Author + information
- Received August 4, 2015
- Revision received December 11, 2015
- Accepted January 7, 2016
- Published online June 1, 2016.
- Kenshi Hayashi, MD, PhDa,
- Tetsuo Konno, MD, PhDa,
- Noboru Fujino, MD, PhDa,
- Hideki Itoh, MD, PhDb,
- Yusuke Fujii, MDb,
- Yoko Imi-Hashida, MD, PhDc,
- Hayato Tada, MD, PhDa,
- Toyonobu Tsuda, MDa,
- Yoshihiro Tanaka, MDa,
- Takekatsu Saito, MD, PhDc,
- Hidekazu Ino, MD, PhDd,
- Masa-aki Kawashiri, MD, PhDa,
- Kunio Ohta, MD, PhDc,
- Minoru Horie, MD, PhDb and
- Masakazu Yamagishi, MD, PhDa,∗ ()
- aDivision of Cardiovascular Medicine, Kanazawa University Graduate School of Medicine, Kanazawa, Japan
- bDepartment of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
- cDepartment of Pediatrics, Kanazawa University, Kanazawa, Japan
- dDepartment of Cardiovascular Medicine, Komatsu Municipal Hospital, Komatsu, Japan
- ↵∗Reprint requests and correspondence:
Dr. Masakazu Yamagishi, Division of Cardiovascular Medicine, Kanazawa University Graduate School of Medicine, 13-1, Takara-machi, Kanazawa, Ishikawa 920-8640, Japan.
Objectives In this study, we scored patients with long QT syndrome (LQTS) according to the different Schwartz diagnostic criteria from 1993, 2006, and 2011, and to examine the validation of the criteria in relevance to the frequency of LQTS-related gene mutation.
Background Although updated diagnostic criteria have been used in clinical settings, few data exist regarding their impact on the diagnosis of LQTS.
Methods We used a cohort of 132 patients who presented with prolonged QTc intervals and/or abnormal clinical history in cardiac screening and who underwent exercise stress testing. LQTS scores of ≥3.5 points according to the 2006 and the 2011 criteria were considered to indicate a high probability of LQTS, as opposed to the 4 points used by the 1993 criteria. The 2011 criteria were updated by adding the evaluation of the recovery phase of exercise.
Results The 2011 criteria significantly increased the number of high probability patients (n = 62) compared with the 1993 criteria (n = 32; p = 0.0002) or the 2006 criteria (n = 36; p = 0.0014). The percentage of mutation carriers in those with an intermediate score, which was rather high using the 1993 (53%) and 2006 criteria (53%), was greatly reduced with the 2011 criteria (15%, p = 0.0014 vs. the 1993 criteria, and p = 0.0013 vs. the 2006 criteria). Among 54 mutation carriers, the 1993, the 2006, and the 2011 criteria identified a high probability of carriers in 25 patients (46% sensitivity and 91% specificity), 27 patients (50% sensitivity and 88% specificity), and 48 patients (89% sensitivity and 82% specificity), respectively.
Conclusions The use of the 2011 criteria will facilitate the diagnosis of LQTS and will decrease the number of false negative results.
The long QT syndrome (LQTS) is an inherited disorder characterized by delayed cardiac repolarization with abnormal T-wave morphology and a possibility of lethal ventricular tachyarrhythmias, which result in fainting spells and sudden death (1). Mutations in various cardiac ion channel genes, including KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, KCNJ2, and CACNA2, or a membrane adaptor protein gene, ANKB, are known to cause this syndrome (2), and many LQTS mutations have been identified (3,4). Sixteen genetic forms of LQTS have been described; however, the most prevalent forms are LQT1 and LQT2, which are associated with mutations in potassium channels, and LQT3, which is associated with a sodium channel mutation (2,5).
