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

Utilizing median and maximum QTc values improves prediction of breakthrough cardiac events in pediatric long QT syndrome

INTRODUCTION

Although prior studies indicate that a QTc > 500 ms on a single baseline 12-lead electrocardiogram (ECG) is associated with significantly increased risk of arrhythmic events in long QT syndrome (LQTS), less is known about the risk of persistent QT prolongation. We sought to determine QTc persistence and its prognostic effect on breakthrough cardiac events (BCEs) among pediatric patients treated for LQTS.

METHODS

We performed a retrospective analysis of 433 patients with LQTS evaluated, risk-stratified, and undergoing active guideline-based LQTS treatment between 1999 and 2019. BCEs were defined as arrhythmogenic syncope/seizure, sudden cardiac arrest (SCA), appropriate VF-terminating ICD shock, and sudden cardiac death (SCD).

RESULTS

During the median follow-up of 5.5 years (interquartile range [IQR] = 3-9), 32 (7%) patients experienced a total of 129 BCEs. A maximum QTc threshold of 520 ms and median QTc threshold of 490 ms were determined to be strong predictors for BCEs. A landmark analysis controlling for age, sex, genotype, and symptomatic status demonstrated models utilizing both the median QTc and maximum QTc demonstrated the highest discriminatory value (c-statistic = 0.93-0.95). Patients in the high-risk group (median QTc > 490 ms and maximum QTc > 520 ms) had a significantly lower BCE free survival (70%-81%) when compared to patients in both medium-risk (93%-97%) and low-risk (98%-99%) groups.

CONCLUSIONS

The risk of BCE among patients treated for LQTS increases not only based upon their maximum QTc, but also their median QTc (persistence of QTc prolongation). Patients with a maximum QTc > 520 ms and median QTc > 490 ms over serial 12-lead ECGs are at the highest risk of BCE while on guideline-directed medical therapy.

Individualized QT interval (QTi) is a powerful diagnostic tool in long QT syndrome: results from a large validation study

Aims

Diagnosis of Long QT syndrome (LQTS) is based on prolongation of the QT interval corrected for heart rate (QTc) on surface ECG and genotyping. However, up to 25% of genotype positive patients have a normal QTc interval. We recently showed that individualized QT interval (QTi) derived from 24 h holter data and defined as the QT value at the intersection of an RR interval of 1,000 ms with the linear regression line fitted through QT-RR data points of each individual patient was superior over QTc to predict mutation status in LQTS families. This study aimed to confirm the diagnostic value of QTi, fine-tune its cut-off value and evaluate intra-individual variability in patients with LQTS.

Methods

From the Telemetric and Holter ECG Warehouse, 201 recordings from control individuals and 393 recordings from 254 LQTS patients were analysed. Cut-off values were obtained from ROC curves and validated against an in house LQTS and control cohort.

Results

ROC curves indicated very good discrimination between controls and LQTS patients with QTi, both in females (AUC 0.96) and males (AUC 0.97). Using a gender dependent cut-off of 445 ms in females and 430 ms in males, a sensitivity of 88% and specificity of 96% were achieved, which was confirmed in the validation cohort. No significant intra-individual variability in QTi was observed in 76 LQTS patients for whom at least two holter recordings were available (483 ± 36 ms vs. 489 ± 42 ms, p = 0.11).

Conclusions

This study confirms our initial findings and supports the use of QTi in the evaluation of LQTS families. Using the novel gender dependent cut-off values, a high diagnostic accuracy was achieved.

Value of screening for the risk of sudden cardiac death in young competitive athletes

AIMS

This study aimed to report the long-term findings of the Italian programme of cardiovascular preparticipation screening (PPS) in young, competitive athletes.

METHODS AND RESULTS

The study assessed the diagnostic yield for diseases at risk of sudden cardiac death (SCD), the costs of serial evaluations, and the long-term outcomes of PPS in a large population of Italian children (age range, 7-18 years). The PPS was repeated annually and included medical history, physical examination, resting electrocardiogram, and stress testing; additional tests were reserved for athletes with abnormal findings. Over an 11-year study period, 22 324 consecutive children [62% males; mean age, 12 (interquartile range, 10-14) years at first screening] underwent a total of 65 397 annual evaluations (median 2.9/child). Cardiovascular diseases at risk of SCD were identified in 69 children (0.3%) and included congenital heart diseases (n = 17), channelopathies (n = 14), cardiomyopathies (n = 15), non-ischaemic left ventricular scar with ventricular arrhythmias (n = 18), and others (n = 5). At-risk cardiovascular diseases were identified over the entire age range and more frequently in children ≥12 years old (n = 63, 91%) and on repeat evaluation (n = 44, 64%). The estimated cost per diagnosis was 73 312€. During a follow-up of 7.5 ± 3.7 years, one child with normal PPS findings experienced an episode of resuscitated cardiac arrest during sports activity (event rate of 0.6/100.000 athletes/year).

CONCLUSION

The PPS programme led to the identification of cardiovascular diseases at risk of SCD over the whole study age range of children and more often on repeat evaluations. Among screened children, the incidence of sport-related cardiac arrest during long-term follow-up was low.

ECG as a risk stratification tool in patients with wearable cardioverter-defibrillator

BACKGROUND

The wearable cardioverter defibrillator (WCD) is increasingly used in patients at elevated risk for ventricular arrhythmias but not fulfilling the indications for an implantable cardioverter defibrillator (ICD). Currently, there is an insufficient risk prediction of fatal arrhythmias in patients at risk. In this study, we assessed the prognostic role of baseline electrocardiogram (ECG) in WCD patients.

METHODS

WCD patients from diverse clinical institutions in Germany (n = 227) were retrospectively enrolled and investigated for the incidences of death or ventricular arrhythmias during WCD wearing. In addition, the widely accepted ECG predictors of adverse outcome were analyzed in patients with arrhythmic events.

RESULTS

Life-threatening arrhythmias occurred in 22 (9.7 %) patients, mostly in subjects with ischemic heart disease (15 of 22). There was no difference in baseline left ventricular ejection fraction (LVEF) in subjects with and without arrhythmic events (31.3 ± 7.9 % vs. 32.6 ± 8.3 %; p = 0,24). Patients with arrhythmia exhibited significantly longer QRS duration (109.5 ± 23.1 ms vs. 100.6 ± 22.3 ms, p = 0,04), Tpeak-Tend (Tp-e) (103.1 ± 15.6 ms vs. 93.2 ± 19.2 ms, p = 0,01) and QTc (475.0 ± 60.0 ms vs. 429.6 ± 59.4 ms, p < 0,001) intervals. In contrast, no significant differences were found for incidences of fragmented QRS (27.3 % vs. 24 %, p = 0.79) and inverted/biphasic T-waves (16.6 % vs. 22.7 %, p = 0,55). In multivariate regression analysis both Tp-e (HR 1.03; 95 % CI 1.001-1.057; p = 0.02) and QTc (HR 1.02; 95 % CI 1.006-1.026; p < 0.001) were identified as independent predictors of ventricular arrhythmias. After WCD use, the prophylactic ICD was indicated in 76 patients (33 %) with uneventful clinical course but persistent LVEF ≤35 %. The ECG analysis in these subjects did not reveal any relevant changes in arrhythmogenesis markers.

