Prolonged QT interval in hypertrophic and dilated cardiomyopathy in children

Dual effect of cardiac FKBP12.6 overexpression on excitation-contraction coupling and the incidence of ventricular arrhythmia depending on its expression level

FKBP12.6, a binding protein to the immunosuppressant FK506, which also binds the ryanodine receptor (RyR2) in the heart, has been proposed to regulate RyR2 function and to have antiarrhythmic properties. However, the level of FKBP12.6 expression in normal hearts remains elusive and some controversies still persist regarding its effects, both in basal conditions and during β-adrenergic stimulation. We quantified FKBP12.6 in the left ventricles (LV) of WT (wild-type) mice and in two novel transgenic models expressing distinct levels of FKBP12.6, using a custom-made specific anti-FKBP12.6 antibody and a recombinant protein. FKBP12.6 level in WT LV was very low (0.16 ± 0.02 nmol/g of LV), indicating that <15% RyR2 monomers are bound to the protein. Mice with 14.1 ± 0.2 nmol of FKBP12.6 per g of LV (TG1) had mild cardiac hypertrophy and normal function and were protected against epinephrine/caffeine-evoked arrhythmias. The ventricular myocytes showed higher [Ca2+]i transient amplitudes than WT myocytes and normal SR-Ca2+ load, while fewer myocytes showed Ca2+ sparks. TG1 cardiomyocytes responded to 50 nM Isoproterenol increasing these [Ca2+]i parameters and producing RyR2-Ser2808 phosphorylation. Mice with more than twice the TG1 FKBP12.6 value (TG2) showed marked cardiac hypertrophy with calcineurin activation and more arrhythmias than WT mice during β-adrenergic stimulation, challenging the protective potential of high FKBP12.6. RyR2R420Q CPVT mice overexpressing FKBP12.6 showed fewer proarrhythmic events and decreased incidence and duration of stress-induced bidirectional ventricular tachycardia. Our study, therefore, quantifies for the first time endogenous FKBP12.6 in the mouse heart, questioning its physiological relevance, at least at rest due its low level. By contrast, our work demonstrates that with caution FKBP12.6 remains an interesting target for the development of new antiarrhythmic therapies.

Effect of aqueous extract of Indigofera tinctoria (Linn) on aging-induced inflammation and its associated left ventricular hypertrophy and fibrosis in the rat

The aim of the present study is to investigate the ameliorative potential of the aqueous extract of Indigofera tinctoria (IT) in aging-induced inflammation and its associated cardiac hypertrophy and fibrosis. Young (3-month-old) and aged (24-26-month-old) male Wistar albino rats were grouped into young control, aged control, aged + IT, and young + IT. The animals in the supplementary groups received 200 mg/kg BWT of aqueous extract of IT orally once a day for 21 days. Aged animals showed prolonged QT interval and increased weight and volume of the heart with a thickening ventricular wall. Infiltration of leukocytes and increased cardiomyocyte diameter and decreased numerical density along with cardiomyocyte apoptosis and increased collagen accumulation were also seen in aged myocardium when compared to the young. The expression profile of various pro-inflammatory cytokines such as IL-6, IL-1β, TNF-α, NFκB, and iNOS was increased with a concomitant reduction in IL-10 expression in the aged compared to the young. In addition, a marked increase in ROS generation, TGF-β, and α-SMA levels is evident in the aged myocardium. These pathological changes were greatly reversed in aged animals supplemented with IT. Furthermore, the aged + IT group showed repression of pro-inflammatory markers with a subsequent increase in IL-10 expression. Contrarily, no marked changes were observed between young and young + IT groups. Taken together, it is concluded that the aqueous extract of Indigofera tinctoria suppresses cardiac fibrosis and hypertrophy by repressing the inflammation and its associated activation of TGFβ and myofibroblast conversion.

Cardiomyopathies in Children and Systemic Disorders When Is It Useful to Look beyond the Heart?

Cardiomyopathy (CMP) is a rare disease in the pediatric population, with a high risk of morbidity and mortality. The genetic etiology of CMPs in children is extremely heterogenous. These two factors play a major role in the difficulties of establishing standard diagnostic and therapeutic protocols. Isolated CMP in children is a frequent finding, mainly caused by sarcomeric gene variants with a detection rate that can reach up to 50% of analyzed cohorts. Complex multisystemic forms of pediatric CMP are even more heterogenous. Few studies in literature take into consideration this topic as the main core since it represents a rarity (systemic CMP) within a rarity (pediatric population CMP). Identifying etiology in this cohort is essential for understanding prognosis, risk stratification, eligibility to heart transplantation and/or mechanical-assisted procedures, preventing multiorgan complications, and relatives' recurrence risk calculation. The previous points represent a cornerstone in patients' empowerment and personalized medical care approach. The aim of this work is to propose a new approach for an algorithm in the setting of the diagnostic framework of systemic pediatric CMP. On the other hand, during the literature review, we noticed a relatively common etiologic pattern in some forms of complex/multisystem CMP. In other words, certain syndromes such as Danon, Vici, Alström, Barth, and Myhre syndrome share a common pathway of directly or indirectly defective "autophagy" process, which appears to be a possible initiating/triggering factor for CMPs. This conjoint aspect could be important for possible prognostic/therapeutic implications in this category of patients. However, multicentric studies detailed functional and experimental models are needed prior to deriving conclusions.

Markedly prolonged QTc interval in end-stage liver disease and risk of 30-day cardiovascular event after liver transplant

BACKGROUND AND AIM

The proportional increase of corrected QT interval (QTc) along end-stage liver disease (ESLD) severity may lead to inconsistent outcome reporting if based on conventional threshold of prolonged QTc. We investigated the comprehensive QTc distribution among ESLD patients and assessed the association between QTc > 500 ms, a criterion for diagnosing severe long-QT syndrome, and the 30-day major adverse cardiovascular event (MACE) after liver transplantation (LT) and identified the risk factors for developing QTc > 500 ms.

METHODS

Data were collected prospectively from the Asan LT Registry between 2011 and 2018, and outcomes were retrospectively reviewed. Multivariable analysis and propensity score-weighted adjusted odds ratios (ORs) were calculated. Thirty-day MACEs were defined as the composite of cardiovascular mortality, arrhythmias, myocardial infarction, pulmonary thromboembolism, and/or stroke.

RESULTS

Of 2579 patients, 194 (7.5%) had QTc > 500 ms (QTc500_Group), and 1105 (42.8%) had prolonged QTc (QTcP_Group), defined as QTc > 470 ms for women and >450 ms for men. The 30-day MACE occurred in 336 (13%) patients. QTc500_Group showed higher 30-day MACE than did those without (20.1% vs 12.5%, P = 0.003), with corresponding adjusted OR of 1.24 (95% CI: 1.06-1.46, P = 0.007). However, QTcP_Group showed comparable 30-day MACE (13.3% vs 12.8% without prolonged QTc, P = 0.764). Significant risk factors for QTc > 500 ms development were advanced liver disease, female sex, hypokalemia, hypocalcemia, high left ventricular end-diastolic volume, and tachycardia.

