Coinheritance of long QT syndrome and Kearns-Sayre syndrome

TNNI3 and KCNQ1 co-inherited variants in a family with hypertrophic cardiomyopathy and long QT phenotypes: A case report

QTc prolongation is reported in patients with hypertrophic cardiomyopathy (HCM). However, the causes of the QTc interval increase remain unclear. The main contribution to QTc prolongation in HCM is attributed to the myocardial hypertrophy and related structural damage. In a 24-year-old male proband, affected by HCM and long QTc, we identified by Next Generation Sequencing a pathogenic variant in gene TNNI3 co-inherited with a damaging variant in KCNQ1 gene. This evidence suggests the possibility that QTc interval prolongation and its dispersion in HCM could be associated not only to the severity of left ventricular hypertrophy but also to the co-inheritance of pathogenic variants related to both long QT Syndrome (LQTS) and HCM. Although the simultaneous presence of pathogenic variants in genes related to different heart diseases is extremely rare, counseling and genetic testing appear crucial for the clinical diagnosis. Screening of LQTS genes should be considered in HCM patients to clarify the origin of long QTc, to provide more information about the clinical presentation and to evaluate the incidence of the co-existence of LQTS/HCM gene variants that could occur more frequently than so far reported.

Kearns Sayre Syndrome: Looking beyond A-V conduction

A 15-year-old boy was diagnosed with Kayne Sayre Syndrome. He presented with pigmentary retinopathy, progressive ophthalmoplegia and complete heart block. He received a transvenous dual chamber pacemaker. Two years later he died suddenly while at home. This case highlights the importance of recognizing mechanisms other than heart block as a cause of sudden death in a patient with KSS.

Early cardiac evaluation in children with non-specific mitochondrial disease with isolated mitochondrial respiratory chain complex I defect

AIMS

We evaluated echocardiography and electrocardiography (ECG) results in children with non-specific mitochondrial disease (MD) in order to study early cardiac involvement, a well-known complication of the disease.

METHODS

Among non-specific MD children whose isolated mitochondrial respiratory chain complex I defect was confirmed by muscle biopsy and satisfied the criteria of MD, 27 who had no cardiac symptoms were evaluated by echocardiography and ECG.

RESULTS

Three (11.1%) out of the 27 non-specific MD patients had left ventricular ejection fraction of less than 55% and two of them (7.4%) had fractional shortening of less than 26%. ECG abnormalities were observed in 16 of the non-specific MD patients (59.3%). Prolongation of heart rate-corrected QT interval was seen in 11 (40.7%) and widening of the QRS interval in eight (29.6%). Left ventricular ejection fraction and fractional shortening of the patients were significantly decreased compared with those in the control group while heart rate-corrected QT interval was prolonged in the former group. QRS interval was more widened in non-specific MD patients, but without statistical significance.

CONCLUSION

The potentially severe cardiac involvement observed in our subjects suggests that early cardiac evaluation after confirming the diagnosis of MD and regular follow-up tests should be strongly recommended in children even in cases without typical cardiac manifestations.

Cardiac arrest in kearns-sayre syndrome

The prognosis of progressive ophthalmoplegia in patients with large-scale mitochondrial DNA deletions is highly variable and almost unpredictable. The risk to develop cardiac involvement and sudden cardiac death is strikingly high, especially in patients with Kearns-Sayre syndrome (KSS). The most typical cardiac complications of the disease are conduction defects, which usually begin with left anterior fascicular block with or without right bundle branch block (RBBB), progressing sometimes rapidly to complete atrioventricular block. Other cardiac manifestations reported are first or second degree of AV block, QT prolongation, torsades de pointes ventricular tachycardia, and rarely dilated cardiomyopathy. Most frequently syncope, sometimes even sudden cardiac death, is the first clinical sign of the cardiac disease in KSS. Due to these life-threatening cardiac conditions, patients should be carefully monitored for cardiac signs and symptoms and pacemaker implantation should be suggested early to avoid sudden cardiac arrest in KSS.Here, we present two cases of KSS with life-threatening syncope due to complete atrioventricular block. To emphasize the importance of an early pacemaker implantation, we review the literature on cardiac complications in KSS in the last 20 years. In almost all of the reviewed cases, ophthalmoplegia or ptosis was present before the cardiac manifestations. In most of the cases, syncope was the first symptom of the cardiac involvement. There was no correlation between the age of the onset of the disease and the onset of cardiac manifestations.With our current report, we increase awareness for life-threatening cardiac complications in patients with KSS.