CONCLUSIONS

ECG repolarization markers Tp-e and QTc are associated with malignant arrhythmias in WCD patients and may be used - in addition to other established risk markers - to identify appropriate patients for ICD implantation.

Holter Recordings at Initial Assessment for Long QT Syndrome: Relationship to Genotype Status and Cardiac Events

Background: The relationship of Holter recordings of repolarization length to outcome in long QT syndrome (LQTS) is unknown. Methods: Holter recordings and initial 12 lead ECG QTc were related to outcome in 101 individuals with LQTS and 28 gene-negative relatives. Mean QTc (mQTc) and mean RTPc (R-wave to peak T-wave, mRTPc) using Bazett correction were measured, analyzing heart rates 40 to 120 bpm. Previously reported upper limit of normal (ULN) were: women and children (<15 years), mQTc 454, mRTPc 318 ms; men mQTc 446 ms, mRTPc 314 ms. Results: Measurements in LQTS patients were greatly prolonged; children and women mean mQTc 482 ms (range 406−558), mRTPc 351 ms (259−443); males > 15 years mQTc 469 ms (407−531), mRTPc 338 ms (288−388). Ten patients had cardiac arrest (CA), and 24 had arrhythmic syncope before or after the Holter. Holter values were more closely related to genotype status and symptoms than 12 lead QTc, e.g., sensitivity/specificity for genotype positive status, mRTPc > ULN (89%/86%); CA, mRTPc > 30 ms over ULN (48%/100%). Of 34 symptomatic (CA/syncope) patients, only 9 (26%) had 12 lead QTc > 500 ms, whereas 33/34 (94%) had an mRTPc or mQTc above ULN. In 10 with CA, all Holter measurements were > 15 ms above ULN, but only two had 12 lead QTc > 500 m. Conclusions: Holter average repolarization length, particularly mRTPc, reflects definite LQTS status and clinical risk better than the initial 12 lead QTc. Values below ULN indicate both a low risk of having LQTS and a low risk of cardiac events in the small percentage that do.

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.

Performance of Automated Telemetry in Diagnosing QT Prolongation in Critically Ill Patients

BACKGROUND

QT prolongation increases the risk of ventricular arrhythmia and is common among critically ill patients. The gold standard for QT measurement is electrocardiography. Automated measurement of corrected QT (QTc) by cardiac telemetry has been developed, but this method has not been compared with electrocardiography in critically ill patients.

OBJECTIVE

To compare the diagnostic performance of QTc values obtained with cardiac telemetry versus electrocardiography.

METHODS

This prospective observational study included patients admitted to intensive care who had an electrocardiogram ordered simultaneously with cardiac telemetry. Demographic data and QTc determined by electrocardiography and telemetry were recorded. Bland-Altman analysis was done, and correlation coefficient and receiver operating characteristic (ROC) coefficient were calculated.

RESULTS

Fifty-one data points were obtained from 43 patients (65% men). Bland-Altman analysis revealed poor agreement between telemetry and electrocardiography and evidence of fixed and proportional bias. Area under the ROC curve for QTc determined by telemetry was 0.9 (P < .001) for a definition of prolonged QT as QTc ≥ 450 milliseconds in electrocardiography (sensitivity, 88.89%; specificity, 83.33%; cutoff of 464 milliseconds used). Correlation between the 2 methods was only moderate (r = 0.6, P < .001).

CONCLUSIONS

QTc determination by telemetry has poor agreement and moderate correlation with electrocardiography. However, telemetry has an acceptable area under the curve in ROC analysis with tolerable sensitivity and specificity depending on the cutoff used to define prolonged QT. Cardiac telemetry should be used with caution in critically ill patients.

QT interval dynamics and triggers for QT prolongation immediately following cardiac arrest

BACKGROUND

The prolongation in QT interval typically observed following cardiac arrest is considered to be multifactorial and induced by external triggers such as hypothermia therapy and exposure to antiarrhythmic medications.

OBJECTIVE

To evaluate the corrected QT interval (QTc) dynamics in the first 10 days following cardiac arrest with respect to the etiology of arrest, hypothermia and QT prolonging medications.

METHODS

We enrolled 104 adult survivors of cardiac arrest, where daily ECG was available for at least 3 days. We followed their QT and QRS intervals for the first 10 days of hospitalization. We used both Bazett and Fridericia formulas to correct for heart rate. For patients with QRS < 120 we analyzed the QTc interval (n = 90) and for patients with QRS > 120 ms we analyzed the JTc (n = 104) vs. including only the narrow QRS samples (n = 89). We stratified patients by 3 groups: (1) presence of ischemic heart disease (IHD) (2) treatment with hypothermia protocol, and (3) treatment with QTc prolonging medications. Additionally, genetic information obtained during hospitalization was analyzed.

RESULTS

QTc and JTc intervals were significantly prolonged in the first 6 days. Maximal QTc/JTc prolongation was observed in day 2 (QTcB = 497 ± 55). There were no differences in daily QTc/JTc and QRS intervals in the first 2 days post arrest between patients with or without hypothermia induction but such difference was found with QT prolonging medications. All subgroups demonstrated significantly prolonged QTc/JTc interval regardless of the presence of IHD, hypothermia protocol or QTc prolonging medication exposure. Our results were consistent for both Bazetts' and Frediricia correction and for any QRS duration. Prolongation of the JTcB beyond 382 ms after day 3 predicted sustained QTc/JTc prolongation beyond day 6 with an ROC of 0.78.

CONCLUSIONS

QTc/JTc interval is significantly and independently prolonged post SCA, regardless of known QT prolonging triggers. Normalization of the QTc post cardiac arrest should be expected only after day 6 of hospitalization. Assessment of the QTc for adjudication of the etiology of arrest or for monitoring the effect of QT prolonging medications may be unreliable.

QT correction using Bazett's formula remains preferable in long QT syndrome type 1 and 2

Background

The heart rate (HR) corrected QT interval (QTc) is crucial for diagnosis and risk stratification in the long QT syndrome (LQTS). Although its use has been questioned in some contexts, Bazett's formula has been applied in most diagnostic and prognostic studies in LQTS patients. However, studies on which formula eliminates the inverse relation between QT and HR are lacking in LQTS patients.