CONCLUSION

Our results revealed that, among ESLD patients, a novel threshold of QTc > 500 ms was associated with post-LT 30-day MACE but not with conventional threshold, indicating that a longer QTc threshold should be considered for this unique patient population.

Unusual Cause of Bidirectional Ventricular Rhythm

Bidirectional ventricular tachycardia (BDVT), a rare ventricular arrhythmia, is commonly caused by digitalis toxicity or channelopathies and is rarely caused by aconite toxicity, myocarditis, infarction, or sarcoidosis. This paper describes a patient with BDVT, recurrent syncope, myocardial disarray, and interstitial fibrosis on histology but normal results on echocardiography with variants in the TTN, KCNH2, and GATA4 genes. (Level of Difficulty: Advanced.)

Evaluation of cardiac functions in children with Duchenne Muscular Dystrophy: A prospective case-control study

Background

Duchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy. The incidence of cardiomyopathy in DMD increases with age, so its early detection is important because institution of cardioprotective medical therapies may slow adverse remodeling and attenuate heart failure symptoms in these patients.

Objective

To assess the cardiac functions in children clinically suspected to have DMD.

Methods

Over a one-year period, 28 male children aged from 3 to 18 years old, who met the criteria for diagnosis of DMD compared to 47 healthy controls children, were approached to participate in the study. The included children were subjected to full clinical examination, and blood samples were collected to determine creatinine phosphokinase (CPK), troponin I enzyme, myoglobin and lactate dehydrogenase (LDH) enzyme level. Echocardiography and 12-leads electrocardiogram (ECG) were also done for children in both groups. Data were analyzed using Independent-samples t-test, Mann-Whitney U, Chi square, and Fisher’s exact test.

Results

The mean age of the cases group was 7.29±3.24 years versus 8.06±2.86 years for controls. In DMD group, 25% had positive family history of DMD while 35.7% of them had positive consanguinity. All cases had elevated CPK level while CPK level in controls was normal (p<0.0001). LDH level was elevated in 19 cases (67.86%) of DMD while all controls children had normal LDH level (p<0.0001). Furthermore, the mean serum myoglobin level of DMD patients was higher relative to that of healthy controls (39.39±7.25 versus 33.68 ±12.38 ng/ml respectively) (p=0.01). Echocardiography of our patients revealed that seven cases (25%) had low ejection fraction (EF) and fraction shortening (FS). In addition, all controls children had normal EF (p<0.0001) and normal FS (p<0.0001). Interestingly, ECG showed that 28.57% of cases had sinus tachycardia vs. 6.88% for controls (p=0.0001). Prolonged QTc interval was present in 39.29% of cases (mean 431.39±43.60) while all controls had normal QTc duration for age (mean of 415.17±25.2) (p<0.0001).

Conclusion

ECG manifestations in children with DMD in the form of sinus tachycardia and prolonged QTc interval are an early alarm for developing cardiomyopathy before overt echocardiographic findings appear.

Evaluation of Abdominal Fetal Electrocardiography in Early Intrauterine Growth Restriction

Objectives: This descriptive study was performed to evaluate the capability of a non-invasive transabdominal electrocardiographic system to extract clear fetal electrocardiographic (FECG) measurements from intrauterine growth restricted (IUGR) fetuses and to assess whether abdominal FECG parameters can be developed as markers for evaluating the fetal cardiac status in IUGR.

Methods: Transabdominal FECG was attempted in 20 controls and 15 IUGR singleton pregnancies at 20+0−33+6 weeks gestation. Standard ECG parameters were compared between the study groups and evaluated for their correlation. Accuracy for the prediction of IUGR by cut off values of the different FECG parameters was also determined.

Results: Clear P-QRST complexes were recognized in all cases. In the IUGR fetuses, the QT and QTc intervals were significantly prolonged (p = 0.017 and p = 0.002, respectively). There was no correlation between ECG parameters and Doppler or other indices to predict IUGR. The generation of cut off values for detecting IUGR showed increasing sensitivities but decreasing specificities with the prolongation of ECG parameters.

Conclusion: The study of fetal electrocardiophysiology is now feasible through a non-invasive transabdominal route. This study confirms the potential of FECG as a clinical screening tool to aid diagnosis and management of fetuses after key limitations are addressed. In the case of IUGR, both QT and QTc intervals were significantly prolonged and thus validate earlier study findings where both these parameters were found to be markers of diastolic dysfunction. This research is a useful prelude to a test of accuracy and Receiver Operating Characteristics (ROC) study.

Evaluation of Prolonged QT Interval: Structural Heart Disease Mimicking Long QT Syndrome

BACKGROUND

In about 20-25% of patients with congenital long QT syndrome (LQTS) a causative pathogenic mutation is not found. The aim of this study was to explore the prevalence of alternative cardiac diagnoses among patients exhibiting prolongation of QT interval with negative genetic testing for LQTS genes.

METHODS

We conducted a retrospective analysis of 239 consecutive patients who were evaluated in the inherited arrhythmia clinic at the Toronto General Hospital between July 2013 and December 2015 for possible LQTS. A detailed review of the patients' charts, electrocardiograms, and imaging was carried out.

RESULTS

The analysis included 56 gene-negative patients and 61 gene-positive patients. Of the gene-negative group, 25% had structural heart disease compared to only 1.6% of gene-positive patients (P < 0.001). Structural heart disease was more likely if only one abnormal QTc parameter was found in the course of the evaluation (35.2% vs 9.1%, P = 0.01). The most common structural cardiac pathology was bileaflet mitral valve prolapse (8.9%). No gene-positive patient had episodes of nonsustained ventricular tachycardia, compared to seven of the gene-negative patients (0% vs 12.5%, P = 0.005).

CONCLUSIONS

Structural pathology was detected in a quarter of gene-negative patients evaluated for possible LQTS. Hence, cardiac imaging and Holter monitoring should be strongly encouraged to rule out structural heart disease in this population.

