTS from 1998 to 2006 at two large LQTS referral centers. A positive seizure phenotype was defined as the presence of either a personal or family history of seizures or history of AED therapy.

RESULTS

A seizure phenotype was recorded in 98/343 (29%) probands. A seizure phenotype was more common in LQT2 (36/77, 47%) than LQT1 (16/72, 22%, p < 0.002) and LQT3 (7/28, 25%, p < 0.05, NS). LQT1 and LQT3 combined cohorts did not differ significantly from expected, background rates of a seizure phenotype. A personal history of seizures was more common in LQT2 (30/77, 39%) than all other subtypes of LQTS (11/106, 10%, p < 0.001).

CONCLUSIONS

A diagnostic consideration of epilepsy and treatment with antiepileptic drug medications was more common in patients with LQT2. Like noncardiac organ phenotypes observed in other LQTS-susceptibility genes such as KCNQ1/deafness and SCN5A/gastrointestinal symptoms, this novel LQT2-epilepsy association raises the possibility that LQT2-causing perturbations in the KCNH2-encoded potassium channel may confer susceptibility for recurrent seizure activity.

Protective effect of KCNH2 single nucleotide polymorphism K897T in LQTS families and identification of novel KCNQ1 and KCNH2 mutations

BACKGROUND

KCNQ1 and KCNH2 are the two most common potassium channel genes causing long QT syndrome (LQTS), an inherited cardiac arrhythmia featured by QT prolongation and increased risks of developing torsade de pointes and sudden death. To investigate the disease expressivity, this study aimed to identify mutations and common variants that can modify LQTS phenotype.

METHODS

In this study, a cohort of 112 LQTS families were investigated. Among them two large LQTS families linkage analysis with markers spanning known LQTS genes was carried out to identify the specific gene for mutational analysis. All exons and exon-intron boundaries of KCNH2 and KCNQ1 were sequenced for mutational analysis.

RESULTS

LQTS-associated mutations were identified in eight of 112 families. Two novel mutations, L187P in KCNQ1 and 2020insAG in KCNH2, were identified. Furthermore, in another LQTS family we found that KCNH2 mutation A490T co-segregated with a common SNP K897T in KCNH2. KCNH2 SNP K897T was reported to exert a modifying effect on QTc, but it remains controversial whether it confers a risk or protective effect. Notably, we have found that SNP K897T interacts with mutation A490T in cis orientation. Seven carriers for A490T and the minor allele T of SNP K897T showed shorter QTc and fewer symptoms than carriers with A490T or A490P (P < 0.0001).

CONCLUSION

Our family-based approach provides support that KCNH2 SNP K897T confers a protective effect on LQTS patients. Our study is the first to investigate the effect of SNP K897T on another KCNH2 mutation located in cis orientation. Together, our results expand the mutational and clinical spectrum of LQTS and provide insights into the factors that determine QT prolongation associated with increased risk of ventricular tachycardia and sudden death.

Evidence for a heritable unidimensional symptom factor underlying obsessionality

The division of obsessive-compulsive symptoms (OCS) into specific factors is now widely accepted. However, the utility of these categories for genetic studies remains unclear, as studies examining their heritability have been inconsistent. Less attention has been paid to the possibility that clinically significant obsessionality is primarily determined by a "core" group of OCS that crosses the boundaries between symptom subgroups. The aim of this study is to determine whether such a core group exists, and to compare its heritability to that of the more traditionally derived symptom factors. We examined the properties and heritability of obsessive-compulsive symptoms in college students, medical students, and obsessive-compulsive disorder (OCD) families using the Leyton Obsessional Inventory. In each of the three samples, we identified a core group of symptoms that comprised a single unique construct and accounted for over 90% of the variation of the four more traditional symptom factors. This core construct was highly correlated with OCD in our families and had a heritability estimate of 0.19 when OCD was not included as a covariate and 0.49 when OCD was included as a covariate. In contrast, the four symptom factors were not heritable. There appears to be an underlying unidimensional component to obsessionality, both in non-clinical and clinical samples. This component, which is heritable, accounts for the majority of the variation of the more traditionally derived symptom factors in our sample, and is composed of OCS that are not specific to any of the symptom subgroups.

Sudden cardiac death in athletes

Sudden cardiac death in athletes is an uncommon but extremely visible event because of the high profile of amateur and professional athletes and the expected excellent health of these athletes. However, paradoxically, athletic performance may immediately increase the risk of ventricular arrhythmias and sudden cardiac death while run reducing atherosclerosis, which thus improves cardiovascular health and longevity. In athletes younger than 30 years, the most common underlying causes are due to inherited heart disease. In the older athletes, sudden death is generally due to arrhythmias in the context of coronary artery disease. Many athletes with aborted sudden death, arrhythmia-related syncope, or high-risk genetic disorders benefit from therapy with implanted cardioverter/defibrillators (ICDs) . Although ICD therapy can effectively abort sudden death, implantation of an ICD generally prohibits an individual from all competitive athletics except low-intensity sports. The screening of athletes has been notoriously inadequate; however, the optimal screening strategies have yet to be determined. Recommendations for participation in competitive athletics generally follow the recently published 36th Bethesda Conference Eligibility Recommendations for Competitive Athletes with Cardiovascular Abnormalities.