We therefore determined which QT correction formula is most appropriate in LQTS patients including the effect of beta blocker therapy and an evaluation of the agreement of the formulae when applying specific QTc limits for diagnostic and prognostic purposes.

Methods

Automated measurements from routine 12‐lead ECGs from 200 genetically confirmed LQTS patients from two Swedish regions were included (167 LQT1, 33 LQT2). QT correction was performed using the Bazett, Framingham, Fridericia, and Hodges formulae. Linear regression was used to compare the formulae in all patients, and before and after the initiation of beta blocking therapy in a subgroup (n = 44). Concordance analysis was performed for QTc ≥ 480 ms (diagnosis) and ≥500 ms (prognosis).

Results

The median age was 32 years (range 0.1–78), 123 (62%) were female and 52 (26%) were children ≤16 years. Bazett's formula was the only method resulting in a QTc without relation with HR. Initiation of beta blocking therapy did not alter the result. Concordance analyses showed clinically significant differences (Cohen's kappa 0.629–0.469) for diagnosis and prognosis in individual patients.

Conclusion

Bazett's formula remains preferable for diagnosis and prognosis in LQT1 and 2 patients.

QT interval greater than 460 ms in multiple electrocardiograms during follow-up in patients with Brugada syndrome: What does it contribute?

INTRODUCTION

Corrected QT interval (QTc) >460 ms in the right precordial leads has been described as a predictor of malignant ventricular arrhythmias (MVA) in patients with Brugada syndrome (BrS).

OBJECTIVE

To assess the presence of QTc>460 ms in multiple electrocardiograms (ECGs) during follow-up as a predictor of recurrence of MVA in patients with BrS.

METHODS

The study group included 43 patients with BrS and an implantable cardioverter-defibrillator. ECGs were performed serially between June 2000 and January 2017. QT interval was measured and QTc was obtained by Bazett's formula. The sample was divided into three groups: Group 1 (patients with no ECGs with QTc>460 ms); Group 2 (patients with only one ECG with QTc>460 ms); and Group 3 (patients with two or more ECGs with QTc>460 ms).

RESULTS

The following variables were more frequently observed in Group 3: family history of sudden death (p=0.023), previous history of cardiorespiratory arrest (p=0.032), syncope (p=0.039), documented MVA (p=0.002), and proportion of ECGs with coved-type ST interval during follow-up (p=0.002). In Group 3, 67% of BrS patients had events during follow-up, as opposed to only 22% of Group 1 and 14% of Group 2 (Group 1 vs. Group 2, p=0.33015; Group 1 vs. Group 3, p=0.04295; and Group 2 vs. Group 3, p=0.04155).

CONCLUSIONS

QTc>460 ms in more than one ECG during follow-up increases the risk of MVA events in patients with BrS.

Atrial Fibrillation in Long QT Syndrome by Genotype

BACKGROUND

Long QT syndrome (LQTS) is caused by the abnormal function of ion channels, which may also affect atrial electrophysiology and be associated with the risk of atrial fibrillation (AF). However, large-scale studies of AF risk among patients with LQTS and its relation to LQTS manifestations are lacking. We aimed to assess the risk of AF and its relationship to the LQTS genotype and the long-term prognosis in patients with LQTS.

METHODS

Genotype-positive patients with LQTS (784 LQT1, 746 LQT2, and 233 LQT3) were compared with 2043 genotype-negative family members. Information on the occurrence of AF was based on physician-reported ECG-verified events. Multivariate Cox proportional hazards regression analyses were performed for ages 0 to 60 and after 60 years (reflecting an early and late-onset of AF) to assess the risk of incident AF by genotype and the relationship of AF to the risk of cardiac events defined as syncope, documented torsades de pointes, and aborted cardiac arrest or sudden cardiac death.

RESULTS

In patients followed from birth to 60 years of age, patients with LQT3 had an increased risk of AF compared with genotype-negative family members (hazard ratio=6.62; 95% CI, 2.04-21.49; P<0.001), while neither LQT1 nor LQT2 demonstrated increased AF risk. After the age of 60 years, patients with LQT2 had significantly lower risk of AF compared with genotype-negative controls (hazard ratio=0.07; 95% CI, 0.01-0.53, P=0.011). AF was a significant predictor of cardiac events in patients with LQT3 through the age of 60 (hazard ratio=5.38; 95% CI, 1.17-24.82; P=0.031).

CONCLUSIONS

Our data demonstrate an increased risk of early age AF in patients with LQT3 and also indicate a protective effect of the LQT2 genotype in it's association with a decreased risk of AF after the age of 60.

Quantitative T-wave morphology assessment from surface ECG is linked with cardiac events risk in genotype-positive KCNH2 mutation carriers with normal QTc values

INTRODUCTION

Long QT syndrome (LQTS) mutation carriers have elevated the risk of cardiac events even in the absence of QTc prolongation; however, mutation penetrance in patients with normal QTc may be reflected in abnormal T-wave shape, particularly in KCNH2 mutation carriers. We aimed to assess whether the magnitude of a three-dimensional T-wave vector (TwVM) will identify KCNH2-mutation carriers with normal QTc at risk for cardiac events.

METHODS

Adult LQT2 patients with QTc < 460 ms in men and <470 ms in women (n = 113, age 42 ± 16 years, 43% male) were compared with genotype-negative family members (n = 1007). The TwVM was calculated using T-wave amplitudes in leads V6, II, and V2 as the square root of (TV6²  + TII²  + (0.5*TV2)² ). Cox regression analysis adjusted for gender and time-dependent beta-blocker use was performed to assess cardiac event (CE) risk, defined as syncope, aborted cardiac arrest, implantable cardioverter-defibrillator therapy, or sudden death.

RESULTS

Dichotomized by median of 0.30 mV, lower TwVM was associated with elevated CE risk compared to those with high TwVM (HR = 2.95, 95% CI, 1.25-6.98, P = .014) and also remained significant after including sex and time-dependent beta-blocker usage in the Cox regression analysis (HR = 2.64, 95% CI, 1.64-4.24, P < .001). However, these associations were found only in women but not in men who had low event rates.

CONCLUSION

T-wave morphology quantified as repolarization vector magnitude using T-wave amplitudes retrieved from standard 12-lead electrocardiogram predicts cardiac events risk in LQT2 women and appears useful for risk stratification of KCNH2-mutation carriers without QTc prolongation.

Risk Stratification of Type 2 Long-QT Syndrome Mutation Carriers With Normal QTc Interval: The Value of Sex, T-Wave Morphology, and Mutation Type

BACKGROUND

Long-QT (LQT) syndrome mutation carriers have higher risk of cardiac events than unaffected family members even in the absence of QTc prolongation. Changes in T-wave morphology may reflect penetrance of LQT syndrome mutations. We aimed to assess whether T-wave morphology may improve risk stratification of LQT2 mutation carriers with normal QTc interval.