Influence of steroid hormones on ventricular repolarization

QT interval prolongation, corrected for heart rate (QTc), either spontaneous or drug-induced, is associated with an increased risk of torsades de pointes and sudden death. Women have longer QTc than men and are at higher risk of torsades de pointes, particularly during post-partum and the follicular phase. Men with peripheral hypogonadism have longer QTc than healthy controls. The role of the main sex steroid hormones has been extensively studied with inconsistent findings. Overall, estradiol is considered to promote QTc lengthening while progesterone and testosterone shorten QTc. New findings suggest more complex regulation of QTc by sex steroid hormones involving gonadotropins (i.e. follicle-stimulating hormone), the relative concentrations of sex steroid hormones (which depends on gender, i.e., progesterone/estradiol ratio in women). Aldosterone, another structurally related steroid hormone, can also prolong ventricular repolarization in both sex. Better understanding of pathophysiological hormonal processes which may lead to increased susceptibility of women (and possibly hypogonadic men) to drug-induced arrhythmia may foster preventive treatments (e.g. progesterone in women). Exogenous hormonal intake might offer new therapeutic opportunities or, alternatively, increase the risk of torsades de pointes. Some exogenous sex steroids may also have paradoxical effects on ventricular repolarization. Lastly, variations of QTc in women linked to the menstrual cycle and sex hormone fluctuations are generally ignored in regulatory thorough QT studies. Investigators and regulatory agencies promoting inclusion of women in thorough QT studies should be aware of this source of variability especially when studying drugs over several days of administration.

QRS Fragmentation and QTc Duration Relate to Malignant Ventricular Tachyarrhythmias and Sudden Cardiac Death in Patients with Hypertrophic Cardiomyopathy

BACKGROUND

QRS fragmentation (fQRS) and prolonged QTc interval on surface ECG are prognostic in various cardiomyopathies other than hypertrophic cardiomyopathy (HCM). The association between fQRS and prolonged QTc duration with occurrence of ventricular tachyarrhythmias or sudden cardiac death (VTA/SCD) in patients with HCM was explored.

METHODS AND RESULTS

One hundred and ninety-five clinical HCM patients were studied. QTc duration was derived applying Bazett's formula; fQRS was defined as presence of various RSR' patterns, R or S notching and/or >1 additional R wave in any non-aVR lead in patients without pacing or (in)complete bundle branch block. The endpoints comprised SCD, ECG documented sustained VTA (tachycardia or fibrillation) or appropriate implantable cardioverter defibrillator (ICD) therapies (antitachycardia pacing [ATP] or shock) for VTA in ICD recipients (n = 58 [30%]). QT prolonging drugs recipients were excluded. After a median follow-up of 5.7 years (IQR 2.7-9.1), 26 (13%) patients experienced VTA or SCD. Patients with fQRS in ≥3 territories (inferior, lateral, septal, and/or anterior) (p = 0.004) or QTc ≥460 ms (p = 0.009) had worse cumulative survival free of VTA/SCD than patients with fQRS in <3 territories or QTc <460 ms. fQRS in ≥3 territories (ß 4.5, p = 0.020, 95%CI 1.41-14.1) and QTc ≥460 ms (ß 2.7, p = 0.037, 95%CI 1.12-6.33) were independently associated with VTA/SCD. Likelihood ratio test indicated assessment of fQRS and QTc on top of conventional SCD risk factors provides incremental predictive value for VTA/SCD (p = 0.035).

CONCLUSIONS

Both fQRS in ≥3 territories and QTc duration are associated with VTA/SCD in HCM patients, independently of and incremental to conventional SCD risk factors.

Regulation of the human ether-a-go-go-related gene (hERG) channel by Rab4 protein through neural precursor cell-expressed developmentally down-regulated protein 4-2 (Nedd4-2)

The human ether-a-go-go-related gene (hERG) encodes the pore-forming α-subunit of the rapidly activating delayed rectifier K(+) channel in the heart, which plays a critical role in cardiac action potential repolarization. Dysfunction of IKr causes long QT syndrome, a cardiac electrical disorder that predisposes affected individuals to fatal arrhythmias and sudden death. The homeostasis of hERG channels in the plasma membrane depends on a balance between protein synthesis and degradation. Our recent data indicate that hERG channels undergo enhanced endocytic degradation under low potassium (hypokalemia) conditions. The GTPase Rab4 is known to mediate rapid recycling of various internalized proteins to the plasma membrane. In the present study, we investigated the effect of Rab4 on the expression level of hERG channels. Our data revealed that overexpression of Rab4 decreases the expression level of hERG in the plasma membrane. Rab4 does not affect the expression level of the Kv1.5 or EAG K(+) channels. Mechanistically, our data demonstrate that overexpression of Rab4 increases the expression level of endogenous Nedd4-2, a ubiquitin ligase that targets hERG but not Kv1.5 or EAG channels for ubiquitination and degradation. Nedd4-2 undergoes self- ubiquitination and degradation. Rab4 interferes with Nedd4-2 degradation, resulting in an increased expression level of Nedd4-2, which targets hERG. In summary, the present study demonstrates a novel pathway for hERG regulation; Rab4 decreases the hERG density at the plasma membrane by increasing the endogenous Nedd4-2 expression.

Barth syndrome

First described in 1983, Barth syndrome (BTHS) is widely regarded as a rare X-linked genetic disease characterised by cardiomyopathy (CM), skeletal myopathy, growth delay, neutropenia and increased urinary excretion of 3-methylglutaconic acid (3-MGCA). Fewer than 200 living males are known worldwide, but evidence is accumulating that the disorder is substantially under-diagnosed. Clinical features include variable combinations of the following wide spectrum: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), endocardial fibroelastosis (EFE), left ventricular non-compaction (LVNC), ventricular arrhythmia, sudden cardiac death, prolonged QTc interval, delayed motor milestones, proximal myopathy, lethargy and fatigue, neutropenia (absent to severe; persistent, intermittent or perfectly cyclical), compensatory monocytosis, recurrent bacterial infection, hypoglycaemia, lactic acidosis, growth and pubertal delay, feeding problems, failure to thrive, episodic diarrhoea, characteristic facies, and X-linked family history. Historically regarded as a cardiac disease, BTHS is now considered a multi-system disorder which may be first seen by many different specialists or generalists. Phenotypic breadth and variability present a major challenge to the diagnostician: some children with BTHS have never been neutropenic, whereas others lack increased 3-MGCA and a minority has occult or absent CM. Furthermore, BTHS was first described in 2010 as an unrecognised cause of fetal death. Disabling mutations or deletions of the tafazzin (TAZ) gene, located at Xq28, cause the disorder by reducing remodeling of cardiolipin, a principal phospholipid of the inner mitochondrial membrane. A definitive biochemical test, based on detecting abnormal ratios of different cardiolipin species, was first described in 2008. Key areas of differential diagnosis include metabolic and viral cardiomyopathies, mitochondrial diseases, and many causes of neutropenia and recurrent male miscarriage and stillbirth. Cardiolipin testing and TAZ sequencing now provide relatively rapid diagnostic testing, both prospectively and retrospectively, from a range of fresh or stored tissues, blood or neonatal bloodspots. TAZ sequencing also allows female carrier detection and antenatal screening. Management of BTHS includes medical therapy of CM, cardiac transplantation (in 14% of patients), antibiotic prophylaxis and granulocyte colony-stimulating factor (G-CSF) therapy. Multidisciplinary teams/clinics are essential for minimising hospital attendances and allowing many more individuals with BTHS to live into adulthood.