Electrocardiography as an early cardiac screening test in children with mitochondrial disease

Purpose

To evaluate myocardial conductivity to understand cardiac involvement in patients with mitochondrial disease.

Methods

We performed retrospective study on fifty-seven nonspecific mitochondrial encephalopathy patients with no clinical cardiac manifestations. The patients were diagnosed with mitochondrial respiratory chain complex defects through biochemical enzyme assays of muscle tissue. We performed standard 12-lead electrocardiography (ECG) on all patients.

Results

ECG abnormalities were observed in 30 patients (52.6%). Prolongation of the QTc interval (>440 ms) was seen in 19 patients (33.3%), widening of the corrected QRS interval in 15 (26.3%), and bundle branch block in four (7.0%). Atrioventricular block, premature atrial contraction and premature ventricular contraction were seen in two patients each (3.5%) and Wolff-Parkinson-White syndrome in one patient (1.8%).

Conclusion

Given this finding, we recommend active screening with ECG in patients with mitochondrial disease even in patients without obvious cardiac manifestation.

Misdiagnosis of long QT syndrome as epilepsy at first presentation

STUDY OBJECTIVE

Long QT syndrome has significant mortality, which is reduced with appropriate management. It is known that long QT syndrome masquerades as other conditions, including seizure disorders. We aim to evaluate a series of patients with genetically confirmed long QT syndrome to establish the frequency of delayed recognition. We also examine causes and potential consequences of diagnostic delay.

METHODS

A consecutive case series of patients with long QT syndrome was identified through the Cardiac Inherited Disease Registry in New Zealand between 2000 and 2005. Detailed retrospective review of 31 cases was undertaken. The primary outcome was the time from first presentation with sudden loss of consciousness to a diagnosis of long QT syndrome. If the diagnosis was not made at the initial presentation, it was considered delayed. For the patients with a delayed diagnosis, the median duration of delay was compared between the subgroup of patients initially misdiagnosed with epilepsy and the others.

RESULTS

Genetic mutations in 31 probands were consistent with long QT type 1 in 18 (58%) patients, long QT type 2 in 10 (32%) and long QT type 3 in 3 (10%). Median age at diagnosis was 21 years (1 day to 54 years). Thirteen patients (39%) experienced diagnostic delay after presentation with syncope or seizure: median delay 2.4 years (2 months to 23 years). Electroencephalograms were obtained in 10 patients; 5 were diagnosed with epilepsy. For those labeled epileptic, diagnostic delay was significantly longer than with other misdiagnoses: estimated median difference 9.75 years (95% confidence interval 7.6 to 20.7 years). During the delay period, 4 sudden unexplained deaths reportedly occurred in young relatives. Ten of the 13 had an ECG before diagnosis, with unrecognized pulse rate-corrected QT interval prolongation in 8 cases (range 0.47 to 0.65 seconds).

CONCLUSION

Delayed diagnosis of long QT syndrome is frequent. Symptoms are often attributed to alternative diagnoses, most commonly seizure disorder. Patients labeled as epileptic experience a particularly long diagnostic delay. ECGs were frequently requested, but interpretation errors were common. Given the potentially preventable mortality of long QT syndrome, emergency physicians investigating syncope and seizure should maintain a high index of suspicion.