Incidence and Risk Factors of Arrhythmic Events in Catecholaminergic Polymorphic Ventricular Tachycardia
Background— The pathophysiological background of catecholaminergic polymorphic ventricular tachycardia is well understood, but the clinical features of this stress-induced arrhythmic disorder, especially the incidence and risk factors of arrhythmic events, have not been fully ascertained.
Methods and Results— The outcome in 101 catecholaminergic polymorphic ventricular tachycardia patients, including 50 probands, was analyzed. During a mean follow-up of 7.9 years, cardiac events defined as syncope, aborted cardiac arrest, including appropriate discharges from implantable defibrillators, or sudden cardiac death occurred in 27 patients, including 2 mutation carriers with normal exercise tests. The estimated 8-year event rate was 32% in the total population and 27% and 58% in the patients with and without β-blockers, respectively. Absence of β-blockers (hazard ratio [HR], 5.48; 95% CI, 1.80 to 16.68) and younger age at diagnosis (HR, 0.54 per decade; 95% CI, 0.33 to 0.89) were independent predictors. Fatal or near-fatal events defined as aborted cardiac arrest or sudden cardiac death occurred in 13 patients, resulting in an estimated 8-year event rate of 13%. Absence of β-blockers (HR, 5.54; 95% CI, 1.17 to 26.15) and history of aborted cardiac arrest (HR, 13.01; 95% CI, 2.48 to 68.21) were independent predictors. No difference was observed in cardiac and fatal or near-fatal event rates between probands and family members.
Conclusions— Cardiac and fatal or near-fatal events were not rare in both catecholaminergic polymorphic ventricular tachycardia probands and affected family members during the long-term follow-up, even while taking β-blockers, which was associated with a lower event rate. Further studies evaluating concomitant therapies are necessary to improve outcome in these patients.
Received October 17, 2008; accepted February 23, 2009.
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a familial arrhythmogenic disorder characterized by polymorphic ventricular tachyarrhythmias induced by physical or emotional stress without any detectable morphological abnormalities of the heart.1,2 Mutations in genes encoding cardiac ryanodine type 2 receptor (RYR2)3,4 and calsequestrin 2 (CASQ2)5,6 have been identified and are recognized as causing the autosomal-dominant and -recessive forms of CPVT, respectively. CPVT has become recognized as a significant cause of sudden cardiac death (SCD) in children and young adults, particularly in the era of molecular biology.7,8 Many clinical issues, however, remain to be clarified. For instance, the incidence of arrhythmic events occurring during β-blocker treatment varies among published reports.2,9–14 Likewise, little is known about the influence of prior cardiac symptoms or the patient’s age on the occurrence of tachyarrhythmias, and few data are available on the importance of family screening, including genetic examinations. To address these issues and to clarify the risk factors of cardiac events, we conducted a multicenter observational study and analyzed a large series of CPVT patients.
Clinical Perspective on p 2434
The patients enrolled were probands and family members referred to the study centers for genetic arrhythmias. Symptoms such as aborted cardiac arrest (ACA), syncope with or without seizures, and palpitations were investigated. Patients underwent a 12-lead ECG, 24-hour Holter ECG, 2-dimensional echocardiography, and an exercise stress test unless they had significant physical limitations. Exercise stress tests were performed with a Bruce protocol on a treadmill or as a graded, continuous test to maximal effort on a cycle ergometer. Intravenous catecholamines were administered if necessary. The diagnosis of CPVT was based on the criteria we previously published, which, in short, required stress-induced reproducible ventricular arrhythmias in patients with a normal resting ECG and no detectable structural heart abnormalities.2 Family screening was performed and blood samples were obtained from those who agreed to a genetic evaluation and provided written consent. The diagnosis of CPVT was made either on a clinical basis or after identification of a mutation in the RYR2 or CASQ2 gene. Patients with positive genetic results without any clinical symptoms or signs were defined as silent genetic mutation carriers.