Congenital long QT syndrome

Congenital long QT syndrome (LQTS) is a hereditary cardiac disease characterized by a prolongation of the QT interval at basal ECG and by a high risk of life-threatening arrhythmias. Disease prevalence is estimated at close to 1 in 2,500 live births. The two cardinal manifestations of LQTS are syncopal episodes, that may lead to cardiac arrest and sudden cardiac death, and electrocardiographic abnormalities, including prolongation of the QT interval and T wave abnormalities. The genetic basis of the disease was identified in the mid-nineties and all the LQTS genes identified so far encode cardiac ion channel subunits or proteins involved in modulating ionic currents. Mutations in these genes (KCNQ1, KCNH2, KCNE1, KCNE2, CACNA1c, CAV3, SCN5A, SCN4B) cause the disease by prolonging the duration of the action potential. The most prevalent LQTS variant (LQT1) is caused by mutations in the KCNQ1 gene, with approximately half of the genotyped patients carrying KCNQ1 mutations. Given the characteristic features of LQTS, the typical cases present no diagnostic difficulties for physicians aware of the disease. However, borderline cases are more complex and require the evaluation of various electrocardiographic, clinical, and familial findings, as proposed in specific diagnostic criteria. Additionally, molecular screening is now part of the diagnostic process. Treatment should always begin with beta-blockers, unless there are valid contraindications. If the patient has one more syncope despite a full dose beta-blockade, left cardiac sympathetic denervation (LCSD) should be performed without hesitation and implantable cardioverter defibrillator (ICD) therapy should be considered with the final decision being based on the individual patient characteristics (age, sex, clinical history, genetic subgroup including mutation-specific features in some cases, presence of ECG signs - including 24-hour Holter recordings - indicating high electrical instability). The prognosis of the disease is usually good in patients that are correctly diagnosed and treated. However, there are a few exceptions: patients with Timothy syndrome, patients with Jervell Lange-Nielsen syndrome carrying KCNQ1 mutations and LQT3 patients with 2:1 atrio-ventricular block and very early occurrence of cardiac arrhythmias.

Long QT syndrome

The hereditary long QT syndrome (LQTS) is a genetic channelopathy with variable penetrance that is associated with increased propensity to syncope, polymorphous ventricular tachycardia (torsades de pointes), and sudden arrhythmic death. This inherited cardiac disorder constitutes an important cause of malignant ventricular arrhythmias and sudden cardiac death in young individuals with normal cardiac morphology. Risk assessment in affected LQTS patients relies upon a constellation of electrocardiographic, clinical, and genetic factors. Administration of beta-blockers is the mainstay therapy in affected patients, and primary prevention with an implantable cardioverter defibrillator or left cervicothoracic sympathetic denervation are therapeutic options in patients who remain symptomatic despite beta-blocker therapy. Accumulating data from the International LQTS Registry have recently facilitated a comprehensive analysis of risk factors for aborted cardiac arrest or sudden cardiac death in pre-specified age groups, including the childhood, adolescence, adulthood, and post-40 periods. These analyses have consistently indicated that the phenotypic expression of LQTS is time dependent and age specific, warranting continuous risk assessment in affected patients. Furthermore, the biophysical function, type, and location of the ion-channel mutation are currently emerging as important determinants of outcome in genotyped patients. These new data may be used to improve risk stratification and for the development of gene-specific therapies that may reduce the risk of life-threatening cardiac events in patients with this inherited cardiac disorder.

Identification of large gene deletions and duplications in KCNQ1 and KCNH2 in patients with long QT syndrome

BACKGROUND

Sequencing or denaturing high-performance liquid chromatography (dHPLC) analysis of the known genes associated with the long QT syndrome (LQTS) fails to identify mutations in approximately 25% of subjects with inherited LQTS. Large gene deletions and duplications can be missed with these methodologies.

OBJECTIVE

The purpose of this study was to determine whether deletions and/or duplications of one or more exons of the main LQTS genes were present in an LQTS mutation-negative cohort.

METHODS

Multiplex ligation-dependent probe amplification (MLPA), a quantitative fluorescent approach, was used to screen 26 mutation-negative probands with an unequivocal LQTS phenotype (Schwartz score >4). The appropriate MLPA kit contained probes for selected exons in LQTS genes KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2. Real-time polymerase chain reaction was used to validate the MLPA findings.

RESULTS

Altered exon copy number was detected in 3 (11.5%) patients: (1) an ex13-14del of the KCNQ1 gene in an 11-year-old boy with exercise-induced collapse (QTc 580 ms); (2) an ex6-14del of the KCNH2 gene in a 22-year-old woman misdiagnosed with epilepsy since age 9 years (QTc 560 ms) and a sibling with sudden death at age 13 years; and (3) an ex9-14dup of the KCNH2 gene in a 12 year-old boy (QTc 550 ms) following sudden nocturnal death of his 32-year-old mother.

