Long QT syndrome patients may faint due to neurocardiogenic syncope

Congenital Long QT Syndrome

Congenital long QT syndrome (LQTS) encompasses a group of heritable conditions that are associated with cardiac repolarization dysfunction. Since its initial description in 1957, our understanding of LQTS has increased dramatically. The prevalence of LQTS is estimated to be ∼1:2,000, with a slight female predominance. The diagnosis of LQTS is based on clinical, electrocardiogram, and genetic factors. Risk stratification of patients with LQTS aims to identify those who are at increased risk of cardiac arrest or sudden cardiac death. Factors including age, sex, QTc interval, and genetic background all contribute to current risk stratification paradigms. The management of LQTS involves conservative measures such as the avoidance of QT-prolonging drugs, pharmacologic measures with nonselective β-blockers, and interventional approaches such as device therapy or left cardiac sympathetic denervation. In general, most forms of exercise are considered safe in adequately treated patients, and implantable cardioverter-defibrillator therapy is reserved for those at the highest risk. This review summarizes our current understanding of LQTS and provides clinicians with a practical approach to diagnosis and management.

Prolongation of Electrocardiographic T Wave Parameters Recorded during the Head-Up Tilt Table Test as Independent Markers of Syncope Severity in Children

The head-up tilt table test (HUTT) with the upright phase is used to help determine an imbalance of the sympathetic nervous system that is related to abnormal electrocardiographic repolarization in children with vasovagal syncope (VVS) and also in patients with the long QT syndrome (LQTS). The study attempted to evaluate T wave morphology and QT and TpTe (Tpeak-Tend) intervals recorded in ECG during the HUTT for a more accurate diagnosis of children with VVS. The group investigated 70 children with a negative HUTT result: 40 patients with VVS and 30 healthy volunteers without syncope. The RR interval as well as TpTe, and QTc intervals were measured in lead V5 of electrocardiogram (ECG) on admission to the hospital and during three phases of the HUTT. In syncopal children, which included 23 children with bifid or flat T waves and 17 patients with normal T waves in the upright phase, the QTc and TpTe were longer (p < 0.001) compared to the other test phases and longer (p < 0.001) than in the control group, respectively, with the risk of arrhythmias. Only in the control group, the TpTe was shorter (p < 0.001) in the upright phase than in the other tilt phases. The TpTe in the upright phase (>70 ms) was a good discriminator, and was better than the QTc (>427 ms). Prolongation of electrocardiographic TpTe and QT intervals, in addition to the (abnormal T wave morphology recorded during the HUTT, are helpful for identifying VVS children more predisposed to ventricular arrhythmias with a latent risk of LQTS. Further studies are required to assess the value of these repolarization parameters in clinical practice.

Coexistence of congenital long QT syndrome and autonomic dysregulation in children

Loss of consciousness (LOC) in long QT syndrome (LQTS) patients can be caused by torsade de pointes (TdP) or vasovagal syncope (VVS). On genetic testing and head-up tilt testing (HUTT), we diagnosed three young patients with both genotyped LQTS and autonomic dysregulation. According to grade of prolongation of QT interval and LOC status, syncope episodes in two patients were classified as due to VVS, while those of the other patient were due to TdP. We also diagnosed one patient with postural orthostatic tachycardia syndrome. Syncope in LQTS patients should not automatically be labeled TdP. If there is a possibility of VVS, HUTT should be performed, but careful observation is required because TdP cannot be completely ruled out.

Syncope in Hereditary Arrhythmogenic Syndromes

Since the discovery of the first mutation causing long QT syndrome (LQTS) in 1995, the field of hereditary arrhythmogenic syndromes has expanded greatly. Today, these syndromes include LQTS, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and short QT syndrome. There is also evidence suggesting that the newly described malignant early repolarization syndrome also has a genetic cause.

Syncope in genotype-negative long QT syndrome family members

Unaffected long-QT syndrome family members (FMs) frequently experience syncope. The aims of this study were to test the hypothesis that syncope events in FMs are benign events and to compare clinical characteristics, triggers eliciting the syncope events, and long-term outcomes between FMs and those with LQT1 or LQT2 mutations from the international Long QT Syndrome Registry. A total of 679 FMs, 864 LQT1 patients, and 782 LQT2 patients were included. Seventy-eight FMs (11%) experienced cardiovascular events. Almost all cardiovascular events were nonfatal syncope; only 1 FM, with an additional mitral valve prolapse, experienced aborted cardiac arrest during exercise. The mean age at first syncope in FMs was 17 years, and female FMs experienced syncope more frequently than male FMs (14% vs 9%, p = 0.027). Syncope was more frequently triggered by exercise in LQT1 patients (43% in LQT1 patients vs 5% in FMs, p <0.001), while syncope triggered by a variety of other triggers was more frequent in FMs (54% in FMs vs 22% in LQT1 patients and 30% in LQT2 patients, p <0.001 for both). None of the FMs experienced aborted cardiac arrest or sudden cardiac death after the first syncopal episode. In conclusion, syncope is frequently present in FMs, and these syncopal events occurred more frequently in female than in male FMs, with an increased incidence in midadolescence. Triggers eliciting the syncopal events were different between FMs and patients with long-QT syndrome mutations. Hence, the type of trigger is useful in distinguishing between high- and low-risk syncope. These data indicate that FMs from families with LQTS have a benign form of syncope, most likely related to vasovagal syncope and not ventricular tachyarrhythmic syncope.

