An International Multicenter Evaluation of Type 5 Long QT Syndrome: A Low Penetrant Primary Arrhythmic Condition

BACKGROUND

Insight into type 5 long QT syndrome (LQT5) has been limited to case reports and small family series. Improved understanding of the clinical phenotype and genetic features associated with rare KCNE1 variants implicated in LQT5 was sought through an international multicenter collaboration.

METHODS

Patients with either presumed autosomal dominant LQT5 (N = 229) or the recessive Type 2 Jervell and Lange-Nielsen syndrome (N = 19) were enrolled from 22 genetic arrhythmia clinics and 4 registries from 9 countries. KCNE1 variants were evaluated for ECG penetrance (defined as QTc >460 ms on presenting ECG) and genotype-phenotype segregation. Multivariable Cox regression was used to compare the associations between clinical and genetic variables with a composite primary outcome of definite arrhythmic events, including appropriate implantable cardioverter-defibrillator shocks, aborted cardiac arrest, and sudden cardiac death.

RESULTS

A total of 32 distinct KCNE1 rare variants were identified in 89 probands and 140 genotype positive family members with presumed LQT5 and an additional 19 Type 2 Jervell and Lange-Nielsen syndrome patients. Among presumed LQT5 patients, the mean QTc on presenting ECG was significantly longer in probands (476.9±38.6 ms) compared with genotype positive family members (441.8±30.9 ms, P<0.001). ECG penetrance for heterozygous genotype positive family members was 20.7% (29/140). A definite arrhythmic event was experienced in 16.9% (15/89) of heterozygous probands in comparison with 1.4% (2/140) of family members (adjusted hazard ratio [HR] 11.6 [95% CI, 2.6-52.2]; P=0.001). Event incidence did not differ significantly for Type 2 Jervell and Lange-Nielsen syndrome patients relative to the overall heterozygous cohort (10.5% [2/19]; HR 1.7 [95% CI, 0.3-10.8], P=0.590). The cumulative prevalence of the 32 KCNE1 variants in the Genome Aggregation Database, which is a human database of exome and genome sequencing data from now over 140 000 individuals, was 238-fold greater than the anticipated prevalence of all LQT5 combined (0.238% vs 0.001%).

CONCLUSIONS

The present study suggests that putative/confirmed loss-of-function KCNE1 variants predispose to QT prolongation, however, the low ECG penetrance observed suggests they do not manifest clinically in the majority of individuals, aligning with the mild phenotype observed for Type 2 Jervell and Lange-Nielsen syndrome patients.

Assessment of aspirin resistance varies on a temporal basis in patients with ischaemic heart disease

Objective:

Laboratory tests including optical platelet aggregometry (OPA), platelet function analyser (PFA-100), and thromboxane B₂ (TXB₂) metabolite levels have been used to define aspirin resistance. This study characterised the prevalence of aspirin resistance in patients with ischaemic heart disease (IHD) and investigated the concordance and repeatability of these tests.

Design, setting and patients:

Consecutive outpatients with stable IHD were enrolled. They were commenced on 150 mg aspirin daily (day 0) and had platelet function assessment (OPA and PFA-100) and quantitative analysis of serum/urine TXB₂ at day ⩾7 and then at a second visit approximately 2 weeks later.

Main outcome measures:

We assessed the prevalence of aspirin resistance by each method, concordance between methods of measuring response to aspirin and association between time points to assess the predictability of response over time.

Results:

172 patients (62.7 (SD 8.7) years, 83.1% male) were recruited. At visits 1 and 2, respectively, 1.7% and 4.7% were aspirin resistant by OPA, whereas 22.1% and 20.3% were aspirin resistant by PFA-100. There were poor associations between PFA-100 and OPA, and between TXB₂ metabolites and platelet function tests. OPA and PFA-100 results were poorly associated between visits (κ = 0.16 and κ = 0.42, respectively) as were TXB₂ metabolites, suggesting that aspirin resistance is not predictable over time.

Conclusions:

The prevalence of aspirin resistance is dependent on the method of testing. Response varies on a temporal basis, indicating that testing on a single occasion is inadequate to diagnose resistance or guide therapy in a clinical setting.