METHODS

LQT2 mutation carriers with QTc <460 ms in men and <470 ms in women (n=154) were compared with unaffected family members (n=1007). Baseline ECGs recorded at age ≥18 years underwent blinded assessment. Flat, notched, or negative T waves in leads II or V₅ were considered abnormal. Cox regression analysis was performed to assess the association between T-wave morphology, the presence of mutations in the pore region of KCNH2, and the risk of cardiac events defined as syncope, aborted cardiac arrest, defibrillator therapy, or sudden cardiac death. Sex-specific associations were estimated using interactions terms.

RESULTS

LQT2 female carriers with abnormal T-wave morphology had significantly higher risk of cardiac events compared with LQT2 female carriers with normal T waves (hazard ratio, 3.31; 95% confidence interval, 1.68-6.52; P=0.001), whereas this association was not significant in men. LQT2 men with pore location of mutations have significantly higher risk of cardiac events than those with nonpore mutations (hazard ratio, 6.01; 95% confidence interval, 1.50-24.08; P=0.011), whereas no such association was found in women.

CONCLUSIONS

The risk of cardiac events in LQT2 carriers with normal QTc is associated with abnormal T-wave morphology in women and pore location of mutation in men. The findings further indicate sex-specific differences in phenotype and genotype relationship in LQT2 patients.

Primary prevention with the implantable cardioverter-defibrillator in high-risk long-QT syndrome patients

AIMS

Prospective data regarding the role of implantable cardioverter-defibrillator (ICD) for the primary prevention of sudden cardiac death in patients with long QT syndrome (LQTS) is scarce. Herein, we explore the prospective Rochester LQTS ICD registry to assess the risk for appropriate shock in primary prevention in a real-world setting.

METHODS AND RESULTS

We studied 212 LQTS patients that had ICD implantation for primary prevention. Best-subsets proportional-hazards regression analysis was used to identify clinical variables that were associated with the first appropriate shock. Conditional models of Prentice, Williams, and Peterson were utilized for the analysis of recurrent appropriate shocks. During a median follow-up of 9.2 ± 4.9 years, there were 42 patients who experienced at least one appropriate shock and the cumulative probability of appropriate shock at 8 years was 22%. QTc ≥ 550 ms [hazard ratio (HR) 3.94, confidence interval (CI) 2.08-7.46; P < 0.001) and prior syncope on β-blockers (HR 1.92, CI 1.01-3.65; P = 0.047) were associated with increased risk of appropriate shock. History of syncope while on β-blocker treatment (HR 1.87, CI 1.28-2.72; P = 0.001), QTc 500-549 ms (HR 1.68, CI 1.10-2.81; P = 0.048), and QTc ≥ 550 ms (HR 3.66, CI 2.34-5.72; P < 0.001) were associated with increased risk for recurrent appropriate shocks, while β-blockers were not protective (HR 1.03, CI 0.63-1.68, P = 0.917). LQT2 (HR 2.10, CI 1.22-3.61; P = 0.008) and multiple mutations (HR 2.87, CI 1.49-5.53; P = 0.002) were associated with higher risk for recurrent shocks as compared with LQT1.

CONCLUSION

In this prospective ICD registry, we identified clinical and genetic variables that were associated appropriate shock risk. These data can be used for risk stratification in high-risk patients evaluated for primary prevention with ICD.

Incidence and outcomes of long QTc in acute medical admissions

AIMS

Prolonged QT interval on electrocardiogram (ECG) increases the risk of ventricular arrhythmia. Patients admitted to acute medical units (AMU) may be at risk of QT prolongation from multiple, recognised risk factors. Few data exist regarding incidence or outcomes of QT prolongation in acute general medical admissions. The aims were to determine the incidence of Bazett's-corrected QT (QTc) prolongation upon admission to AMU; the relationship between QTc and inpatient mortality, length of stay and readmission; proportion with prolonged QTc subsequently administered QT interval-prolonging drugs.

METHODS

Retrospective, observational study of 1000 consecutive patients admitted to an AMU in a large urban hospital.

EXCLUSION CRITERIA

age <18 years, ventricular pacing, poor quality/absent ECG. QTc determined manually from ECG obtained within 4-hours of admission. QTc prolongation considered ≥470 milliseconds (males) and ≥480 milliseconds (females). In both genders, >500 milliseconds was considered severe. Study end-points, (a) incidence of QTc prolongation at admission; (b) inpatient mortality, length of stay and readmission rates; (c) proportion with QTc prolongation subsequently administered QT interval-prolonging drugs.

RESULTS

Of 1000 patients, 288 patients were excluded, therefore final sample was n = 712. Patient age (mean ± SD) was 63.1 ± 19.4 years; females 49%. QTc prolongation was present in n = 50 (7%) at admission; 1.7% had QTc interval >500 ms. Of the 50 patients admitted with prolonged QTc, 6 (12%) were subsequently administered QT interval-prolonging drugs. QTc prolongation was not associated with worse inpatient mortality or readmission rate. Length of stay was greater in those with prolonged QTc, 7.2 (IQR 2.4-13.2) days vs 3.3 (IQR 1.3-10.0; P = 0.004), however, in a regression model, presence of QTc did not independently affect length of stay.

CONCLUSIONS

QTc interval prolongation is frequent among patients admitted to AMU. QT interval-prolonging drugs are commonly prescribed to patients presenting with prolonged QTc but whether this affects clinical outcomes is uncertain.

Assessment of the QT Interval in Athletes: Red Flags and Pitfalls

PURPOSE OF REVIEW

Pre-participation athlete screening has led to the referral of asymptomatic athletes with a prolonged QT interval warranting their evaluation for long QT syndrome (LQTS). Establishing a diagnosis of LQTS can be difficult, particularly in asymptomatic athletes presenting with a prolonged QTc < 500 ms. This review examines the evaluatory pathway to ascertain the common pitfalls leading to mis- or overdiagnosis. We discuss the advanced ECG-based tools and consider their application in the diagnostic process.

RECENT FINDINGS

Critical analysis of the ECG, symptom, and pedigree analysis has established value but relies on experienced interpretation. Protocolisation of the former has effectively reduced error. Exercise recovery ECG testing has demonstrated diagnostic value and provocation testing, reliant on QT hysteresis in LQTS, have shown reasonable sensitivity. Although it is becoming more established in experienced centres, its diagnostic value relies on effective risk stratification and subject selection. LQTS is a rare condition and the precision of any available test is greatly diluted if pre-test probability is low. Clinical and familial evaluation and exercise ECG testing are the foundation of the evaluatory process following referral. Adjunctive tests may have high sensitivity for LQTS but rely on high pre-test probability. Several pitfalls have been identified that can lead to misdiagnosis and thus informed evaluation at an experienced specialist centre is appropriate.