Originally, the diagnostic criteria for LQTS were proposed by Schwartz et al. in 1985 (6). Diagnoses were based on major and minor criteria, and the diagnosis could be made in the presence of either 2 major criteria or of 1 major and 2 minor criteria. These first criteria are clinically useful; however, they are nonquantitative. Subsequently, Schwartz et al. published diagnostic criteria that included points assigned to a patient’s symptoms, medical and family history, and electrocardiography (ECG) findings (7). A Schwartz score of ≥4 in a patient indicated a high probability of a LQTS diagnosis. Molecular diagnosis of LQTS showed that disease penetrance was low (25%) in some families with congenital LQTS (8), and QT duration appeared normal in 10% (LQT3) to 36% (LQT1) of genotype-positive patients (9). A previous study showed that, based on the Schwartz criteria, 43% of patients with Schwartz scores of <4 were genotype-positive (10). Thus, the 1993 criteria were not helpful in identifying asymptomatic mutation carriers with a normal QT interval on a ECG at rest. In contrast, this subclinical type of LQTS is one of the risk factors for drug-induced Torsade de pointes (11). The 1993 criteria were modified by Schwartz et al. in 2006 (12). The fundamental difference was in considering a score of ≥3.5 points, rather than 4 points, as an indication of a high probability of LQTS.
Exercise testing (13–15) or an epinephrine QT stress test (16,17) can unmask patients with occult LQTS, particularly LQT1. Several studies showed that the increase in QTc during the recovery phase of exercise testing could distinguish patients with LQTS from control subjects (13–15). Although the evaluation parameters of the recovery phase of exercise were added to the LQTS diagnostic criteria in 2011 (18), little data exist regarding the clinical impact of the 2011 criteria. More recently, the Heart Rhythm Society (HRS)/European Heart Rhythm Association (EHRA)/Asia Pacific Heart Rhythm Society (APHRS) Expert Consensus Statement showed that LQTS could also be diagnosed in the presence of an unequivocally pathogenic mutation in one of the LQTS genes (19). Thus, the detection of LQTS gene mutation carriers is of clinical importance for the diagnosis of LQTS. Therefore, in our cohort of LQTS patients, we compared the LQTS scores calculated by the conventional Schwartz criteria with those calculated using the 2011 criteria (which included an evaluation of the recovery phase of exercise testing). We also performed genetic testing of the major LQTS genes, and we compared the frequency of mutation carriers in the high probability LQTS groups who were diagnosed using the 1993, 2006, and 2011 criteria.
The study population consisted of 132 patients who presented with prolonged QTc intervals, and/or abnormal clinical history and familial findings during cardiac screening; all patients were referred to our hospital. These patients underwent the following examinations: ECG recording at rest, exercise stress test, LQTS score calculations, and genetic testing. A cumulative LQTS risk score was calculated using the 1993 (7), 2006 (12), and 2011 LQTS diagnostic criteria (18).
The study observed the principles outlined in the Declaration of Helsinki and was approved by the Ethics Committee for Medical Research at our institution. All study patients provided written informed consent before registration.
All referred patients had standard 12-lead ECGs at rest and exercise stress tests recorded at the hospital. The QT interval was measured manually, and was defined as the time between the onset of QRS and the point at which the isoelectric line intersected a tangential line drawn at the maximal downslope of the positive T-wave. QT interval measurements were the means of 3 consecutive beats on 1 lead (lead V5), because taking only the longest observed QTc would result in a higher rate of false positive classifications (20).
Clinical diagnosis of LQTS by Schwartz score
The conventional 1993 criteria score a patient’s probability of LQTS based on ECG findings, clinical history, and family history (7). Patients who have never experienced the common LQTS symptoms, including recurrent syncope, seizures, and aborted cardiac death, were considered asymptomatic. The patients were divided into 3 LQTS probability categories based on the risk score: ≥4 points, high probability; 2 to 3 points, intermediate probability; and ≤1 point, low probability. The updated criteria modified by Schwartz in 2006 and 2011 categorized patients as follows: ≥3.5 points, high probability; 1.5 to 3 points, intermediate probability; and ≤1 point, low probability (12,18). The last updated 2011 criteria included an evaluation of the recovery phase of exercise testing.