CONCLUSION

If replicated, this study demonstrates that more than 10% of patients with LQTS and a negative current generation genetic test have large gene deletions or duplications among the major known LQTS susceptibility genes. As such, these findings suggest that sequencing-based mutation detection strategies should be followed by deletion/duplication screening in all LQTS mutation-negative patients.

Risk of death in the long QT syndrome when a sibling has died

BACKGROUND

Sudden death of a sibling is thought to be associated with greater risk of death in long QT syndrome (LQTS). However, there is no evidence of such an association.

OBJECTIVE

This study sought to test the hypothesis that sudden death of a sibling is a risk factor for death or aborted cardiac arrest (ACA) in patients with LQTS.

METHODS

We examined all probands and first-degree and second-degree relatives in the International Long QT Registry from birth to age 40 years with QTc >/= 0.45 s. Covariates included sibling death, QTc, gender by age, syncope, and implantable cardioverter-defibrillator (ICD) and beta-blocker treatment. End points were (1) severe events (ACA, LQTS-related death) and (2) any cardiac event (syncope, ACA, or LQTS-related death).

RESULTS

Of 1915 subjects, 270 had a sibling who died. There were 213 severe events and 829 total cardiac events. More subjects with history of sibling death received beta-blocker therapy. Sibling death was not significantly associated with risk of ACA or LQTS-related death, but was associated with increased risk of syncope. QTc >/= 0.53 s (hazard ratio 2.5, P <.01), history of syncope (hazard ratio 6.1, P <.01), and gender were strongly associated with risk of ACA or LQTS-related death.

CONCLUSION

Sudden death of a sibling prompted more aggressive treatment but did not predict risk of death or ACA, whereas QTc >/= 0.53 s, gender, and syncope predicted this risk. All subjects should receive appropriate beta-blocker therapy. The decision to implant an ICD should be based on an individual's own risk characteristics (QTc, gender, and history of syncope).

Long-QT Syndrome After Age 40

Background— Previous studies that assessed the risk of life-threatening cardiac events in patients with congenital long-QT syndrome (LQTS) have focused mainly on the first 4 decades of life, whereas the clinical course of this inherited cardiac disorder in the older population has not been studied.

Methods and Results— The risk of aborted cardiac arrest or death from age 41 though 75 years was assessed in 2759 subjects from the International LQTS Registry, categorized into electrocardiographically affected (corrected QT interval [QTc] ≥470 ms), borderline (QTc 440 to 469 ms), and unaffected (QTc <440 ms) subgroups. The affected versus unaffected adjusted hazard ratio for aborted cardiac arrest or death was 2.65 ( P <0.001) in the age range of 41 to 60 years and 1.23 ( P =0.31) in the age range of 61 to 75 years. The clinical course of study subjects displayed gender differences: Affected LQTS women experienced a significantly higher cumulative event rate (26%) than borderline (16%) and unaffected (12%) women ( P =0.001), whereas event rates were similar among the 3 respective subgroups of men (29%, 26%, and 27%; P =0.16). Recent syncope (<2 years in the past) was the predominant risk factor in affected subjects (hazard ratio 9.92, P <0.001), and the LQT3 genotype was identified as the most powerful predictor of outcome in a subset of 871 study subjects who were genetically tested for a known LQTS mutation (hazard ratio 4.76, P =0.02).

Conclusions— LQTS subjects maintain a high risk for life-threatening cardiac events after age 40 years. The phenotypic expression of affected subjects is influenced by age-specific factors related to gender, clinical history, and the LQTS genotype.

Risk factors for aborted cardiac arrest and sudden cardiac death in children with the congenital long-QT syndrome

BACKGROUND

The congenital long-QT syndrome (LQTS) is an important cause of sudden cardiac death in children without structural heart disease. However, specific risk factors for life-threatening cardiac events in children with this genetic disorder have not been identified.

METHODS AND RESULTS

Cox proportional-hazards regression modeling was used to identify risk factors for aborted cardiac arrest or sudden cardiac death in 3015 LQTS children from the International LQTS Registry who were followed up from 1 through 12 years of age. The cumulative probability of the combined end point was significantly higher in boys (5%) than in girls (1%; P<0.001). Risk factors for cardiac arrest or sudden cardiac death during childhood included corrected QT interval [QTc] duration > 500 ms (hazard ratio [HR]; 2.72; 95% confidence interval [CI], 1.50 to 4.92; P=0.001) and prior syncope (recent syncope [< 2 years]: HR, 6.16; 95% CI 3.41 to 11.15; P<0.001; remote syncope [> or = 2 years]: HR, 2.67; 95% CI, 1.22 to 5.85; P=0.01) in boys, whereas prior syncope was the only significant risk factor among girls (recent syncope: HR, 27.82; 95% CI, 9.72 to 79.60; P<0.001; remote syncope: HR, 12.04; 95% CI, 3.79 to 38.26; P<0.001). Beta-blocker therapy was associated with a significant 53% reduction in the risk of cardiac arrest or sudden cardiac death (P=0.01).