Systematic ajmaline challenge in patients with long QT 3 syndrome caused by the most common mutation: a multicentre study

Aims

Overlap syndromes of long QT 3 syndrome (LQT3) and the Brugada syndrome (BrS) have been reported. Identification of patients with an overlapping phenotype is crucial before initiation of Class I antiarrhythmic drugs for LQT3. Aim of the present study was to elucidate the yield of ajmaline challenge in unmasking the Brugada phenotype in patients with LQT3 caused by the most common mutation, SCN5A-E1784K.

Methods and results

Consecutive families in tertiary referral centres diagnosed with LQT3 caused by SCN5A-E1784K were included in the study. Besides routine clinical work-up, ajmaline challenge was performed after informed consent. A total of 23 subjects (11 female, mean age 27 ± 14 years) from 4 unrelated families with a family history of sudden cardiac death and familial diagnosis of the SCN5A-E1784K mutation underwent ajmaline challenge and genetic testing. Sixteen subjects (9 female) were found to be heterozygous carriers of SCN5A-E1784K. Ajmaline challenge was positive in 12 out of the 16 (75%) mutation carriers, but negative in all non-carriers. Following ajmaline, a significant shortening of the rate-corrected JT (JTc) interval was observed in mutation carriers. The baseline JTc interval was significantly longer in mutation carriers with a positive ajmaline challenge compared with those with a negative one.

Conclusion

Overlap of LQT3 and BrS in patients carrying the most common mutation is high. Therefore, ajmaline challenge represents an important step to rule out potential BrS overlap in these patients before starting sodium channel blockers for the beneficial effect of QT shortening in LQT3.

QTc prolongation in short-term treatment of schizophrenia patients: effects of different antipsychotics and genetic factors

Antipsychotics are effective in treating schizophrenia but may lead to a higher cardiovascular risk due to QTc prolongation. Besides drugs, genetic and clinical factors may contribute to QTc prolongation. The aim of this study is to examine the effect of candidate genes known for QTc prolongation and their interaction with common antipsychotics. Thus, 199 patients were genotyped for nine polymorphisms in KCNQ1, KCNH2, SCN5A, LOC10537879, LOC101927066, NOS1AP and NUBPL. QTc interval duration was measured before treatment and weekly for 5 weeks while being treated with risperidone, quetiapine, olanzapine, amisulpride, aripiprazole and haloperidol in monotherapy. Antipsychotics used in this study showed a different potential to affect the QTc interval. We found no association between KCNH2, KCNQ1, LOC10537879, LOC101927066, NOS1AP and NUBPL polymorphisms and QTc duration at baseline and during antipsychotic treatment. Mixed general models showed a significant overall influence of SCN5A (H558R) on QTc duration but no significant interaction with antipsychotic treatment. Our results do not provide evidence for an involvement of candidate genes for QTc duration in the pathophysiology of QTc prolongation by antipsychotics during short-term treatment. Further association studies are needed to confirm our findings. With a better understanding of these interactions the cardiovascular risk of patients may be decreased.

Prevalence and risk factors for prolonged QT interval and QT dispersion in patients with type 2 diabetes

AIMS

Prolonged QT interval is associated with cardiac arrhythmias and sudden death. The present study determined the prevalence of prolonged QT interval and QT dispersion and defined their clinical and metabolic predictors in patients with type 2 diabetes.

METHODS

Cross-sectional study included 501 patients with type 2 diabetes. A standard 12-lead electrocardiogram was recorded. QT corrected for heart rate (QTc) >440 ms and QT dispersion (QTd) >80 ms were considered abnormally prolonged. QTc ≥ 500 ms was considered a high-risk QTc prolongation. Demographic, clinical and laboratory data were collected. Independent risk factors for prolonged QTc and QTd were assessed using logistic regression analysis.

RESULTS

Prevalence of QTc > 440 ms and QTd > 80 ms were 44.1 and 3.6 %, respectively. Prevalence of high-risk QTc (≥500 ms) was 2 % only. Independent risk factors for QTc prolongation >440 ms were mean blood glucose (β = 2.192, p < 0.001), treatment with sulphonylurea (β = 5.198, p = 0.027), female gender (β = 8.844, p < 0.001), and coronary heart disease (β = 8.636, p = 0.001). Independent risk factors for QTc ≥ 500 ms were coronary heart disease (β = 4.134, p < 0.001) and mean blood glucose level (β = 1.735, p < 0.001). The independent risk factor for prolonged QTd was only coronary heart disease (β = 5.354, p < 0.001).

CONCLUSIONS

Although the prevalence of prolonged QTc > 440 ms is significant, the prevalence of high-risk QTc (≥500 ms) and QTd > 80 ms is very low in patients with type 2 diabetes. Hyperglycaemia and coronary heart disease are strong predictors of high-risk QTc.

Identification of Concealed and Manifest Long QT Syndrome Using a Novel T Wave Analysis Program

Background—

Congenital long QT syndrome (LQTS) is characterized by QT prolongation. However, the QT interval itself is insufficient for diagnosis, unless the corrected QT interval is repeatedly ≥500 ms without an acquired explanation. Further, the majority of LQTS patients have a corrected QT interval below this threshold, and a significant minority has normal resting corrected QT interval values. Here, we aimed to develop and validate a novel, quantitative T wave morphological analysis program to differentiate LQTS patients from healthy controls.

Methods and Results—

We analyzed a genotyped cohort of 420 patients (22±16 years, 43% male) with either LQT1 (61%) or LQT2 (39%). ECG analysis was conducted using a novel, proprietary T wave analysis program that quantitates subtle changes in T wave morphology. The top 3 discriminating features in each ECG lead were determined and the lead with the best discrimination selected. Classification was performed using a linear discriminant classifier and validated on an untouched cohort. The top 3 features were Tpeak–Tend interval, T wave left slope, and T wave center of gravity x axis (last 25% of the T wave). Lead V6 had the best discrimination. It could distinguish 86.8% of LQTS patients from healthy controls. Moreover, it distinguished 83.33% of patients with concealed LQTS from controls, despite having essentially identical resting corrected QT interval values.

Conclusions—

T wave quantitative analysis on the 12-lead surface ECG provides an effective, novel tool to distinguish patients with either LQT1/LQT2 from healthy matched controls. It can provide guidance while mutation-specific genetic testing is in motion for family members.