DNA isolation and mutation analysis
Genomic DNA was amplified using a standard polymerase chain reaction method. High-resolution melting (HRM) curve analysis (LightScanner, BioFire Defense, Salt Lake City, Utah) or denaturing high-performance liquid chromatography (dHPLC) (WAVE System Model 3500, Transgenomic, Omaha, Nebraska) were used to screen for KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, and KCNJ5. Samples in which the melting curve deviated from the wild-type control were subjected to DNA direct sequencing.
Interpretation of sequence variants
Variants of minor allele frequency (MAF) of <1% in the East Asian population from the Exome Aggregation Consortium (ExAC) were defined as rare. Combined Annotation Dependent Depletion (CADD) software was applied to predict the pathogenicity of LQTS-associated variants. CADD scores objectively integrate many diverse annotations into a single measure (C-score), and a scaled C-score of ≥10 indicates that the variant is predicted to be among the 10% most deleterious substitutions that can occur in the human genome: 1) rare and null (nonsense, frameshift, canonical with or without 1 or 2 splice sites) variants; and/or 2) rare variants with a C-score of ≥10 were considered pathogenic.
The chi-square test and Fisher's exact test were used to assess the hypothesis of independence between categorical variables. The Student’s t-test was applied for comparison of means between 2 groups. Bonferroni’s correction was performed for multiple comparisons. Receiver-operator characteristic (ROC) curve analysis and the area under the ROC curve (AUC) were used to quantify the ability of Schwartz scores to detect LQTS mutation carriers. A p value of <0.05 was considered statistically significant. Statistical analysis was performed using JMP Pro 11.0.0 (SAS Institute Inc., Cary, North Carolina) and Origin 9.0 (OriginLab, Northampton, Massachusetts).
Baseline characteristics and ECG parameters
Table 1 summarizes the patient characteristics for the entire cohort (n = 132) and for patients categorized according to the recovery phase QTc during exercise stress testing (QTc ≥480 ms, n = 72 vs. QTc <480 ms; n = 60). A total of 29 of 132 patients (72 women; mean age 18 ± 14 years) had a family history of LQTS, and 26 had a history of syncope or aborted cardiac arrest. More patients with a QTc ≥480 ms at the 4-min recovery phase had a positive family history or a cardiac event than those with a QTc <480 ms (Table 1).
Genetic analyses revealed 21 patients with 12 single KCNQ1 mutations, 21 patients with 16 single KCNH2 mutations, 4 patients with 4 single SCN5A mutations, 1 patient with a single KCNE1 mutation, and 5 patients with 4 compound mutations (Tables 1 and 2). The MAFs for all mutations were <1% in the East Asian population in the ExAC data and browser, and the CADD scores for all variants were >10 (Table 2). Forty-four of 72 patients with prolonged QTc at the recovery phase had LQTS-related mutations, whereas 8 of 60 patients without prolonged QTc at the recovery phase had LQTS-related mutations (p < 0.0001). Twenty of 72 patients with a QTc ≥480 ms after exercise had LQT1 mutations, whereas there was only 1 patient of 60 patients who did not have post-exercise QTc prolongation (p < 0.0001) (Table 1).
Distribution of study patients according to each criteria
Based on the 1993 and the 2006 LQTS criteria, 32 and 36 of 132 patients were diagnosed as having a high probability of LQTS, respectively (Table 1, Figure 1). Interestingly, the application of the 2011 criteria significantly increased the number of patients with a high probability of LQTS (32 vs. 62, 1993 vs. 2011; p = 0.0002, and 36 vs. 62, 2006 vs. 2011; p = 0.0014) (Figure 1). Of the 72 patients with post-exercise QTc ≥480 ms, 29 and 31 patients were diagnosed with a high probability of LQTS by the 1993 and the 2006 criteria, respectively. In contrast, 57 of these 72 patients were diagnosed with a high probability of LQTS by the 2011 criteria (p < 0.0001 vs. the 1993 or 2006 criteria) (Table 1).