Evaluation of cardiac performance by abdominal fetal ECG in twin-to-twin transfusion syndrome

OBJECTIVE

To investigate fetal cardiac performance by abdominal fetal electrocardiography (ECG) in monochorionic diamniotic pregnancies with twin-to-twin transfusion syndrome (TTTS-MCDA).

METHODS

Abdominal fetal ECG was attempted in 16 singleton, 21 non-TTTS-MCDA, and 14 TTTS-MCDA pregnancies at 16-27 weeks' gestation. Standard ECG parameters were compared across study groups and evaluated for their correlation with Doppler ultrasound indices.

RESULTS

Clear P-QRST complexes were recognized in all cases. In the TTTS-MCDA pregnancies, the QT interval and QTc were significantly longer than in both singletons and the non-TTTS-MCDA pregnancies (p = 0.002 and p = 0.0002, respectively), whereas in the recipient fetus, both the PR interval and PR/RR were significantly longer when compared with all other study groups (p = 0.019 and p = 0.012, respectively). Further comparison with Doppler ultrasound indices yielded significant reciprocal correlations between ductus venosus pulsatility index and the QT interval (r = 0.552, p = 0.041) and between umbilical artery pulsatility index and PR/RR (r = 0.654, p = 0.011) both demonstrated in recipient fetuses alone.

CONCLUSIONS

Abdominal fetal ECG is feasible in second-trimester twin pregnancies. In TTTS, there is evidence of a higher risk of cardiac dysfunction in the recipient twin.

A mutation in TNNC1-encoded cardiac troponin C, TNNC1-A31S, predisposes to hypertrophic cardiomyopathy and ventricular fibrillation

Defined as clinically unexplained hypertrophy of the left ventricle, hypertrophic cardiomyopathy (HCM) is traditionally understood as a disease of the cardiac sarcomere. Mutations in TNNC1-encoded cardiac troponin C (cTnC) are a relatively rare cause of HCM. Here, we report clinical and functional characterization of a novel TNNC1 mutation, A31S, identified in a pediatric HCM proband with multiple episodes of ventricular fibrillation and aborted sudden cardiac death. Diagnosed at age 5, the proband is family history-negative for HCM or sudden cardiac death, suggesting a de novo mutation. TnC-extracted cardiac skinned fibers were reconstituted with the cTnC-A31S mutant, which increased Ca(2+) sensitivity with no effect on the maximal contractile force generation. Reconstituted actomyosin ATPase assays with 50% cTnC-A31S:50% cTnC-WT demonstrated Ca(2+) sensitivity that was intermediate between 100% cTnC-A31S and 100% cTnC-WT, whereas the mutant increased the activation of the actomyosin ATPase without affecting the inhibitory qualities of the ATPase. The secondary structure of the cTnC mutant was evaluated by circular dichroism, which did not indicate global changes in structure. Fluorescence studies demonstrated increased Ca(2+) affinity in isolated cTnC, the troponin complex, thin filament, and to a lesser degree, thin filament with myosin subfragment 1. These results suggest that this mutation has a direct effect on the Ca(2+) sensitivity of the myofilament, which may alter Ca(2+) handling and contribute to the arrhythmogenesis observed in the proband. In summary, we report a novel mutation in the TNNC1 gene that is associated with HCM pathogenesis and may predispose to the pathogenesis of a fatal arrhythmogenic subtype of HCM.

Prevalence and clinical correlates of QT prolongation in patients with hypertrophic cardiomyopathy

AIMS

Congenital or acquired QT prolongation is a risk factor for life-threatening arrhythmias. In patients with hypertrophic cardiomyopathy (HCM), the QT interval may be intrinsically prolonged. However, the prevalence, cause, and significance of QT prolongation among patients with HCM are unknown.

METHODS AND RESULTS

After exclusion of patients on QT-prolonging drugs, a blinded, retrospective analysis of electrocardiograms, echocardiograms, and genotype status in 479 unrelated patients with HCM [201 females, age at diagnosis 41 ± 18 years, maximal left ventricular wall thickness (MLVWT) 22 ± 6 mm] from two independent centres was performed. The mean QTc was 440 ± 28 ms. The QTc exceeded 480 ms in 13% of patients. Age, gender, family history of HCM or sudden cardiac arrest, and genotype status had no association with QTc. Patients with a QTc over 480 ms were more symptomatic at diagnosis (P < 0.001), had a higher MLVWT (P = 0.03), were more obstructive (P < 0.001), and were more likely to have undergone septal reduction therapy (P = 0.02). There was a weak but significant direct linear relationship between QTc and peak outflow gradient (r(2) = 0.05, P < 0.0001).

CONCLUSIONS

Compared with <1 in 200 otherwise healthy adults, QT prolongation (QTc > 480 ms) was present in 1 out of 8 patients with HCM. The QTc was partly reflective of the degree of cardiac hypertrophy and left ventricular outflow tract obstruction. Because of its pro-arrhythmic potential and its potential relevance to management and risk stratification, routine QTc assessment should be performed in patients with HCM, particularly when concomitant use of QT-prolonging medications is considered.

Heart rate-corrected QT interval and QT dispersion in patients with pulmonary hypertension

OBJECTIVE

Heart rate-corrected QT interval (QTc) and QTc dispersion (QTcd) are increased and associated with ventricular arrhythmia and an increase in sudden death in a variety of diseases. This study aimed to examine QTc and QTcd in pulmonary hypertension and assess their relationship with pulmonary arterial pressure.

PATIENTS AND METHODS

A total of 201 patients who had undergone right heart catheterization for a preliminary diagnosis of pulmonary hypertension between December 2003 and July 2008 were included in the study. Resting 12-lead electrocardiogram was recorded. QT interval was measured manually and corrected using Bazett's formula. Patients were divided into groups with mild-to-moderate and severe pulmonary hypertension and a control group according to mean pulmonary arterial pressure.

RESULTS

In all observed cases, mean QTc was higher in severe pulmonary hypertension than in controls (428.6 +/- 32.8 ms vs. 411.1 +/- 28.4 ms, P = 0.018) and QTcd was higher in mild-to-moderate (60.1 +/- 17.2 ms) and severe pulmonary hypertension (63.9 +/- 20.5 ms) than in controls (47.3 +/- 10.6 ms) (P = 0.031; P = 0.004). In men, there was no significant difference in mean QTc and QTcd. In women, mean QTc was higher in severe pulmonary hypertension than in controls (436.1 +/- 39.4 ms vs. 407.6 +/- 24.8 ms, P = 0.037) and QTcd was higher in severe pulmonary hypertension (68.5 +/- 20.9 ms) than in both the controls (45.1 +/- 12.6 ms) and patients with mild-to-moderate pulmonary hypertension (58.6 +/- 14.7 ms) (P = 0.002; P = 0.003). In addition, in women with pulmonary hypertension, mean QTc and QTcd were positively correlated to mean pulmonary arterial pressure (r = 0.207, P = 0.03; r = 0.236, P = 0.012).