Update on the Diagnosis and Management of Familial Long QT Syndrome

This update was reviewed by the CSANZ Continuing Education and Recertification Committee and ratified by the CSANZ board in August 2015. Since the CSANZ 2011 guidelines, adjunctive clinical tests have proven useful in the diagnosis of LQTS and are discussed in this update. Understanding of the diagnostic and risk stratifying role of LQTS genetics is also discussed. At least 14 LQTS genes are now thought to be responsible for the disease. High-risk individuals may have multiple mutations, large gene rearrangements, C-loop mutations in KCNQ1, transmembrane mutations in KCNH2, or have certain gene modifiers present, particularly NOS1AP polymorphisms. In regards to treatment, nadolol is preferred, particularly for long QT type 2, and short acting metoprolol should not be used. Thoracoscopic left cardiac sympathectomy is valuable in those who cannot adhere to beta blocker therapy, particularly in long QT type 1. Indications for ICD therapies have been refined; and a primary indication for ICD in post-pubertal females with long QT type 2 and a very long QT interval is emerging.

A review of beat-to-beat vectorcardiographic (VCG) parameters for analyzing repolarization variability in ECG signals

Elevated ventricular repolarization lability is believed to be linked to the risk of ventricular tachycardia/ventricular fibrillation. However, ventricular repolarization is a complex electrical phenomenon, and abnormalities in ventricular repolarization are not completely understood. To evaluate repolarization lability, vectorcardiography (VCG) is an alternative approach where the electrocardiographic (ECG) signal can be considered as possessing both magnitude and direction. Recent research has shown that VCG is advantageous over ECG signal analysis for identification of repolarization abnormality. One of the key reasons is that the VCG approach does not rely on exact identification of the T-wave offset, which improves the reproducibility of the VCG technique. However, beat-to-beat variability in VCG is an emerging area for the investigation of repolarization abnormality though not yet fully realized. Therefore, the purpose of this review is to explore the techniques, findings, and efficacy of beat-to-beat VCG parameters for analyzing repolarization lability, which may have potential utility for further study.

Genetics of inherited primary arrhythmia disorders

A sudden unexplained death is felt to be due to a primary arrhythmic disorder when no structural heart disease is found on autopsy, and there is no preceding documentation of heart disease. In these cases, death is presumed to be secondary to a lethal and potentially heritable abnormality of cardiac ion channel function. These channelopathies include congenital long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, and short QT syndrome. In certain cases, genetic testing may have an important role in supporting a diagnosis of a primary arrhythmia disorder, and can also provide prognostic information, but by far the greatest strength of genetic testing lies in the screening of family members, who may be at risk. The purpose of this review is to describe the basic genetic and molecular pathophysiology of the primary inherited arrhythmia disorders, and to outline a rational approach to genetic testing, management, and family screening.

Faulty cardiac repolarization reserve in alternating hemiplegia of childhood broadens the phenotype

Alternating hemiplegia of childhood is a rare disorder caused by de novo mutations in the ATP1A3 gene, expressed in neurons and cardiomyocytes. As affected individuals may survive into adulthood, we use the term 'alternating hemiplegia'. The disorder is characterized by early-onset, recurrent, often alternating, hemiplegic episodes; seizures and non-paroxysmal neurological features also occur. Dysautonomia may occur during hemiplegia or in isolation. Premature mortality can occur in this patient group and is not fully explained. Preventable cardiorespiratory arrest from underlying cardiac dysrhythmia may be a cause. We analysed ECG recordings of 52 patients with alternating hemiplegia from nine countries: all had whole-exome, whole-genome, or direct Sanger sequencing of ATP1A3. Data on autonomic dysfunction, cardiac symptoms, medication, and family history of cardiac disease or sudden death were collected. All had 12-lead electrocardiogram recordings available for cardiac axis, cardiac interval, repolarization pattern, and J-point analysis. Where available, historical and prolonged single-lead electrocardiogram recordings during electrocardiogram-videotelemetry were analysed. Half the cohort (26/52) had resting 12-lead electrocardiogram abnormalities: 25/26 had repolarization (T wave) abnormalities. These abnormalities were significantly more common in people with alternating hemiplegia than in an age-matched disease control group of 52 people with epilepsy. The average corrected QT interval was significantly shorter in people with alternating hemiplegia than in the disease control group. J wave or J-point changes were seen in six people with alternating hemiplegia. Over half the affected cohort (28/52) had intraventricular conduction delay, or incomplete right bundle branch block, a much higher proportion than in the normal population or disease control cohort (P = 0.0164). Abnormalities in alternating hemiplegia were more common in those ≥16 years old, compared with those <16 (P = 0.0095), even with a specific mutation (p.D801N; P = 0.045). Dynamic, beat-to-beat or electrocardiogram-to-electrocardiogram, changes were noted, suggesting the prevalence of abnormalities was underestimated. Electrocardiogram changes occurred independently of seizures or plegic episodes. Electrocardiogram abnormalities are common in alternating hemiplegia, have characteristics reflecting those of inherited cardiac channelopathies and most likely amount to impaired repolarization reserve. The dynamic electrocardiogram and neurological features point to periodic systemic decompensation in ATP1A3-expressing organs. Cardiac dysfunction may account for some of the unexplained premature mortality of alternating hemiplegia. Systematic cardiac investigation is warranted in alternating hemiplegia of childhood, as cardiac arrhythmic morbidity and mortality are potentially preventable.

[Primary and secondary prophylactic ICD therapy in congenital electrical and structural cardiomyopathies]

Congenital electrical and structural cardiomyopathies are rare and associated with an increased risk for syncope and sudden cardiac death in the young. Due to the young age of the patients and the limited data available, risk stratification and especially ICD therapy are challenging. In this young patient collective, ICD therapy is associated with a high complication rate, which does not justify unreserved primary prophylactic ICD implantation. The aim of this review is to elucidate risk stratification and ICD therapy of various electrical and structural cardiomyopathies.

Must every child with long QT syndrome take a beta blocker?

Long QT syndrome is the most commonly recognised cause of sudden cardiac death in children. With a prevalence of 1 in 2000, family screening is identifying large numbers of hitherto asymptomatic gene carriers in the community, about a third of whom have a normal QT interval. The mainstay of treatment is long term uninterrupted beta blocker therapy, a treatment with many potential side effects. This article reviews the evidence and suggests a cohort who may, after assessment in a specialised cardiac-genetic clinic, be spared this treatment because of very low baseline risk. These are asymptomatic boys and prepubertal girls with a heart rate corrected QT interval persistently less than 470 ms who do not indulge in high risk activities (especially swimming) and do not have a missense mutation in the c-loop region of the KCNQ1 (long QT 1) gene.

Sports Participation in Genotype Positive Children With Long QT Syndrome

OBJECTIVE

The study sought to examine the prevalence and outcomes of sports participation (both competitive and recreational) in our single-center LQTS genotype positive pediatric population.

BACKGROUND

The risks of sports participation in patients with long QT syndrome (LQTS) are not clearly elucidated.