Frequency of LQTS mutation carriers and diagnostic performance for mutation carriers—differences among the 3 diagnostic criteria
The probability of carrying mutations in patients with a high probability for LQTS was comparable among the 1993, 2006, and 2011 criteria; there were 23 of 32 patients (72%), 25 of 36 patients (69%), and 46 of 62 patients (74%), respectively (Figure 1). However, in the intermediate probability groups, the frequency of mutation carriers according to the 1991 and the 2006 criteria was 27 of 51 patients (53%) and 25 of 47 patients (53%), which was significantly higher than the 4 of 27 patients (15%) according to the 2011 criteria (p < 0.0014 vs. the 1993 criteria, and p < 0.0013 vs. the 2006 criteria) (Figure 1). Figure 2 shows that most mutation carriers who were diagnosed with intermediate probability using the conventional criteria were diagnosed as high probability by the 2011 criteria, regardless of LQTS genotype. The application of the 2011 criteria significantly increased the number of mutation carriers with a high probability of LQTS (23 vs. 46, 1993 vs. 2011; p < 0.0001, and 25 vs. 46, 2006 vs. 2011; p < 0.0001) (Figure 2).
Table 3 and Figure 3 show that a high probability of LQTS diagnosed using the 1993 and the 2006 criteria could predict mutation carriers with 44% sensitivity (23 of 52 patients) and 89% specificity (71 of 80 patients) and with 48% sensitivity (25 of 52 patients) and 86% specificity (69 of 80 patients), respectively. In contrast, a high probability diagnosed using the 2011 criteria predicted mutation carriers with 88% sensitivity (46 of 52 patients) and 80% specificity (64 of 80 patients). The sensitivity for detecting mutation carriers was significantly different between the 1993 and the 2011 criteria, and the 2006 and the 2011 criteria (p < 0.0001, respectively). The negative predictive value for detecting mutation carriers with the 2011 criteria was 91%, which was significantly higher than that of the 1993 criteria (71%) or the 2006 criteria (72%) (p = 0.001 and p = 0.0026, respectively).
Among 52 mutation carriers, QTc ≥480 ms after exercise testing was observed in 44 patients, yielding a sensitivity of 85%. Similarly, 52 of 80 patients who were mutation-negative showed a QTc of <480 ms after exercise testing, yielding a 65% specificity (Table 3, Figure 3). The sensitivity for detecting mutation carriers using post-exercise QTc was significantly higher than that of the 1993 criteria or the 2006 criteria; however, the specificity using the post-exercise QTc was significantly lower compared with that of these criteria (Figure 3).
Frequency of symptomatic LQTS patients by conventional and updated criteria
In our cohort, 26 patients were symptomatic (syncope in 25 patients and aborted cardiac arrest in 1 patient) before the introduction of beta-blocker therapy (Table 1, Figure 4). The frequency of symptomatic patients in those with a high probability using the 1993 criteria was 59% (19 of 32 patients), which was higher compared with the 34% (21 of 62 patients) using the 2011 criteria (p = 0.0272). However, the difference was not significant after the Bonferroni correction (Figure 4).
Diagnostic performance of the updated criteria
To confirm the diagnostic accuracy of the 2011 updated criteria, ROC curves were constructed for predicting LQTS mutation carriers and detecting symptomatic LQTS patients using the updated criteria. The AUC for LQTS mutation carriers was 0.88 (95% confidence interval: 0.81 to 0.94) (Figure 5). The optimal cutoff value for predicting LQTS mutation carriers was 3.5.
The present study demonstrated that: 1) more patients were diagnosed with a high probability of LQTS by the 2011 criteria compared with the 1993 or the 2006 criteria (Figure 1); 2) in the groups with intermediate probability of LQTS, more mutation carriers were diagnosed in the 1993 or the 2006 than in the 2011 criteria group (Figure 1); and 3) both the sensitivity and the negative predictive value for detecting mutation carriers using the 2011 criteria were significantly higher than those of the 1993 or the 2011 criteria (Figures 1 and 3, Table 3).