ST segment elevation in lead aVR during exercise testing is associated with LAD stenosis

PURPOSE

To evaluate, in patients with chest pain, the diagnostic value of ST elevation (STE) in lead aVR during stress testing prior to (99m) Tc-sestamibi scanning correlating ischaemic territory with angiographic findings.

METHODS

Consecutive patients attending for (99m) Tc-sestamibi myocardial perfusion imaging (MPI) completed a treadmill protocol. Peak exercise ECGs were coded. STE >or=0.05 mV in lead aVR was considered significant. Gated perfusion images and findings at angiography were assessed.

RESULTS

STE in lead aVR occurred in 25% (138/557) of the patients. More patients with STE in aVR had a reversible defect on imaging compared with those who had no STE in aVR (41%, 56/138 vs 27%, 114/419, p=0.003). Defects indicating a left anterior descending artery (LAD) culprit lesion were more common in the STE in aVR group (20%, 27/138 vs 9%, 39/419, p=0.001). There was a trend towards coronary artery stenosis (>70%) in a double vessel distribution involving the LAD in those patients who had STE in aVR compared with those who did not (22%, 8/37 vs 5%, 4/77, p=0.06). Logistic regression analysis demonstrated that STE in aVR (OR 1.36, p=0.233) is not an independent predictor of inducible abnormality when adjusted for STD >0.1 mV (OR 1.69, p=0.026). However, using anterior wall defect as an end-point, STE in aVR (OR 2.77, p=0.008) was a predictor even after adjustment for STD (OR 1.43, p=0.281).

CONCLUSION

STE in lead aVR during exercise does not diagnose more inducible abnormalities than STD alone. However, unlike STD, which is not predictive of a territory of ischaemia, STE in aVR may indicate an anterior wall defect.

Bioavailability of two selegiline hydrochloride tablet products

The bioavailability of two selegiline HCl (CAS 14611-52-0) tablet products was compared in a single-blind, single-dose, randomised, two-way, cross-over study with 25 healthy volunteers. A test preparation of selegiline HCl (4 x 5 mg tablets) was compared to a reference preparation of selegiline HCl (4 x 5 mg tablets). The volunteers were randomised receiving each treatment once. Two clinic days were separated by a wash-out period of between 6 and 14 days. The variable AUC(0-infinity) was the primary characteristic of the extent of formation (bioavailability) of the selegiline metabolites, desmethylselegiline and methamphetamine. For desmethylselegiline the point estimate (90% confidence interval) of the "test/reference" mean ratio for the variable Cmax is 98.4% (91.2% to 106%), for AUC(0-infinity) 103% (97.6% to 109%), and for Cmax/ AUC(0-infinity) 95.6% (89.4% to 102%). For methamphetamine the point estimate (90% confidence interval) of the "test/reference" mean ratio for the variable Cmax is 101% (96.8% to 105%), for AUC(0-infinity) 102% (95.3% to 109%), and for Cmax/AUC(0-infinity) 99.0% (91.5% to 107%). The results of this study indicate that the test preparation is bioequivalent to the reference preparation with respect to both the rate and extent of formation of desmethylselegiline and methamphetamine.

Changes in the ultrastructure of rat myocardium induced by hyperkalaemia

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The structure and function of a slowly adapting touch corpuscle in hairy skin

1. Slowly adapting cutaneous mechanoreceptors, in the cat and primates, have been studied by histological and neurophysiological methods.2. Each touch corpuscle is a dome-shaped elevation of the epidermis, whose deepest layer contains up to fifty specialized tactile cells.3. Nerve plates, enclosed by the tactile cell (Merkel cells), are connected to a single myelinated axon in the dense collagenous core of the corpuscle.4. The corpuscle generated > 1000 impulses/sec when excited by vertical surface pressure. The response was highly localized and showed a low mechanical threshold, the frequency being dependent upon the velocity and amplitude of the displacement. There was a period of rapid adaptation before a sustained response which might continue for > 30 min.5. A quantitative analysis of the responses to excitation by displacements of differing amplitude, velocity and duration is included.6. The discharge of touch corpuscle units evoked by a mechanical stimulus was temperature-sensitive, and was enhanced by a fall in skin temperature.

The effects of divalent cations on the ultrastructure of the perfused rat heart

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Distribution of iron in maternal and foetal tissues from pregnant rhesus monkeys treated with a single intravenous infusion of [59Fe] iron dextran

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The structure of the satellite cells in skeletal muscle

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