METHODS

A retrospective review was performed on genotype positive patients referred for the evaluation and management of LQTS between 1998 and 2013 at the Children's Hospital of Philadelphia. Pediatric patients participating in competitive or recreational sports were included in the analysis and their charts were reviewed for documented LQTS events during follow-up.

RESULTS

The cohort of genotype-positive LQTS patients included 212 patients, and 103 patients (49%, female n = 53, average follow-up 7.1 ± 4.0 years, average QTc 468 ± 42 ms) participated in sports. A total of 105 LQTS disease-causing mutations were identified: KCNQ1 n = 60 (58%), KCNH2 n = 36 (35%), SCN5A n = 6 (6%), KCNE1 n = 1 (1%), and KCNE2 n = 2 (2%). All patients were treated with beta-blockade, with noncompliance in 1 patient and intolerance in 1 patient. Twenty-six patients participated in competitive sports (26%, female n = 15, average follow-up 6.9 ± 4.1 years, average QTc 461 ± 35 ms). Seventy-seven patients (75%, female n = 35, average follow-up 7.3 ± 3.9 years, average QTc 470 ± 43 ms) participated in recreational sports. No patients had LQTS symptoms during sports participation. Five appropriate implantable cardioverter-defibrillator shocks occurred in 2 patients, though none were related to sports participation.

CONCLUSIONS

In this series no cardiac events and no deaths were observed in treatment-compliant LQTS children while participating in sports in 755 patient-years of follow-up.

Prognostic implications of mutation-specific QTc standard deviation in congenital long QT syndrome

BACKGROUND

Individual corrected QT interval (QTc) may vary widely among carriers of the same long QT syndrome (LQTS) mutation. Currently, neither the mechanism nor the implications of this variable penetrance are well understood.

OBJECTIVES

To hypothesize that the assessment of QTc variance in patients with congenital LQTS who carry the same mutation provides incremental prognostic information on the patient-specific QTc.

METHODS

The study population comprised 1206 patients with LQTS with 95 different mutations and ≥ 5 individuals who carry the same mutation. Multivariate Cox proportional hazards regression analysis was used to assess the effect of mutation-specific standard deviation of QTc (QTcSD) on the risk of cardiac events (comprising syncope, aborted cardiac arrest, and sudden cardiac death) from birth through age 40 years in the total population and by genotype.

RESULTS

Assessment of mutation-specific QTcSD showed large differences among carriers of the same mutations (median QTcSD 45 ms). Multivariate analysis showed that each 20 ms increment in QTcSD was associated with a significant 33% (P = .002) increase in the risk of cardiac events after adjustment for the patient-specific QTc duration and the family effect on QTc. The risk associated with QTcSD was pronounced among patients with long QT syndrome type 1 (hazard ratio 1.55 per 20 ms increment; P<.001), whereas among patients with long QT syndrome type 2, the risk associated with QTcSD was not statistically significant (hazard ratio 0.99; P = .95; P value for QTcSD-by-genotype interaction = .002).

CONCLUSIONS

Our findings suggest that mutations with a wider variation in QTc duration are associated with increased risk of cardiac events. These findings appear to be genotype-specific, with a pronounced effect among patients with the long QT syndrome type 1 genotype.

In silico cardiac risk assessment in patients with long QT syndrome: type 1: clinical predictability of cardiac models

OBJECTIVES

The study was designed to assess the ability of computer-simulated electrocardiography parameters to predict clinical outcomes and to risk-stratify patients with long QT syndrome type 1 (LQT1).

BACKGROUND

Although attempts have been made to correlate mutation-specific ion channel dysfunction with patient phenotype in long QT syndrome, these have been largely unsuccessful. Systems-level computational models can be used to predict consequences of complex changes in channel function to the overall heart rhythm.

METHODS

A total of 633 LQT1-genotyped subjects with 34 mutations from multinational long QT syndrome registries were studied. Cellular electrophysiology function was determined for the mutations and introduced in a 1-dimensional transmural electrocardiography computer model. The mutation effect on transmural repolarization was determined for each mutation and related to the risk for cardiac events (syncope, aborted cardiac arrest, and sudden cardiac death) among patients.

RESULTS

Multivariate analysis showed that mutation-specific transmural repolarization prolongation (TRP) was associated with an increased risk for cardiac events (35% per 10-ms increment [p < 0.0001]; ≥upper quartile hazard ratio: 2.80 [p < 0.0001]) and life-threatening events (aborted cardiac arrest/sudden cardiac death: 27% per 10-ms increment [p = 0.03]; ≥upper quartile hazard ratio: 2.24 [p = 0.002]) independently of patients' individual QT interval corrected for heart rate (QTc). Subgroup analysis showed that among patients with mild to moderate QTc duration (<500 ms), the risk associated with TRP was maintained (36% per 10 ms [p < 0.0001]), whereas the patient's individual QTc was not associated with a significant risk increase after adjustment for TRP.

CONCLUSIONS

These findings suggest that simulated repolarization can be used to predict clinical outcomes and to improve risk stratification in patients with LQT1, with a more pronounced effect among patients with a lower-range QTc, in whom a patient's individual QTc may provide less incremental prognostic information.

A novel mutation in the transmembrane nonpore region of the KCNH2 gene causes severe clinical manifestations of long QT syndrome

BACKGROUND

Long QT syndrome (LQTS) is characterized by prolonged ventricular repolarization and variable clinical course with arrhythmia-related syncope and sudden death. Mutations in the nonpore region of the LQTS-associated KCNH2 gene (also known as hERG) are mostly associated with coassembly or trafficking abnormalities, resulting in haplotype insufficiency and milder clinical phenotypes compared with mutations in the pore domain.

OBJECTIVE

To investigate the effect of a nonpore mutation on the channel current, which was identified from an LQTS family with severe clinical phenotypes.

METHODS

Two members of a Japanese family with LQTS were searched for mutations in KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, and KCNJ2 genes by using automated DNA sequencing. We characterized the electrophysiological properties and glycosylation pattern of the mutant channels by using patch clamp recording and Western blot analysis.

RESULTS

In the LQTS patient with torsades de pointes and cardiopulmonary arrest, we identified the novel T473P mutation in the transmembrane nonpore region of KCNH2. The proband's father carried the same mutation and showed prolonged corrected QT interval and frequent torsades de pointes in the presence of hypokalemia following the administration of garenoxacin. Patch clamp analysis in heterologous cells showed that hERG T473P channels generated no current and exhibited a dominant negative effect when coexpressed with wild-type protein. Only incompletely glycosylated hERG T473P channels were observed by using Western blot analysis, suggesting impaired trafficking.

CONCLUSIONS

These results demonstrated that a trafficking-deficient mutation in the transmembrane nonpore region of KCNH2 causes a dominant negative effect and a severe clinical course in affected patients.