Schwartz et al. (6) proposed a first set of diagnostic criteria for LQTS in 1985, which provided a logical and quantitative approach to the clinical diagnosis of LQTS. They reported LQTS diagnostic criteria in 1993 based on clinical presentation, including ECG, and clinical and familial findings (7), and arbitrarily modified the criteria in 2006 (12). Recently, the diagnostic criteria were updated by adding a more objective parameter, the evaluation of the recovery phase of exercise (18). Vincent et al. (13) reported that the QTc of normal subjects showed no significant changes during exercise compared with the value at rest, whereas those with Romano-Ward syndrome demonstrated a significant increase in QTc both before and after exercise. In this study, 29 of 32 patients, 31 of 36 patients, and 57 of 62 with a high probability of LQTS diagnosed by the 1993, the 2006, or the 2011 criteria, respectively, showed prolonged QTc ≥480 ms after exercise (Table 1).
Asymptomatic mutation carriers who show a normal QT interval might be overlooked by applying the 1993 LQTS diagnostic criteria, because these criteria do not consider any molecular diagnostic characteristics of LQTS. A previous study showed a correlation between the conventional Schwartz score and the results of genetic testing (10). In 123 patients with a high probability of LQTS (score ≥4), 89 patients were genotype-positive (72%), whereas among 215 patients with a score <4, 93 patients were still genotype-positive (43%) (10). In addition, in this study, the percentages of positive genotypes in patients with high and intermediate probability by the 1993 criteria were 72% and 53%, respectively. These percentages were comparable with those calculated using the 2006 criteria (69% and 53%). In contrast, the application of the 2011 criteria resulted in the maintenance of the percentage of genotype-positive patients with a high probability of LQTS (74%), while significantly reducing that in patients with intermediate probability (15%; p = 0.0002 vs. the 1993 criteria, and p = 0.0014 vs. the 2006 criteria), regardless of the LQTS genotype (Figure 2).
The 1993 LQTS diagnostic criteria also had low sensitivity in identifying disease carriers. A previous study showed that 89 of 218 genotype-positive LQTS patients were diagnosed with a high probability of LQTS, yielding a 41% sensitivity (10). This value was similar to our results: 44% by the 1993 criteria and 48% by the 2006 criteria. In contrast, the sensitivity significantly increased to 88% using the 2011 criteria. In this way, the 2011 criteria could detect more asymptomatic LQTS mutation carriers in addition to symptomatic LQTS patients in advance of gene analysis.
Several studies reported that further QTc prolongation after exercise could be useful for identifying LQTS mutation carriers (14,15). Horner et al. (15) performed treadmill stress tests in 243 LQTS patients and showed that stress testing could unmask patients with occult LQTS, particularly LQT1. They also reported that LQT2 and LQT3 patients responded similarly to each other in peak exercise with an initial shortening of their QTc, which was then followed by a gradual increase in their QTc in recovery, which approached their respective QTc intervals at rest (15). In this study, the prolonged QTc ≥480 ms after exercise predicted mutation carriers with 85% sensitivity and 65% specificity. The sensitivity of this test is reasonable; however, the specificity was lower compared with that of the 1993 or the 2006 diagnostic criteria.
The number of symptomatic LQTS patients in the group with a high probability of LQTS were similar, irrespective of the diagnostic criteria used (19 using the 1993 criteria and 20 using the 2006 criteria vs. 21 using the 2011 criteria) (Figure 4). However, the proportion of symptomatic patients with a higher probability of LQTS diagnosed using the 1993 criteria (59%) was higher compared with that of patients diagnosed using the 2011 criteria (34%). Based on these findings, the 1993 criteria could be useful for detecting more symptomatic LQTS patients.