None of the probands or family members reported in our previous publications1,2 were included. Twenty-eight patients from 8 families with RYR2 mutations11 and 6 patients from 2 families with CASQ2 mutations6 who were previously reported were included. Patients >55 years of age at the time of diagnosis were excluded to reduce the chance of including age-related events unlinked to CPVT.
Genomic DNA was extracted from peripheral blood leukocytes using standard methods. A targeted mutational analysis of 57 exons of the RYR2 gene was performed, covering areas with known function or mutations (exons 8 to 10, 14, 15, 22, 25, 27, 28, 29, 31, 34, 37, 38, 40 to 49, 51, 56, 59 to 64, 68, 70 to 73, 75, 83, 88 to 105). The coding regions were amplified with polymerase chain reaction and analyzed by denaturing high-performance liquid chromatography (WAVE, Transgenomic Inc, Omaha, Neb). Samples exhibiting abnormal profiles were analyzed by unidirectional sequencing with a 3100 BigDye Terminator version 3.1 sequencing kit and ABI PRISM 3100 Genetic Analyzer (Applied Biosystems, Foster City, Calif). All sequence variants were reamplified and resequenced to exclude polymerase errors. When putative mutations were detected, denaturing high-performance liquid chromatography analysis was performed on 200 samples (400 alleles) of genomic DNA from healthy and unrelated subjects to exclude DNA polymorphisms. In the patients without any identified mutations in the RYR2 gene, all 11 exons of the CASQ2 gene also were screened using intronic primers and analyzed by denaturing high-performance liquid chromatography.
After the diagnosis was confirmed, all patients (and their parents when appropriate) were strongly advised to avoid any strenuous physical activity according to the recommendations15 and were followed up every 6 to 12 months at the referring centers. The follow-up period was counted from the date of diagnosis to the date of the last visit or the patient’s death. The therapy, ie, drugs and implantable defibrillators (ICDs), depended on each individual physician. The dosage of the drug was determined from the patient’s body weight and was adjusted during follow-up. The incidence of cardiac events, defined as any syncope under physical or emotional stress, ACA, including appropriate ICD discharges, or SCD during follow-up, and the incidence of fatal or near-fatal events, defined as ACA or SCD, were evaluated. Risk factors of those events also were assessed.
Continuous variables, expressed as mean±SD, were compared by use of an unpaired t test; categorical variables were compared by use of Fisher’s exact test. The time to the first occurrence of a cardiac or fatal or near-fatal event was expressed visually with the use of Kaplan-Meier curves and assessed with the log-rank test when appropriate.16 The estimated 4- and 8-year event rates are presented. The time to event occurrence also was analyzed with Cox proportional-hazards models.17 Variables examined included gender, age at diagnosis, proband, cardiac symptoms before the diagnosis, identification of a mutation in the RYR2 or CASQ2 gene, silent genetic mutation carrier, and absence of β-blockers. A single-variable analysis was conducted first, and a multivariable analysis adjusted for variables with a single-variable value of P<0.20 was performed. Relative risks were expressed as hazard ratios (HRs) with 95% CIs. The data for patients who were lost to follow-up were analyzed up to the last contact. With regard to β-blockers, all analyses were performed according to the intention-to-treat principle. All probability values were based on 2-sided tests and were considered significant at P<0.05. All analyses were conducted with SPSS version 11.0 software (SPSS Inc, Chicago, Ill).
Characteristics of the Study Subjects
As of March 2008, 50 probands and 51 family members were enrolled. All probands and 34 family members were diagnosed on a clinical basis; the other 17 family members were silent genetic mutation carriers. Table 1 shows their baseline characteristics. The age at diagnosis was 15±10 years (range, 2 to 51 years). Cardiac symptoms before the diagnosis were reported in 61 patients (60%): in all probands and 11 family members. Among the 61 patients with symptoms before diagnosis, 57 patients (93%) were symptomatic before 21 years of age, and the diagnosis of CPVT was made with a delay of 2.6±4.4 years. In the present CPVT cohort, the rate of experiencing cardiac symptoms before the diagnosis was 35% and 72% at 10 and 20 years of age, respectively (Figure 1). Seizures were observed in 15 patients, 8 of whom were considered to have drug-resistant epilepsy until the diagnosis of CPVT. In 23 of the 40 family members without any prior cardiac symptoms, reproducible ventricular arrhythmias were recorded during exercise. During the exercise testing (n=91), ventricular tachycardia, couplets, and frequent isolated premature ventricular beats were induced in 27 (30%), 14 (15%), and 38 patients (42%), respectively. The exercise test was negative in 12 asymptomatic family members with a positive genotype (6 male patients; age, 18±14 years). These 12 patients and another 5 genetically affected asymptomatic family members who did not undergo exercise stress testing were considered silent genetic mutation carriers. Cardiac magnetic resonance imaging was performed in 3 patients, showing normal results.