Repolarization syndromes

Repolarization syndromes, including early repolarization, Brugada, and short and long QT, have been implicated increasingly as causes of sudden cardiac death (SCD) despite no obvious mechanical cardiac abnormalities. So-called idiopathic ventricular fibrillation is now often reassigned to one of the aforementioned entities. Underlying causes are diverse; genetic mutation has been proven in many but not all cases. Although high-risk individuals generally can be identified, most of the potential victim pool is still unknown and cannot be discovered at this time. Awareness of these entities' existence, knowledge of family history, and 12-lead electrocardiography are the initial steps toward preventing SCD in this population. Underlying mechanisms for ventricular tachycardia/fibrillation in such individuals include phase 2 reentry, early after depolarization, and vortex reentry. For the time-being, although most forms of long QT syndrome can be treated with β-blockers, an implantable cardioverter-defibrillator remains the only definitive therapy for the prevention of arrhythmic death among high-risk populations.

Congenital long and short QT syndromes

Congenital long and short QT syndromes are familial arrhythmias characterized by derangement of repolarization and a high risk of sudden cardiac death due to ventricular tachyarrhythmias. With growing understanding of these syndromes in both the medical and lay communities, diagnostic and therapeutic difficulties are increasingly faced by health care providers. Modern genomics has determined the mechanism of arrhythmia induction in these patients, resulting in specific medical therapies and improved risk stratification. This paper reviews the common presentations, genetic etiology, basic evaluation, risk stratification, and therapeutic approach for both syndromes. Particular attention is paid to the effect of the individual syndrome on the cardiac action potential and its correlate the surface 12 lead ECG. In conclusion, patients with long and short QT syndromes are at risk for sudden death, with accurate diagnosis, risk stratification, and resulting appropriate therapy favorably altering their outcome.

Association between Tp-e/QT ratio and prognosis in patients undergoing primary percutaneous coronary intervention for ST-segment elevation myocardial infarction

BACKGROUND

Both the Tpeak-Tend interval (Tp-e) and the Tp-e/QT ratio have been linked to increased risk for arrhythmia. Patient Tp-e/QT ratios were investigated prior to primary percutaneous coronary intervention (pPCI) in patients with ST-segment elevation myocardial infarction (STEMI).

HYPOTHESIS

Tp-e/QT ratio maybe associated with the prognosis in patients with ST-segment elevation.

METHODS

A total of 338 patients (N = 338) with STEMI treated by pPCI were included. The Tp-e and Tp-e/QT ratio were determined using electrocardiograms in the subjects exhibiting ST-segment elevation.

RESULTS

The Tp-e/QT ratio was correlated with both short- and long-term outcomes. Analysis of the receiver operating characteristic curve demonstrated that the optimal cutoff value for outcome prediction was a Tp-e/QT ratio of 0.29. Of the 388 patients enrolled, 115 (34.0%) exhibited a Tp-e/QT ratio ≥ 0.29. Patients with a Tp-e/QT ratio ≥ 0.29 showed elevated rates of both in-hospital death (21.9% vs 2.3%; P < 0.001) and main adverse cardiac events (MACE) (48.1% vs 15.3%; P < 0.005). After discharge, Tp-e/QT ratios ≥ 0.29 remained an independent predictor of all-cause death (35.5% vs 5.2%, P < 0.001) and cardiac death (32.3% vs 2.6%, P < 0.001).

CONCLUSIONS

The Tp-e/QT ratio may serve as a prognostic predictor of adverse outcomes after successful pPCI treatment in STEMI patients.

Derivation and Validation of a Simple Exercise-Based Algorithm for Prediction of Genetic Testing in Relatives of LQTS Probands

Background—

Genetic testing can diagnose long-QT syndrome (LQTS) in asymptomatic relatives of patients with an identified mutation; however, it is costly and subject to availability. The accuracy of a simple algorithm that incorporates resting and exercise ECG parameters for screening LQTS in asymptomatic relatives was evaluated, with genetic testing as the gold standard.

Methods and Results—

Asymptomatic first-degree relatives of genetically characterized probands were recruited from 5 centers. QT intervals were measured at rest, during exercise, and during recovery. Receiver operating characteristics were used to establish optimal cutoffs. An algorithm for identifying LQTS carriers was developed in a derivation cohort and validated in an independent cohort. The derivation cohort consisted of 69 relatives (28 with LQT1, 20 with LQT2, and 21 noncarriers). Mean age was 35±18 years, and resting corrected QT interval (QTc) was 466±39 ms. Abnormal resting QTc (females ≥480 ms; males ≥470 ms) was 100% specific for gene carrier status, but was observed in only 48% of patients; however, mutations were observed in 68% and 42% of patients with a borderline or normal resting QTc, respectively. Among these patients, 4-minute recovery QTc ≥445 ms correctly restratified 22 of 25 patients as having LQTS and 19 of 21 patients as being noncarriers. The combination of resting and 4-minute recovery QTc in a screening algorithm yielded a sensitivity of 0.94 and specificity of 0.90 for detecting LQTS carriers. When applied to the validation cohort (n=152; 58 with LQT1, 61 with LQT2, and 33 noncarriers; QTc=443±47 ms), sensitivity was 0.92 and specificity was 0.82.

Conclusions—

A simple algorithm that incorporates resting and exercise-recovery QTc is useful in identifying LQTS in asymptomatic relatives.

Impaired cardiac sympathetic innervation in symptomatic patients with long QT syndrome

PURPOSE

Increased sympathetic activation is a key modifier for arrhythmogenesis in patients with long QT syndrome (LQTS), a congenital channelopathy. Therefore, we investigated cardiac sympathetic function using 123I-metaiodobenzylguanidine (MIBG) single photon emission computed tomography (SPECT) in a cohort of symptomatic LQTS patients and correlated these findings with the underlying genotype.

METHODS

[123I]MIBG SPECT was performed in 28 LQTS patients. Among these, 18 patients (64%) had a previous syncope and 10 patients (36%) survived sudden cardiac arrest. Patients were characterized in terms of genetic subtypes and QTc interval on surface ECGs. SPECT images were analysed for regional [123I]MIBG uptake in a 33-segment bullseye scheme and compared to those obtained from 10 age-matched healthy control subjects (43±12 years).

RESULTS

An abnormal 123I-MIBG scan was found in 17 of 28 LQTS patients (61%) with a tracer reduction mainly located in the anteroseptal segments of the left ventricle. This finding was independent of the genetic LQTS subtype. In addition, no differences were found between LQTS patients with a QTc>500 ms vs <500 ms or those suffering from syncope vs VF (p>0.05).

CONCLUSION

A distinct regional pattern of impaired cardiac sympathetic function was identified in the majority of symptomatic LQTS patients. This innervation defect was independent of the underlying genotype and clinical disease expression.