CONCLUSIONS

In women with pulmonary hypertension, mean QTc and QTcd are positively correlated to mean pulmonary arterial pressure and are significantly increased in patients with severe pulmonary hypertension.

Drug-sensitized zebrafish screen identifies multiple genes, including GINS3, as regulators of myocardial repolarization

BACKGROUND

Cardiac repolarization, the process by which cardiomyocytes return to their resting potential after each beat, is a highly regulated process that is critical for heart rhythm stability. Perturbations of cardiac repolarization increase the risk for life-threatening arrhythmias and sudden cardiac death. Although genetic studies of familial long-QT syndromes have uncovered several key genes in cardiac repolarization, the major heritable contribution to this trait remains unexplained. Identification of additional genes may lead to a better understanding of the underlying biology, aid in identification of patients at risk for sudden death, and potentially enable new treatments for susceptible individuals.

METHODS AND RESULTS

We extended and refined a zebrafish model of cardiac repolarization by using fluorescent reporters of transmembrane potential. We then conducted a drug-sensitized genetic screen in zebrafish, identifying 15 genes, including GINS3, that affect cardiac repolarization. Testing these genes for human relevance in 2 concurrently completed genome-wide association studies revealed that the human GINS3 ortholog is located in the 16q21 locus, which is strongly associated with QT interval.

CONCLUSIONS

This sensitized zebrafish screen identified 15 novel myocardial repolarization genes. Among these genes is GINS3, the human ortholog of which is a major locus in 2 concurrent human genome-wide association studies of QT interval. These results reveal a novel network of genes that regulate cardiac repolarization.

Zebrafish genetic models for arrhythmia

Over the last decade the zebrafish has emerged as a major genetic model organism. While stimulated originally by the utility of its transparent embryos for the study of vertebrate organogenesis, the success of the zebrafish was consolidated through multiple genetic screens, sequencing of the fish genome by the Sanger Center, and the advent of extensive genomic resources. In the last few years the potential of the zebrafish for in vivo cell biology, physiology, disease modeling and drug discovery has begun to be realized. This review will highlight work on cardiac electrophysiology, emphasizing the arenas in which the zebrafish complements other in vivo and in vitro models; developmental physiology, large-scale screens, high-throughput disease modeling and drug discovery. Much of this work is at an early stage, and so the focus will be on the general principles, the specific advantages of the zebrafish and on future potential.

QT intervals in metabolic dilated cardiomyopathy

OBJECTIVES

The present study determined the prevalence of dilated cardiomyopathy together with prolonged corrected QT (QTc) intervals in children. The study also examined whether an association exists between prolonged QTc intervals and ventricular dysrhythmia in a patient cohort with dilated cardiomyopathy.

BACKGROUND

The morbidity and mortality for pediatric patients with dilated cardiomyopathy remains high and is a clinical challenge. The patient population includes a significant number of Hutterite patients with metabolic disease associated with dilated cardiomyopathy.

METHODS

Thirty-eight pediatric patients with dilated cardiomyopathy were reviewed for the presence of prolonged QTc and dysrhythmias. Eleven patients had a metabolic etiology for their dilated cardiomyopathy.

RESULTS

Thirty-six per cent of the patient cohort had a long QTc interval. After 50 months of follow-up, the probability of survival for a child with a long QTc interval was approximately 50%. The probability of survival for a child with a normal QTc interval was 72%. Seventy per cent of the patients who died had a metabolic etiology for their dilated cardiomyopathy and a long QTc.

CONCLUSIONS

Dilated cardiomyopathy may be associated with a prolonged QTc and may increase the patient's risk for sudden death. The presence of a metabolic etiology for dilated cardiomyopathy increases the risk of death.

Dilated cardiomyopathy masquerading as long QT syndrome

Atrioventricular block has been described in association with cases of long QT syndrome and mortality is increased in this subgroup. We describe an infant with congenital QT prolongation and atrioventricular block with normal cardiac function, leading to the initial diagnosis of long QT syndrome. She subsequently developed dilated cardiomyopathy requiring cardiac transplantation. We postulate that the presenting electrocardiograph abnormalities were early manifestations of the myocardial disease, preceding the development of myocardial dysfunction by several months. The need for heightened surveillance in cases of QT prolongation with atrioventricular block is amplified by the possibility of an evolving cardiomyopathy.

Importance of hepatitis C coinfection in the development of QT prolongation in HIV-infected patients

BACKGROUND

Case reports and unblinded studies suggest that human immunodeficiency virus (HIV) disease is associated with QT prolongation and torsade de pointes ventricular tachycardia. Hepatitis C coinfection is common in patients with HIV disease, and cirrhosis is also associated with QT prolongation. We therefore undertook a systematic analysis of the role of liver injury, nutritional state, and coinfection with hepatitis C in the etiology of QT prolongation in HIV disease.

METHODS

We performed a blinded, controlled retrospective cohort study of 1648 patients over a 3-year period at a university-affiliated municipal hospital. All electrocardiograms were included if patients with HIV disease had measurements of CD4 count and viral load within 3 months and serum electrolytes within 30 days (n = 816). Control subjects were chosen randomly from the general medicine service (n = 832). QT interval was measured in lead II and corrected for heart rate by Bazett's formula (QTc).

RESULTS

QTc was slightly but significantly longer in patients with HIV disease than in controls (443 +/- 37 vs 436 +/- 36 milliseconds, P < .001). Patients with hepatitis C had more pronounced QTc prolongation (452 +/- 41 vs 437 +/- 35 milliseconds, P < .001). CD4 count, HIV viral load, and HIV medications had no effect on QTc. When patients with hepatitis C were excluded from the analysis, there was no statistical difference between patients with HIV disease and controls (438 +/- 34 vs 436 +/- 36 milliseconds, P = .336). Multiple linear regression revealed that both HIV and hepatitis C infection predicted QTc prolongation, as did age, female sex, history of hypertension, use of opiates, low serum K+ and albumin, and high AST. Hepatitis C coinfection nearly doubled the risk of QTc of 470 milliseconds or greater in patients with HIV disease (29.6% vs 15.8%, P < .001).

CONCLUSIONS

Human immunodeficiency virus and hepatitis C infections both independently prolong QTc. Coinfection with hepatitis C greatly increases the likelihood of clinically significant QTc prolongation in patients with HIV disease.