Genetic aspects of vasovagal syncope: a systematic review of current evidence

Knowledge on the aetiology of vasovagal syncope (VVS) is of great importance to optimize its diagnostic and therapeutic options. To unravel the largely unknown pathophysiology, studies on genetic aspects of VVS can be of use. This systematic review on all available literature aims to provide an overview of the current knowledge of VVS genetics. The MEDLINE and EMBASE database were systematically searched for all studies discussing genetic factors as a cause of VVS. Hereditary aspects of VVS were studied in 19 studies. Six studies determined a positive family history in, respectively, 19-90% of the VVS patients. These numbers, however, are not higher than the cumulative incidence of VVS in the general population (35-39%). Four studies examined potential genetic polymorphisms associated with VVS. Only a Gly389 allele was more frequently present in VVS patients with a positive HUT test, although the significance level was set much higher than usual in genetic studies, and this result has not been replicated so far. Knowledge on genetic aspects of VVS could be very useful in clinical practice and research, but the current evidence that it has a genetic basis is not very strong.

Syncope and QT prolongation among patients treated with methadone for heroin dependence in the city of Copenhagen

BACKGROUND

Methadone is prescribed to heroin addicts to decrease illicit opioid use. Prolongation of the QT interval in the ECG of patients with torsade de pointes (TdP) has been reported in methadone users. As heroin addicts sometimes faint while using illicit drugs, doctors might attribute too many episodes of syncope to illicit drug use and thereby underestimate the incidence of TdP in this special population, and the high mortality in this population may, in part, be caused by the proarrhythmic effect of methadone.

METHODS

In this cross-sectional study interview, ECGs and blood samples were collected in a population of adult heroin addicts treated with methadone or buprenorphine on a daily basis. Of the patients at the Drug Addiction Service in the municipal of Copenhagen, 450 (approximately 52%) were included. The QT interval was estimated from 12 lead ECGs. All participants were interviewed about any experience of syncope. The association between opioid dose and QT, and methadone dose and reporting of syncope was assessed using multivariate linear regression and logistic regression, respectively.

RESULTS

Methadone dose was associated with longer QT interval of 0.140 ms/mg (p = 0.002). No association between buprenorphine and QTc was found. Among the subjects treated with methadone, 28% men and 32% women had prolonged QTc interval. None of the subjects treated with buprenorphine had QTc interval >0.440 s((1/2)). A 50 mg higher methadone dose was associated with a 1.2 (95% CI 1.1 to 1.4) times higher odds for syncope.

CONCLUSIONS

Methadone is associated with QT prolongation and higher reporting of syncope in a population of heroin addicts.

Impedance cardiography and beat-to-beat blood pressure monitoring in diagnosis of syncope in long-QT syndrome

Syncope represents a diagnostic challenge in patients affected by long-QT syndrome (LQTS). It is crucial for the therapeutic decision to distinguish between potentially life-threatening ventricular tachycardias (Torsadede-pointes) and-especially during adolescence-neurocardiogenic syncopes. This case report presents a patient with LQTS2 (mutation in the HERG gene) on medication with beta-blocker, in whom a head-up-tilt table test was performed after syncope of unknown origin. The test was chosen in order to reproduce the circumstances under which the syncope had happened. The monitoring device consisted of impedance cardiography as well as non-invasive beat-to-beat blood-pressure measurement. By these means it was possible to register a reduced peripheral vascular resistance after tilting the patient, a reduced cardiac output and bradycardia leading to syncope after four minutes of upright posture. This was suggestive for neurocardiogenic syncope as a cause for the spell experienced. Further non-invasive diagnostic methods were normal. As the patient's family history was negative for syncopes, Torsade-de-pointes seemed unlikely.In this special case the non-invasive monitoring system of cardiac output, peripheral vascular resistance and beat-to-beat blood pressure measurements was useful as a supplemental tool during evaluation of syncope and helpful in decision-making against implantation of an ICD and for a more intense treatment with betablockers. Such monitoring devices offer new insights into the orthostatic regulation in young patients.