Molecular analysis identified 28 different RYR2 and 3 different CASQ2 mutations (Figure 2). Forty-four probands underwent genetic screening, and RYR2 and CASQ2 mutations were found in 31 and 3, respectively. This screening yielded an overall rate of 77% for the detection of mutation even with a limited analysis of 57 exons of RYR2 gene. All family members included underwent a genetic examination, identifying mutant RYR2 and CASQ2 genes in 41 and 4, respectively.
Incidence of Cardiac and Fatal or Near-Fatal Events
During a follow-up of 7.9±4.9 years, 27 patients (27%) experienced cardiac events (Figure 3). The first cardiac event occurred 5.2±4.3 years after the diagnosis, and 10 of the 27 patients (37%) who had cardiac events during follow-up had events >1 (Table 2). The trigger of the first cardiac event was physical activity in 12 patients, emotional stress in 10, and unknown in 5, including 4 with SCD (Table 2). Fatal or near-fatal events developed in 13 of those 27 patients and were observed at between 13 and 26 years of age in 12 of the 13 patients (92%). A fatal or near-fatal event was the first event during follow-up in 9 patients, including 5 SCDs (Table 2). The estimated 4- and 8-year event rates for cardiac events were 12% and 32%, respectively, and those for fatal or near-fatal events were 4% and 13%, respectively (Figure 4A).
Cardiac events were observed in 15 probands and 12 family members, including 2 silent genetic mutation carriers with negative results on the exercise stress test, who were not treated with β-blockers. No difference was seen in the cardiac or fatal or near-fatal event rate between the probands and family members both in the total study population and in the subgroup of patients treated with β-blockers.
There were 37 asymptomatic patients with a positive genotype. During follow-up, cardiac events were observed in 9 of these 37 patients (24%) and in 18 of the other 64 patients (28%). No differences were observed in cardiac event rate (log-rank P=0.58) and fatal or near-fatal event rate (log-rank P=0.86) between these 2 groups.
β-Blockers were administered immediately after the diagnosis in 81 patients (80%) (Figure 3): nadolol in 63 and other β-blockers in 18. The most frequent reason that β-blockers were not prescribed was an absence of cardiac symptoms or stress-induced ventricular tachycardia; this was the case for 14 of the 20 untreated patients. In 8 patients, the physician changed the type of β-blocker because of insufficient drug efficacy during follow-up.
Among 81 patients on β-blockers, 62 (77%) experienced no events during follow-up (Figure 3). The other 19 patients experienced cardiac events, but at least 6 of them (32%) did not take the drug on the day of the event (Table 2). The estimated 4- and 8-year cardiac event rates were 8% and 27%, respectively, in the patients with β-blockers and 33% and 58%, respectively, in those without (log-rank P=0.01) (Figure 4B). Fatal or near-fatal events occurred in 9 of the 81 patients on β-blockers (11%), and at least 4 of the 9 patients (44%) did not take the drug on the day of the event. The estimated 4- and 8-year fatal or near-fatal event rates were 1% and 11%, respectively, in the patients with β-blockers and 18% and 25%, respectively, in those without (log-rank P=0.05) (Figure 4C).