The usefulness of surface electrocardiogram as a prognostic predictor in children with idiopathic dilated cardiomyopathy

We investigated the interrelations between surface electrocardiographic changes and clinical outcomes in children with idiopathic dilated cardiomyopathy (DCMP). 33 patients (19 boys, 14 girls) were classified into two groups; group I (15) who were in poor clinical status or dead; and group II (18) who showed good clinical status. Group I had larger LV dimensions compared to group II (Gr I vs. Gr II; LVEDD, 52 +/-11 vs. 42+/-7 (mm); LVESD, 43+/-12 vs. 30+/-5 (mm); p<0.05). QRS duration was prolonged in Gr I compared to Gr II and normal (Gr I, 84+/-28; Gr II, 66+/-12; normal control, 67+/-9). The QRS duration was correlated with the dimensions of left ventricle (LV). Corrected QT and JT interval and dispersions of QT in the DCMP group showed a significant difference compared to the normal control, however there was no significant difference between Gr I and II. In conclusion, QRS duration was correlated with ventricular dimension and clinical outcome in children with idiopathic dilated cardiomyopathy. Irrespective of increased ventricular inhomogeneity, QT dispersion could not be used to predict long-term prognosis.

Pharmacogenetic aspects of drug-induced torsade de pointes: potential tool for improving clinical drug development and prescribing

Drug-induced torsade de pointes (TdP) has proved to be a significant iatro-genic cause of morbidity and mortality and a major reason for the withdrawal of a number of drugs from the market in recent times. Enzymes that metabolise many of these drugs and the potassium channels that are responsible for cardiac repolarisation display genetic polymorphisms. Anecdotal reports have suggested that in many cases of drug-induced TdP, there may be a concealed genetic defect of either these enzymes or the potassium channels, giving rise to either high plasma drug concentrations or diminished cardiac repolarisation reserve, respectively. The presence of either of these genetic defects may predispose a patient to TdP, a potentially fatal adverse reaction, even at therapeutic dosages of QT-prolonging drugs and in the absence of other risk factors. Advances in pharmacogenetics of drug metabolising enzymes and pharmacological targets, together with the prospects of rapid and inexpensive genotyping procedures, promise to individualise and improve the benefit/risk ratio of therapy with drugs that have the potential to cause TdP. The qualitative and the quantitative contributions of these genetic defects in clinical cases of TdP are unclear because not all of the patients with TdP are routinely genotyped and some relevant genetic mutations still remain to be discovered. There are regulatory guidelines that recommend strategies aimed at uncovering the risk of TdP associated with new chemical entities during their development. There are also a number of guidelines that recommend integrating pharmacogenetics in this process. This paper proposes a strategy for integrating pharmacogenetics into drug development programmes to optimise association studies correlating genetic traits and endpoints of clinical interest, namely failure of efficacy or development of repolarisation abnormalities. Until pharmacogenetics is carefully integrated into all phases of development of QT-prolonging drugs and large-scale studies are undertaken during their post-marketing use to determine the genetic components involved in induction of TdP, routine genotyping of patients remains unrealistic. Even without this pharmacogenetic data, the clinical risk of TdP can already be greatly minimised. Clinically, a substantial proportion of cases of TdP are due to the use of either high or usual dosages of drugs with potential to cause TdP in the presence of factors that inhibit drug metabolism. Therefore, choosing the lowest effective dose and identifying patients with these non-genetic risk factors are important means of minimising the risk of TdP. In view of the common secondary pharmacology shared by these drugs, a standard set of contraindications and warnings have evolved over the last decade. These include factors responsible for pharmacokinetic or pharmacodynamic drug interactions. Among the latter, the more important ones are bradycardia, electrolyte imbalance, cardiac disease and co-administration of two or more QT-prolonging drugs. In principle, if large scale prospective studies can demonstrate a substantial genetic component, pharmacogenetically driven prescribing ought to reduce the risk further. However, any potential benefits of pharmacogenetics will be squandered without any reduction in the clinical risk of TdP if physicians do not follow prescribing and monitoring recommendations.

Abnormal QT interval variability in patients with hypertrophic cardiomyopathy

We sought to determine QT variability pattern in patients with hypertrophic cardiomyopathy (HCM) and its relationship with the risk of syncope. QT interval variability was assessed from 24-hour Holter monitoring in 10 HCM patients with history of syncope, 10 HCM patients without history of syncope, and 10 healthy subjects. QT variability was higher in patients with HCM, in particular in those with history of syncope, than in healthy controls. Time domain QT variability did not vary between waking and sleeping hours in HCM patients, whereas it was significantly shorter while asleep in the control group. Increased QT SDANN identified HCM patients with history of syncope with an accuracy of 75%. Our data show that QT variability is abnormal in HCM patients and indirectly support the concept that arrhythmia-related syncope in these patients may be, at least in part, related to an altered control of repolarization.

Relation between QT duration and maximal wall thickness in familial hypertrophic cardiomyopathy

BACKGROUND

QT abnormalities have been reported in left ventricular hypertrophy and hypertrophic cardiomyopathy.

OBJECTIVE

To determine the relation between left ventricular hypertrophy and increased QT interval in familial hypertrophic cardiomyopathy.

METHODS

The QT interval was measured in 206 genotyped adult subjects with familial hypertrophic cardiomyopathy from 15 unrelated families carrying mutations in the beta myosin heavy chain (beta-MHC) gene (five families, n = 68) or the cardiac myosin binding protein C (MyBPC) gene (10 families, n = 138). Subjects were classified as genetically unaffected (controls, n = 112), affected with left ventricular hypertrophy (penetrants, n = 58), or affected without left ventricular hypertrophy (non-penetrants, n = 36).

RESULTS

There was a significant increase in QTmax and QTmin from controls to non-penetrants and penetrants for both the MyBPC group (p < or = 0.001 and p < or = 0.001, respectively) and the beta-MHC group (p < or = 0.001 and p < or = 0.001, respectively). In the MyBPC group, the increase in the QT interval could be explained by increased left ventricular hypertrophy. In the beta-MHC group, non-penetrants had a significantly longer QTmax than controls despite the absence of left ventricular hypertrophy, and a similar QT interval to penetrants despite a lesser degree of left ventricular hypertrophy.

CONCLUSIONS

In familial hypertrophic cardiomyopathy, genetically affected subjects without left ventricular hypertrophy may have a prolonged QT duration, which depends not only on the degree of left ventricular hypertrophy, when present, but also on the causative mutation.

Torsade de pointes in a child with acute rheumatic fever

Ventricular arrhythmias are uncommon in acute rheumatic carditis. We report the case of a child who presented with rheumatic carditis, prolonged corrected QT interval, and torsade de pointes. The episodes of torsade were controlled with beta-blockade and cardiac pacing. The child subsequently died as a result of brain injury; the autopsy revealed classic findings of acute rheumatic carditis.