CONCLUSIONS

LQTS boys experience a significantly higher rate of fatal or near-fatal cardiac events than girls during childhood. A QTc duration > 500 ms and a history of prior syncope identify risk in boys, whereas prior syncope is the only significant risk factor among girls. Beta-blocker therapy is associated with a significant reduction in the risk of life-threatening cardiac events during childhood.

Long QT syndrome: A therapeutic challenge

Congenital long QT syndrome (LQTS) is one of the most common cardiac channelopathies and is characterized by prolonged ventricular repolarization and life-threatening arrhythmias. The mortality is high among untreated patients. The identification of several LQTS genes has had a major impact on the management strategy for both patients and family members. An impressive genotype-phenotype correlation has been noted and genotype identification has enabled genotype specific therapies. Beta blockers continue to be the primary treatment for prevention of life threatening arrhythmias in the majority of patients. Other therapeutic options include pacemakers, implantable cardioverter defibrillators, left cardiac sympathetic denervation, sodium channel blocking medications and lifestyle modification.

Challenges of Diagnosis of Long-QT Syndrome in Children

We describe the clinical and genetic characteristics of the family, in which the diagnosis of LQT1 had been made. The electrocardiogram (ECG) characteristics of this patient indicated the likelihood of LQTS1. Polymorphic ventricular extrasystolies and episodes of polymorphic non-sustained ventricular tachycardia were confirmed by Holter ECG monitoring. On the exertional electrocardiogram polymorphic ventricular tachycardia (torsade de pointes) was recorded. Direct sequencing of both DNA strands revealed the absence of mutations or polymorphisms in the KCNQ1, HERG, and SCN5A genes.

The Shortage of Short QT Intervals

BACKGROUND

Syncope or sudden death has been associated with a short QT interval (QTc, < 300 ms), the so-called short QT syndrome. The current prevalence of this syndrome is unknown. The aim of this study was to evaluate the prevalence of short QT intervals (ie, QTc, < 300 ms) in a general hospital population.

METHODS

We retrospectively queried 479,120 consecutive ECGs that had been archived (Marquette MAC 5000 Resting ECG System; GE Healthcare; Boston, MA) over a 16-year period. We examined the distribution of QT intervals in our population from 150 randomly selected ECGs with normal findings, excluding patients who had been receiving medications known to prolong the QT interval.

RESULTS

From 1988 to 2004, 479,120 ECGs from 106,432 patients were analyzed, which reported 215 tracings with a QTc of < 300 ms. Each ECG was then measured manually, and no QTc of < 300 ms was validated (67% were found to be in error because of a pacemaker artifact, 17% showed supraventricular tachycardia with inaccurate detection of the T-wave offset, and 16% were found to have an error in the cycle length calculation). Therefore, not one of the 106,432 patients was found to have a QTc of < 300 ms. The mean QTc (+/- SD) was 430 +/- 19 ms (95% confidence interval, 392 to 468 ms). The QTc of < 300 ms would then reflect > 5 SDs shorter than the mean QTc.

CONCLUSIONS

The short QTc reported by an ECG computer was inaccurate and required manual correction. Short QT syndrome, defined as a QTc of < or = 300 ms, is rare. We were unable to find one patient among a population > 100,000 patients with a true QTc of < 300 ms.

The electrocardiogram in the patient with syncope

Syncope is a common and challenging presentation for the emergency physician. Various investigators have developed clinical risk score and clinical decision rules which are designed to identify the population at highest risk for adverse events. In each of these clinical decision tools, the electrocardiogram (ECG) is one of the key clinical variables used to evaluate the patient. Certain electrocardiographic presentations in the patient with syncope will not only provide a reason for the loss of consciousness but also guide early therapy and disposition in this individual. Bradycardia, atrioventricular block, intraventricular conduction abnormality, and tachydysrhythmia in the appropriate clinical setting provide an answer to the clinician for the syncopal event. Morphologic findings suggesting the range of cardiovascular malady are also encountered; these entities are far ranging, including the various ST-segment and T-wave abnormalities of acute coronary syndrome, ventricular preexcitation as seen in the Wolff-Parkinson-White syndrome, Brugada syndrome with the associated tendency for sudden death, prolonged QT interval common in the diverse long QT interval presentations, and right ventricular hypertrophy suggestive of hypertrophic cardiomyopathy. This review discusses the ECG in the patient with syncope. The general use of the 12-lead ECG in this patient population is discussed. Furthermore, specific electrocardiographic presentations seen in the patient with syncope are also reviewed.