First, it was a retrospective study with a modest sample size. However, this study demonstrated the significance of the 2011 criteria in terms of an increase in the diagnosis of patients with a high probability of LQTS-related gene mutations. Statistical significance with small sample sizes might be spurious, and conclusions might be limited. In addition, some statistical comparisons were made between subsamples, which might further limit confidence in the results, especially whether they were statistically significant. Second, genetic screening were performed by HRM or dHPLC followed by Sanger sequencing. However, these techniques have been used successfully for screening. Compared with DNA sequencing, the overall sensitivity and specificity of HRM were 0.99 and 0.96, and those of dHLPC were 0.88 and 0.97, respectively (21). Finally, the genotyped mutation carriers in this study were mainly LQT1 and LQT2 genotyped patients. However, because the most prevalent forms of LQTS are LQT1 and LQT2 in general, our study population did not limit the generalizability of results.
These results demonstrate that the 2011 LQTS diagnostic criteria can identify more silent LQTS-related gene mutation carriers as being at a high probability of LQTS, which cannot be identified by the conventional criteria. We suggest that the use of the 2011 criteria will facilitate the diagnosis of LQTS and will avoid a number of false negative results.
COMPETENCY IN MEDICAL KNOWLEDGE: LQTS is diagnosed in the presence of an LQTS risk score of ≥3.5 and/or an unequivocally pathogenic mutation in 1 of the LQTS genes, or a QTc of ≥500 ms in repeated 12-lead ECG. Asymptomatic mutation carriers with a normal QT interval might be overlooked by applying the conventional LQTS diagnostic criteria.
TRANSLATIONAL OUTLOOK: The 2011 LQTS diagnostic criteria can identify more silent LQTS-related gene mutation carriers as having a high probability of LQTS, which cannot be identified by the conventional criteria. Further larger studies with a comprehensive mutation analysis are required to establish the utility of the 2011 criteria for clinical detection of LQTS patients with gene mutations.
The authors gratefully acknowledge Akihiro Nomura for helpful discussions, and Takako Obayashi, Masako Fukagawa, Hitomi Oikawa, Kazu Toyo-oka, Madoka Tanimoto, and Arisa Ikeda for technical assistance.
Drs. Hayashi and Horie received grants from the Ministry of Health, Labor and Welfare of Japan for Clinical Research on Intractable Diseases (H26-040, H24-033). Drs. Hayashi and Yamagishi has received TR funds from the Japanese Circulation Society.
All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Abbreviations and Acronyms
- area under the receiver-operating characteristic curve
- combined annotation dependent depletion
- denaturing high-performance liquid chromatography
- high-resolution melting
- long QT syndrome
- minor allele frequency
- negative predictive value
- positive predictive value
- receiver-operating characteristic
- Received August 4, 2015.
- Revision received December 11, 2015.
- Accepted January 7, 2016.
- American College of Cardiology Foundation
- Moss A.J.,
- Schwartz P.J.,
- Crampton R.S.,
- et al.
- Hayashi K.,
- Shimizu M.,
- Ino H.,
- et al.
- Schwartz P.J.,
- Ackerman M.J.,
- George A.L. Jr..,
- Wilde A.A.
- Schwartz P.J.,
- Moss A.J.,
- Vincent G.M.,
- Crampton R.S.
- Priori S.G.,
- Napolitano C.,
- Schwartz P.J.
- Tester D.J.,
- Will M.L.,
- Haglund C.M.,
- Ackerman M.J.
- Takenaka K.,
- Ai T.,
- Shimizu W.,
- et al.
- Shimizu W.,
- Noda T.,
- Takaki H.,
- et al.
- Schwartz P.J.,
- Crotti L.
- Priori S.G.,
- Wilde A.A.,
- Horie M.,
- et al.
- ↵Tester DJ SP, Ackerman MJ. Congenital long QT syndrome. In: Gussak I, Antzelevitch C, eds. Electorical diseases of the heart. 2nd Ed. Berlin, Germany: Springer, 2013:439–68.