Prolongation of QT interval and ventricular septal hypertrophy

Long QT syndrome (LQTS) is a prime example of interplay between molecular biology, cellular physiology, and organ physiology. Both the congenital and acquired forms of LQTS are due to intrinsic and/or acquired abnormalities of the ionic currents responsible for cardiac repolarization. We analyzed the QTc interval, QRS axes and interventricular septal thickness (IVST) in 41 patients who had a prolonged QT interval on routine electrocardiography (ECG) (5 females and 36 males, mean age 65+/-13 years). The QRS axis of patients in the LQTS group (27+/-49 degrees) was significantly lower (p < 0.05) than in the control group (46+/-26 degrees). However, the IVST in the LQTS group (10+/-2 mm) was significantly thicker than in the control group (9+/-1 mm) (p < 0.05), while the WTd was not significantly different. The QTc interval in patients with ventricular septal hypertrophy (IVST > or = 12 min, 478.8+/-7.9 msec) was significantly longer (p < 0.05) than in the normal group (IVST < 12 mm, 472.1+/-17.5 msec). In conclusion, the results of this preliminary study suggest that prolongation of the QT interval on ECG should prompt screening for electrocardiographic evidence of ventricular hypertrophy in patients with this disease.

Temporal repolarization lability in hypertrophic cardiomyopathy caused by beta-myosin heavy-chain gene mutations

BACKGROUND

Certain genetic mutations associated with hypertrophic cardiomyopathy (HCM) carry an increased risk of sudden death. QT variability identifies patients at a high risk for sudden death from ventricular arrhythmias. We tested whether patients with HCM caused by beta-myosin heavy-chain (beta-MHC) gene mutations exhibit labile ventricular repolarization using beat-to-beat QT variability analysis.

METHODS AND RESULTS

We measured the QT variability index and heart rate-QT interval coherence from Holter monitor recordings in 36 patients with HCM caused by known beta-MHC gene mutations and in 26 age- and sex-matched controls. There were 7 distinct beta-MHC gene mutations in these 36 patients; 9 patients had HCM caused by the malignant Arg(403)Gln mutation and 8 patients had HCM caused by the more benign Leu(908)Val mutation. The QT variability index was higher in HCM patients than in controls (-1.24+/-0.17 versus -1. 58+/-0.38, P<0.01), and the greatest abnormality was detected in patients with the Arg(403)Gln mutation (-0.99+/-0.49 versus -1. 46+/-0.43 in controls, P<0.05). In keeping with this finding, coherence was lower for the entire HCM group than for controls (P<0. 001). Coherence was also significantly lower in patients with the Arg(403)Gln mutation compared with controls (P<0.05).

CONCLUSIONS

These findings suggest that (1) patients with HCM caused by beta-MHC gene mutations exhibit labile repolarization quantified by QT variability analysis and, hence, may be more at risk for sudden death from ventricular arrhythmias, and (2) indices of QT variability may be particularly abnormal in patients with beta-MHC gene mutations that are associated with a poor prognosis.

Circadian modulation of QT rate dependence in healthy volunteers: gender and age differences

QT rate dependence is known to be linked with both circadian variations of the autonomic tone and gender. However, age and heart rate variability (HRV) influences are not well established. The QT/RR relationship was evaluated, separately during the day and at night, on 24-hour electrocardiogram in 60 healthy subjects (30 men) divided into three homogeneous groups (group 1, 20-29; group 2 30-39; group 3, 40-50 years). QT rate dependence was larger during the day in both genders. Women showed stronger QT rate dependence (0.195 during the day vs. 0.154 in men P< .0001). The circadian modulation decreased with increasing age (day/night slope differences: group 1, 0.038; group 2, 0.031; group 3, 0.001; analysis of variance P<.05). In addition, QT rate dependence increased as mean RR decreased (r = -0.58, P<.0001) and decreased as HRV parameters increased. Multiple influences on QT rate dependence can be found: not only circadian and gender modulation, but also age, heart rate, and HRV interventions.

Abnormalities of the QT interval in primary disorders of autonomic failure

BACKGROUND

Experimental evidence shows that activation of the autonomic nervous system influences ventricular repolarization and, therefore, the QT interval on the ECG. To test the hypothesis that the QT interval is abnormal in autonomic dysfunction, we examined ECGs in patients with severe primary autonomic failure and in patients with congenital dopamine beta-hydroxylase (DbetaH) deficiency who are unable to synthesize norepinephrine and epinephrine.

SUBJECTS AND METHODS

Maximal QT and rate-corrected QT (QTc) intervals and adjusted QTc dispersion [(maximal QTc - minimum QTc on 12 lead ECG)/square root of the number of leads measured] were determined in blinded fashion from ECGs of 67 patients with primary autonomic failure (36 patients with multiple system atrophy [MSA], and 31 patients with pure autonomic failure [PAF]) and 17 age- and sex-matched healthy controls. ECGs of 5 patients with congenital DbetaH deficiency and 6 age- and sex-matched controls were also analyzed.

RESULTS

Patients with MSA and PAF had significantly prolonged maximum QTc intervals (492+/-58 ms(1/2) and 502+/-61 ms(1/2) [mean +/- SD]), respectively, compared with controls (450+/-18 ms(1/2), P < .05 and P < .01, respectively). A similar but not significant trend was observed for QT. QTc dispersion was also increased in MSA (40+/-20 ms(1/2), P < .05 vs controls) and PAF patients (32+/-19 ms(1/2), NS) compared with controls (21+/-5 ms(1/2)). In contrast, patients with congenital DbetaH deficiency did not have significantly different RR, QT, QTc intervals, or QTc dispersion when compared with controls.

CONCLUSIONS

Patients with primary autonomic failure who have combined parasympathetic and sympathetic failure have abnormally prolonged QT interval and increased QT dispersion. However, QT interval in patients with congenital DbetaH deficiency was not significantly different from controls. It is possible, therefore, that QT abnormalities in patients with primary autonomic failure are not solely caused by lesions of the sympathetic nervous system, and that the parasympathetic nervous system is likely to have a modulatory role in ventricular repolarization.