Further evidence of inherited long QT syndrome gene mutations in antiarrhythmic drug-associated torsades de pointes

BACKGROUND

Pathophysiologically significant ion-channel mutations have been detected in only a minority of cases of acquired long QT syndrome (LQTS).

OBJECTIVE

The aim of this study was to clarify the putative role of subclinical inherited LQTS in drug-associated torsades de pointes (TdP) and to assess the concomitant proarrhythmic factors.

METHODS

We evaluated 16 consecutive cases with documented, antiarrhythmic drug-induced TdP who were referred to the Laboratory of Molecular Medicine at Helsinki University for LQTS genetic testing between September 2000 and August 2005.

RESULTS

A prolonged QTc interval was observed in 56% of the patients before administration of the drug. TdP was associated with amiodarone in seven, sotalol in six, flecainide in two, and propafenone in one of the cases. Except for the culprit drug, one or more risk factors such as female sex, congestive heart failure, and atrial fibrillation were present in each drug-associated TdP. DNA samples were screened for the four common Finnish founder mutations (KCNQ1 G589D and IVS7-2A-->G, HERG L552S, and R176W), which are known to account for the majority of inherited LQTS in Finland. A total of three (19%) individuals carried one of these four mutations.

CONCLUSIONS

Our data show that previously unsuspected LQTS mutations may be present in patients with antiarrhythmic drug-associated TdPs. A normal QTc interval does not exclude the risk of proarrhythmia.

Long QT syndrome in adults

OBJECTIVES

The aims of this study were: 1) to evaluate risk factors influencing the clinical course of mutation-confirmed adult patients with long QT syndrome (LQTS), 2) to study life-threatening cardiac events as a specific end point in adults, and 3) to examine the protective effect of beta-blocker therapy on cardiac events in adult LQTS patients with known cardiac channel mutations.

BACKGROUND

The clinical course and risk factors for cardiac events in genotype-confirmed adult patients with LQTS have not been previously investigated.

METHODS

The clinical characteristics of 812 mutation-confirmed LQTS patients age 18 years or older were studied with both univariate and multivariate analyses to determine the genotype-phenotype factors that influence the clinical course of adult patients with this disorder.

RESULTS

Female gender, corrected QT (QTc) interval, LQT2 genotype, and frequency of cardiac events before age 18 years were associated with increased risk of having any cardiac events between the ages of 18 and 40 years. Female gender, QTc interval > or =500 ms, and interim syncopal events during follow-up after age 18 years were associated with significantly increased risk of life-threatening cardiac events in adulthood. Beta-blockers provided a 60% reduction in risk of any cardiac event and life-threatening events, with somewhat greater effect in higher-risk subjects.

CONCLUSIONS

The severity of LQTS in adulthood can be risk stratified with information regarding genotype, gender, QTc duration, and history of cardiac events. Beta-blockers effectively reduce but do not eliminate the risk of both syncopal and life-threatening cardiac events in adult patients with mutation-confirmed LQTS.

Repolarization morphology in adult LQT2 carriers with borderline prolonged QTc interval

BACKGROUND

At least 50% of LQT2 carriers have borderline QTc (0.42-0.47 s), and they present a diagnostic difficulty to clinicians evaluating patients suspected of having long QT syndrome (LQTS).

OBJECTIVES

Because QTc in this borderline range is nondiagnostic, the purpose of this study was to investigate whether analysis of phenotypic features of T-wave morphology could help identify LQT2 carriers with normal or near-normal QTc-interval duration.

METHODS

Standard 12-lead ECGs recorded without beta-blockers from LQT2 carriers (n = 90, 33 +/- 14 years, 61% female) and noncarriers (n = 69, 38 +/- 17 years, 58% female) were digitized. The following parameters were automatically measured: RR interval, QT/QTc, QT apex, T-wave amplitude, ascending (alpha(L)) and descending slopes (alpha(R)) of the T wave, and T-wave symmetry. We used a linear logistic regression model to identify the most relevant parameters for separating LQT2 carriers from noncarriers, within the overall population and among patients without overt QTc prolongation (390 </= QTc </= 470).

RESULTS

Logistic regression selected three parameters: QT, RR interval, and alpha(L) in all models. In the overall population, the model provided 92.7% sensitivity and 90.0% specificity. In the group of patients without beta-blockers and near-normal QTc interval, 92.0% sensitivity (n = 46) and 81.4% specificity (n = 49) were achieved by the model including alpha(L.)

CONCLUSION

Abnormal T-wave morphology is a phenotypic expression of LQT2, and its quantification could be used to identify patients with suspected LQTS who do not have overt QTc prolongation (QTc >470).

Electrocardiographic markers of sudden death

The 12-lead ECG has limited utility to predict the risk for sudden cardiac death in common cardiac diseases such as coronary artery disease and idiopathic dilated cardiomyopathy. However, it is quite useful in diagnosing less common cardiac conditions that are associated with an increased risk for sudden death.

Can pharmacogenetics help rescue drugs withdrawn from the market?