Nadolol was used with a latest dosage of 1.6±0.9 mg/kg. Cardiac events during follow-up were observed in 12 of 63 patients (19%) with nadolol and in 7 of 18 patients (39%) with β-blockers other than nadolol. In 2 of 3 patients experiencing SCD on nadolol, the dosage at that time was <1.0 mg/kg (Table 2).
Risk Factors of Cardiac and Fatal or Near-Fatal Events
Table 3 shows the predictors for cardiac and fatal or near-fatal events using a Cox proportional-hazards analysis. A multivariable analysis revealed that younger age at the time of diagnosis (HR, 0.54 per decade; 95% CI, 0.33 to 0.89; P=0.02) and absence of β-blockers (HR, 5.48; 95% CI, 1.80 to 16.68; P=0.003) were independent predictors for cardiac events. In addition, a history of ACA before the diagnosis (HR, 13.01; 95% CI, 2.48 to 68.21; P=0.002) and absence of β-blockers (HR, 5.54; 95% CI, 1.17 to 26.15; P=0.03) were independent predictors for fatal or near-fatal events. Syncopal history before the diagnosis was not associated with higher cardiac or fatal or near-fatal event rates.
In the subgroup of 81 patients receiving β-blockers, β-blockers other than nadolol (HR, 3.12; 95% CI, 1.16 to 8.38; P=0.02) and younger age at diagnosis (HR, 0.31 per decade; 95% CI, 0.14 to 0.69; P=0.004) were independent predictors for cardiac events.
Therapies Other Than β-Blockers
Verapamil was added to the β-blockers in 4 patients, who remained event free during the next 1.6±0.6 years. An ICD was implanted immediately after diagnosis in 4 patients and 5.8±4.2 years after diagnosis in 12 patients because of syncope in 6, ACA in 2, and ventricular arrhythmias provocable during the exercise stress test despite β-blocker therapy in 4. The age at the ICD implantation was 20±11 years (8 male and 8 female patients). In all patients, the ICD was initially programmed with 1 ventricular fibrillation zone with a detection interval of <300 ms. Among 16 patients with an ICD, appropriate shocks were delivered in 4 patients (25%), and inappropriate shocks were noted in 6 patients (38%): resulting from sinus tachycardia in 4 and lead fractures in 2. The follow-up period after the diagnosis in the patients with an ICD was 9.0±4.4 years, and no patients died during 3.9±2.8 years of follow-up after the ICD implantation.
Exercise Stress Tests During the Follow-Up
Data from the exercise stress test during the follow-up were obtained in 70 patients: 1, 2, and ≥3 tests in 11, 29, and 30 patients, respectively. The tests were performed with a treadmill or ergometer in 33 and 37 patients, respectively. Cardiac events developed in 21 of the 70 patients (30%). The latest results, which were the results just before the cardiac events in the patients experiencing them, were couplets or more successive premature ventricular contractions in 13 of the 21 patients with cardiac events and 16 of the 49 patients without (62% versus 33%; sensitivity, 0.62; specificity, 0.67; P=0.03). Other arrhythmias provoked were not significantly associated with future cardiac events.
The analysis of 101 CPVT patients followed up for 7.9±4.9 years showed that cardiac events developed in 27 patients (27%), including 13 patients with fatal or near-fatal events (13%), which gave an estimate for the 8-year cardiac and fatal or near-fatal event rates of 32% and 13%, respectively. In most of the patients (12 of the 13 patients [92%]), a fatal or near-fatal event occurred at between 13 and 26 years of age. In the multivariable analyses, absence of therapy with any β-blockers was an independent predictor for cardiac events, as well as younger age at the time of the diagnosis, and was an independent predictor for fatal or near-fatal events, as well as a history of ACA. No difference was observed in the cardiac or fatal or near-fatal event rate between the probands and family members, between the patients with and without a prior syncopal event, or between the asymptomatic patients with a positive genotype and the other patients.