Verapamil therapy in infants with hypertrophic cardiomyopathy

We sought to evaluate the safety and efficacy of acute and chronic treatment with verapamil in infants with hypertrophic cardiomyopathy. Prior studies have shown an improvement in adults with hypertrophic cardiomyopathy who were treated with verapamil. Acutely, it reduced the degree of left ventricular outflow tract obstruction. Chronic therapy was associated with an improvement in symptoms and increased long-term survival. To date, no data are available on the efficacy of this drug in infants with hypertrophic cardiomyopathy. We evaluated prospectively the safety and efficacy of verapamil in infants. The acute and chronic effects of verapamil on infants with an echocardiographic diagnosis of hypertrophic cardiomyopathy were evaluated at a single institution between 1980 and 1994, with long-term follow-up available until 1996. Acute effects of an intravenous bolus of 0.1 mg/kg and infusion at 0.007 mg/kg/min were evaluated, where possible, in the cardiac catheterization laboratory. Oral verapamil at 3-5 mg/kg/day was started after catheterization. Follow-up included serial clinical, echocardiographic and Holter monitoring. A total of 22 patients were studied, 17 having a presumed diagnosis of primary hypertrophic cardiomyopathy including three with Noonan's syndrome. Acute infusion of the drug was well tolerated by all, without adverse electrophysiological effects. Haemodynamic effects were consistent with a negative inotropic action with significant falls in cardiac index (4.6+/-1.2 to 4.1+/-0.9 l/min/m2), systolic blood pressure (88+/-16 to 82+/-14 mmHg) and gradient across the left ventricular outflow tract (nine patients 48.2+/-30.4 to 28.4+/-24.1 mmHg). End-diastolic pressure was unchanged (14.0+/-6.8 to 13.9+/-4.7 mmHg). Three patients with primary hypertrophic cardiomyopathy died (two while being treated). In the group with primary hypertrophic cardiomyopathy continuing with long-term treatment, follow-up revealed regression in two, progression in three (two died) and stability in 10. For those treated, there was a trend towards improvement in clinical status. Verapamil is well tolerated acutely in infants with hypertrophic cardiomyopathy. The outcome was considerably better in these patients compared with prior reports, though careful long-term assessment is needed.

Normalization of acquired QT prolongation in humans by intravenous potassium

BACKGROUND

QT interval prolongation and dispersion have been implicated in serious arrhythmias in congestive heart failure (CHF) and the congenital and drug-induced long-QT syndromes (LQTS). In a subset of the congenital LQTS, infusion of potassium can correct QT abnormalities, consistent with in vitro increases in outward currents such as I(Kr) or I(Kl) when extracellular potassium concentration ([K+]o) is increased. Furthermore, increasing [K+]o decreases the potency of I(Kr)-blocking drugs in vitro. The purpose of this study was to test the hypothesis that increasing [K+]o corrects QT abnormalities in CHF and in subjects treated with quinidine.

METHODS AND RESULTS

KCl (maximum, 40 mEq) was infused into (1) 12 healthy subjects treated with quinidine sulfate (5 doses of 300 mg/5 h) or placebo and (2) 8 CHF patients and age-matched normal control subjects. Mean [K+] increased from 4 to 4.2 mEq/L to 4.7 to 5.2 mEq/L. Potassium infusion significantly reversed QTUc prolongation, especially in the precordial leads (quinidine, 590+/-79 to 479+/-35 [+/-SD] ms(1/2), P<.001; CHF, 521+/-110 to 431+/-47 ms(1/2), P<.05). There was no effect in either control group. Similarly, potassium decreased QTUc dispersion (quinidine, 210+/-62 to 130+/-75 ms(1/2), P<.01; CHF, 132+/-68 to 84+/-35 ms(1/2), P=.07) and was without effect in the control subjects. QT morphological abnormalities, including U waves and bifid T waves, were reversed by potassium.

CONCLUSIONS

Potentially arrhythmogenic QT abnormalities during quinidine treatment and in CHF can be nearly normalized by modest elevation of serum potassium.

New diagnostic options in hypertrophic cardiomyopathy

The pathophysiologic features and clinical manifestations of HCM have been elucidated by the introduction of several new diagnostic options. Knowledge of the molecular defects of HCM has advanced rapidly, and genetic screening studies have reemphasized the value of the standard electrocardiogram as an initial screening tool. Analysis of heart rate variability, late potentials, and QT dispersion were not found to be reliable prognostic markers in HCM. However, measurement of dispersion of conduction is probably a sensitive technique in identifying a high risk for sudden cardiac death. Significant developments include transthoracic and transesophageal echocardiography and their role in studying the mitral valve, early detection of left ventricular chamber dilatation, analysis of coronary flow, and intraoperative echocardiography. Finally, advances in the application of magnetic resonance imaging and positron-emission tomography are underway.

Dispersion of ventricular repolarization in hypertrophic cardiomyopathy

On an averaged QRS-T cycle from a 15-lead record (12-lead electrocardiogram + XYZ leads) and through interactive editing, four electrocardiographic indices of the dispersion of ventricular repolarization (DVR) are automatically computed and represent the maximal interlead difference of QT and JTend and QT and JTapex. The values of these indices were then examined in three clinical groups matched for age and sex: normal subjects (control), patients with left ventricular hypertrophy (LVH group), and patients with hypertrophic cardiomyopathy (HCM group) without ventricular arrhythmias and without interacting drugs. The mean values of all four DVR indices were significantly increased in the HCM group compared with the control group and the LVH group of another origin (ie, for the QTe dispersion index, the mean values and the 97.5th percentiles were, respectively, 65 +/- 18 ms and 97 ms in the HCM group, 41 +/- 25 ms and 79 ms in the LVH group, and 31 +/- 15 ms and 58 ms in the control group). The maximal QT interval was also significantly longer in the HCM group (464 +/- 30 ms) than in the LVH group (436 +/- 32 ms) and the control group (428 +/- 25 ms).

QT interval in cardiac amyloidosis

The aim of the study was to investigate whether cardiac amyloidosis is associated with QT interval abnormalities and ventricular arrhythmias. A controlled study of 30 patients was undertaken at a university cardiology department in a large referral hospital. Thirty patients (18 men, 12 women, mean age 56 +/- 12 years) with systemic amyloidosis verified by biopsy and strong indications of cardiac amyloidosis comprised the study group, with 30 healthy age- and sex-matched individuals serving as controls. Complete M-mode and two-dimensional echocardiographic study was undertaken and QT interval and QTc were calculated. All patients and controls underwent 24-h Holter monitoring for arrhythmias. Left ventricular (LV) wall thickening was found in all patients with cardiac amyloidosis. The LV mass in the patients with cardiac amyloidosis was significantly greater than that of the control group, as was the ratio LV mass/body surface area (p < 0.001). There was no significant difference in the max QT interval or in QTc dispersion between the two groups, although the max QTc was greater in the patients with cardiac amyloidosis. Patients with cardiac amyloidosis did not have a higher incidence of arrhythmias than the controls. Although patients with thickened cardiac walls due to cardiac amyloidosis have a prolonged QTc in comparison with controls, they do not show an increase in interlead QTc dispersion which might suggest the possibility of regional disturbances of the uniformity of repolarization. Patients with cardiac amyloidosis do not have a higher incidence of arrhythmias than controls.