Observations over the later half of the last century have suggested that genetic factors may be the prime determinant of drug response, at least for some drugs. Retrospectively gathered data have provided further support to the notion that genotype-based prescribing will improve the overall efficacy rates and minimize adverse drug reactions (ADRs), making personalized medicine a reality. During the last 16 years, 38 drugs have been withdrawn from major markets due to safety concerns. Inevitably, a question arises as to whether it might be possible to 'rescue' some of these drugs by promoting genotype-based prescribing. However, ironically pharmacogenetics has not perceptibly improved the risk/benefit of a large number of genetically susceptible drugs that are already in wide clinical use and are associated with serious ADRs. Drug-induced hepatotoxicity and QT interval prolongation (with or without torsade de pointes) account for 24 (63%) of these 38 drug withdrawals. In terms of the number of drugs implicated, both these toxicities are on the increase. Many others have had to be withdrawn due to their inappropriate use. This paper discusses the criteria that a drug would need to fulfill, and summarizes the likely regulatory requirements, before its pharmacogenetic rescue can be considered to be realistic. One drug that fulfils these criteria is perhexiline (withdrawn worldwide in 1988) and is discussed in some detail. For the majority of these 38 drugs there are, at present, no candidates for genetic traits to which the toxicity that led to their withdrawal may be linked. For a few other drugs where a potential candidate for a genetic trait might explain the toxicity of concern, the majority of patients who experienced the index toxicity had easily managed nongenetic risk factors. It may be possible to rescue these drugs simply by careful attention to their dose, interaction potential and prescribing patterns, but without the need for any pharmacogenetic test. In addition, the pharmacogenetic rescue of drugs might not be as effective as anticipated as hardly any pharmacogenetic test is known to have the required test efficiency to promote individualized therapy. Multiple pathways of drug elimination, contribution to toxicity by metabolites as well as the parent drug, gene-gene interactions, multiple mechanisms of toxicity and inadequate characterization of phenotype account for this lack of highly predictive tests. The clinical use of tests that lack the required efficiency carries the risks of over- or under-dosing some patients, denying the drug to others and decreasing physician vigilance of patients. Above all, at present, prescribing physicians lack an adequate understanding of pharmacogenetics and its limitations. It is also questionable whether their prescribing will comply with the requirements for pretreatment pharmacogenetic tests to make pharmacogenetic rescue a realistic goal.

Variable expression of long QT syndrome among gene carriers from families with five different HERG mutations

OBJECTIVES

This study assessed the phenotypic variability of LQTS in carriers with the same and with different mutations in the LQT2 gene.

BACKGROUND

Mutations of ion-channel genes are known to cause the long QT syndrome (LQTS), a disorder associated with distinctive genotypic-specific electrocardiographic patterns and variable clinical expression.

METHODS

Clinical and electrocardiographic characteristics were assessed in five large LQTS families, each with a different mutation of the HERG gene (LQT2; n = 469, 69% genotyped, 102 carriers). One mutation was located on the N-terminus and the other four on the C-terminus of the HERG channel protein.

RESULTS

The QTc duration and the frequency of cardiac events (syncope and LQTS-related cardiac arrest/death) were similar among carriers with the five HERG mutations. QTc was as variable in carriers of the same mutation as it was among carriers with different HERG mutations (P = 0.19). Qualitative assessment of the electrocardiograms revealed extensive intra-and interfamilial variability in T-wave morphology. Among carriers with multiple electrocardiograms extending over 2 to 7 years, variation in QTc over time was minimal. A strong association was found between QTc and the occurrence of cardiac events in carriers of all five mutations.

CONCLUSIONS

The clinical expression of LQTS was equally variable in carriers from families with the same or different HERG mutations. These findings highlight the complexity of the clinical phenotype in this Mendelian dominant disorder and suggest that one or more modifier genes contribute to the variable expression of this syndrome.

Epinephrine QT stress testing in congenital long QT syndrome

Epinephrine QT stress testing is an effective diagnostic tool to unmask concealed Long QT Syndrome (LQTS), particularly type 1 LQTS (LQT1). Unique responses have also been observed in patients with LQT2 and LQT3, making this test invaluable in the diagnostic work-up of LQTS. This article reviews the epinephrine QT stress test, explains the pathological basis of differential responses among patients and healthy individuals, and describes the methodology for conducting the test and the interpretation of the responses. We have also attempted to highlight the differences between the two major LQTS epinephrine QT stress test protocols, the Mayo protocol and the Shimizu protocol.

Advances in congenital long QT syndrome

PURPOSE OF REVIEW

Dramatic advances have been made in understanding of both the genetics and the phenotypic expression of congenital long QT syndrome. This paper reviews recent clinically relevant literature.

RECENT FINDINGS

Long QT syndrome is one of the leading causes of sudden cardiac death. This syndrome, once diagnosed by a clinical profile, has been more clearly defined by specific gene defects causing ion channel abnormalities in the beating heart. Genetic testing for long QT syndrome, once available only through research laboratories, is now commercially available. Diagnosis, risk assessment, and management are increasingly being guided by gene-specific diagnoses. In a family with suspected disease, the genetic test will determine the defect in as many as 75% of subjects. Once the diagnosis is made, the mainstay of therapy continues to be beta-blockers. Implantable cardioverter-defibrillators are indicated in patients at high risk for malignant arrhythmias.

SUMMARY

Long QT syndrome is one of the first cardiovascular diseases to see the dramatic changes that bench research can bring to the clinical arena. Future research is needed to determine the gene defect in the remaining 25% of patients with suspected long QT syndrome and in risk stratification.

Clinical course and risk stratification of patients affected with the Jervell and Lange-Nielsen syndrome

INTRODUCTION

Data regarding risk factors and clinical course of patients affected with Jervell and Lange-Nielsen syndrome (JLNS), an autosomal recessive form of the congenital long-QT syndrome (LQTS), are limited to several reported cases and a retrospective analysis.

METHODS AND RESULTS

We prospectively followed-up 44 JLNS patients from the U.S. portion of the International LQTS Registry and compared their clinical course with 2,174 patients with the phenotypically determined dominant form of LQTS (Romano-Ward syndrome [RWS]) and a subgroup of 285 patients with type 1 LQTS (LQT1). Mean (+/-SD) corrected QT interval (QTc) in the JLNS, RWS, and LQT1 groups were 548 +/- 73, 500 +/- 48, and 502 +/- 46 msec, respectively (P < 0.001). The cumulative rates of cardiac events from birth through age 40 among JLNS and RWS patients were 93% (mean [+/-SD] age: 5.0 +/- 7.0 years) and 54% (mean [+/-SD] age: 14.2 +/- 9.3 years), respectively (P < 0.001). The JLNS:RWS and JLNS:LQT1 adjusted hazard ratios (HR) for cardiac events were highest among patients with a baseline QTc > or = 550 msec (HR = 15.83 [P < 0.001] and 13.80 [P < 0.001], respectively). Among JLNS patients treated with beta-blockers, the cumulative probability of LQTS-related death was 35%; defibrillator therapy was associated with a 0% mortality rate during a mean (+/-SD) follow-up period of 4.9 +/- 3.4 years.

CONCLUSIONS

Patients with JLNS experience a high rate of cardiac and fatal events from early childhood despite medical therapy. Defibrillator therapy appears to improve outcome in this high-risk population, although longer follow-up is needed to establish its long-term efficacy.

Congenital long QT syndromes: clinical features, molecular genetics and genetic testing

Congenital long QT syndrome (LQTS) is a primary electrical disease characterized by a prolonged QT interval in the surface electrocardiogram and increased predisposition to a typical polymorphic ventricular tachycardia, termed Torsade de Pointes. Most patients with LQTS are asymptomatic and are diagnosed incidentally based on an electrocardiogram. Symptomatic patients may suffer from severe cardiac events, such as syncope and/or sudden cardiac death. Autosomal dominant forms are caused by heterozygous mutations in genes encoding the components of the ion channels. The autosomal recessive form with congenital deafness is also known as Jervell and Lang-Nielsen syndrome. It is caused by homozygous mutations or certain compound heterozygous mutations. Depending on the genetic defects, there are differences in the age of onset, severity of symptoms, and number of cardiac events and event triggers. With advances in gene technology, it is now feasible to perform genetic testing for LQTS, especially for those with family history. Identification of the mutation will lead to better management of symptoms and more targeted treatment, depending on the underlying genetic defect, resulting in a reduction of mortality and cardiac events.

Corrected QT variability in serial electrocardiograms in long QT syndrome: the importance of the maximum corrected QT for risk stratification

OBJECTIVES

We evaluated the incremental prognostic information provided by multiple corrected QT (QTc) measurements on serial electrocardiograms (ECGs) in patients with the inherited long QT syndrome (LQTS).

BACKGROUND

A baseline QTc of > or =500 ms has been shown to be associated with increased risk of cardiac events among LQTS patients. However, the value of QTc measurements on follow-up ECGs in risk assessment has not been determined.

METHODS

The risk of a first LQTS-related cardiac event during adolescence was assessed in 375 patients enrolled in the International LQTS Registry for whom serial follow-up ECGs were recorded before age 10.

RESULTS

The mean +/- SD difference between the minimum and maximum QTc values on serial ECGs recorded in study patients was 47 +/- 40 ms. The maximum QTc interval recorded before age 10 was the strongest predictor of cardiac events during adolescence (adjusted hazard ratio [HR] = 2.74; p < 0.001). Other follow-up QTc measures, including the baseline, the mean, and the most recent QTc interval recorded before age 10, were less significant risk factors. After adjusting for the maximum QTc value during follow-up, no significant association remained between the baseline QTc value and the risk of subsequent cardiac events (HR = 1.04; p = 0.91).

CONCLUSIONS

In LQTS patients, there is a considerable variability in QTc measures in serial follow-up ECGs. The maximum QTc interval provides incremental prognostic information beyond the baseline measurement. We suggest that risk stratification in LQTS patients should include follow-up ECG data.

The heterogeneous spectrum of the long QT syndrome

The long QT syndrome affects predominantly younger people who demonstrate structurally normal hearts. The underlying defect in the long QT syndrome seems to be genetic mutations in the cardiac ionic channels responsible for generating action potentials. Genetic linkage mapping has identified six genes (designated LQT1-6) associated with the Romano-Ward syndrome; two of these genes (LQT1, LQT5) are associated with the Jervell and Lange-Nielsen syndrome. All of these genes encode potassium channels with the exception of LQT3, which encodes a sodium channel. Mutations affecting these channels will lead to a derangement in ionic flows across the cytoplasmic membranes of cardiac cells, thereby leading to prolongation of the cardiac action potential and lengthening of the QT interval on the surface electrocardiogram. Long QT syndrome is a cause of death in young, otherwise healthy individuals. The heterogeneity of the long QT syndrome also makes prognosis and risk stratification difficult. In patients with long QT syndrome genotypes 1 and 2, as well as during slower heart rates, men exhibited shorter mean QTc interval durations than did women; thus, women possess a predilection for developing torsades de pointes. In female probands with the congenital long QT syndrome, the postpartum period appears to confer a significant risk for experiencing a cardiac event. The study determined that certain combinations, such as exhibiting a QTc of 500ms or more, along with the presence of LQT1, LQT2, and LQT3 (with male gender), conferred a 50% or greater risk of a first cardiac event. Based on the observation that physical exertion and emotional stress are significant triggers for cardiac events in the setting of congenital long QT syndrome (specifically the LQT1 and LQT2 genotypes), avoidance of competitive sports seems to be a prudent lifestyle modification. This heterogeneity stems from the presence of different mutations in the genes that encode cardiac ion channels. The triggering events, prognosis, and risk stratification of the patient with long QT syndrome appear to be influenced by the underlying genotype. The primary treatment of congenital long QT syndrome, i.e., beta-blockade therapy with internal cardioverter defibrillator therapy, appears to be useful in a subset of patients.

Sudden cardiac death without structural heart disease: update on the long QT and Brugada syndromes

The long QT syndrome (LQTS) and the Brugada syndrome (BrS) are the most common genetic causes of malignant ventricular arrhythmias and sudden cardiac death in young patients with normal cardiac morphology. To date, more than 250 different mutations in seven genes have been identified as causing LQTS, whereas the only gene identified to be linked to BrS is SCN5A. In both syndromes, gene-specific mutations have been shown to be associated with specific phenotypic expressions. Risk stratification in LQTS and BrS is based mainly upon a constellation of electrocardiographic findings and a history of prior symptoms. In patients identified as high risk for arrhythmic mortality, the implantable cardioverter defibrillator is the most effective treatment and has been shown to provide near-complete protection during long-term follow-up.

The Congenital Long QT Syndrome and Implications for Young Athletes

The congenital long QT syndrome (LQTS) is caused by cardiac ion channel mutations, which predispose young individuals to sudden cardiac death often related to exercise. The issue of LQTS and sports participation has received significant publicity due to reports of sudden death in young competitive athletes. This article reviews the pathophysiology, clinical characteristics, and management of LQTS in the physically active and athletic population.

The role of molecular autopsy in unexplained sudden cardiac death

PURPOSE OF REVIEW

Sudden cardiac death (SCD) is one of the most common causes of death, with many attributable to cardiac/coronary abnormalities evident at autopsy. A significant number of SCDs, however, particularly in young people, remain unexplained following a medico-legal investigation, including autopsy, and are referred to as autopsy-negative sudden unexplained death (SUD). Due to molecular advances, however, a cardiac channel molecular autopsy may potentially provide a pathogenic basis for SUD and establish cause and manner of death.

RECENT FINDINGS

Over the past decade, five population-based investigations of sudden death in young people elucidated the frequency of and causes responsible for these tragic events. The most inclusive epidemiologic study concluded that nearly 30% of SCDs in young people are autopsy-negative (i.e. SUD) and most likely secondary to cardiac channelopathies. Case reports on the post-mortem molecular diagnosis of cardiac channelopathies through the use of a molecular autopsy have been presented. Recently, a molecular autopsy series of SUD identified pathogenic mutations in long QT syndrome and catecholaminergic polymorphic ventricular tachycardia-associated genes in over one-third of cases. Similar post-mortem cardiac channel genetic testing in a large population-based cohort of sudden infant death syndrome has elucidated mutations in 5-10% of cases.

SUMMARY

With autopsy-negative SUD accounting for a significant number of sudden deaths in young people, a new role for the medical examiner is emerging. An accurate diagnosis, derived from a molecular autopsy, will guide the appropriate initiation of pre-emptive strategies in hopes of preventing future tragedies among those left behind.