Incidence of Arrhythmias
In studies2,9–14 following up >10 CPVT patients, the occurrence of cardiac events varied from 2% to 62% of the subjects (Table 4). Those reports included both probands and family members, and most patients received β-blockers. The difference in the incidence of cardiac events between the present study and others may be attributable to the difference in the type, dosage, or compliance with β-blockers and possibly to the small number of subjects in the studies published so far. Those studies2,9,10,12–14 followed up <50 patients, except for 1 study11 that included 54 patients with only 1 patient experiencing a cardiac event during a median follow-up of 2 years. A longer follow-up period, however, may be necessary to ascertain the occurrence of cardiac events in CPVT because the first cardiac event occurred 5.2±4.3 years after diagnosis in the present study.
The present study also demonstrated that syncopal history before diagnosis was not associated with higher cardiac or fatal or near-fatal event rates during the follow-up, although history of ACA was an independent predictor for fatal or near-fatal events (Table 3). This result should be taken into consideration for risk stratification in patients diagnosed with CPVT. We think that β-blockers should be prescribed in every CPVT patient regardless of any prior syncopal events.
Effectiveness of β-Blockers
β-Blockers have empirically been considered the best therapeutic option in CPVT,1,2 but to the best of our knowledge, no study has compared event rates between patients with and without β-blockers. In the present study, we confirmed significantly lower cardiac and fatal or near-fatal event rates in the patients with β-blockers. Nonetheless, the 8-year cardiac and fatal or near-fatal event rates in the patients with β-blockers were not sufficiently low (27% and 11%, respectively). This incomplete effect of β-blockers may be attributable, at least in part, to poor drug compliance, which was observed in some patients experiencing those events and was shown in our previous report.2 Physicians must keep patients aware that missing even a single dose can provoke lethal arrhythmias. The type of β-blockers also could have influenced the outcome. Although treatment was not randomized, the present study suggests that taking β-blockers other than nadolol could be associated with higher event rates. It is noteworthy that, in 3 of 5 SCDs occurring in patients taking nadolol, 2 patients took a low dosage (Table 2). These results suggest that nadolol is a recommendable drug for CPVT patients when used with a sufficient dosage (>1.5 mg/kg). Furthermore, incomplete drug therapy may be attributable to the absence of reliable tests to ascertain its efficacy. Results of exercise stress tests during follow-up were significantly associated with future cardiac events, but the sensitivity and specificity were not sufficiently high, suggesting that the exercise stress test can be used only as a moderate guide for therapy efficacy, although it is useful for diagnosing CPVT.1,2,9,11–14
Therapeutic Option Added to β-Blockers
Two studies18,19 reported that verapamil added to β-blockers suppressed ventricular arrhythmias in the CPVT patients during the exercise stress test, suggesting its beneficial effect in combination with β-blockers. ICDs can be another therapeutic option despite the potential drawbacks in young patients20 and concern about provoking arrhythmic storms.21 A recent case series22 also showed the efficacy of left cardiac sympathetic denervation, which was not performed in any patients in the present study. We could not assess the role of verapamil because of the small number of patients treated with this drug. Further studies are necessary to elucidate the clinical efficacy of those therapeutic options in CPVT. The results of the present study suggest that those additional therapies should be discussed, especially for young patients, those with history of ACA, or those with poor β-blocker efficacy or compliance.
To the best of our knowledge, no study has separately evaluated the incidence of arrhythmic events between probands and family members. We found a similar event rate in analyses both with and without adjustment for the treatment with β-blockers; we also observed, as others9 did, that cardiac events occurred in silent genetic mutation carriers with normal exercise stress tests. These results underline the importance of family screening, including genetic testing, and strongly suggest that genetically positive family members should receive β-blockers even after a negative exercise test, which can change with time.9,14
Age and Risk of Arrhythmias
The present study demonstrated that a younger age at the CPVT diagnosis was an independent predictor of future cardiac events. The background of the relationship between age and arrhythmia risk is uncertain and probably multifactorial. It is speculated that children have more opportunities to engage in strenuous physical activities or to become excited and that patients with more severe forms of CPVT, barely suppressed by drugs, are diagnosed younger in life. Furthermore, β-blocker dosage based on weight might be insufficient in children because many hepatically eliminated drugs, including β-blockers, show an age-dependent clearance.
This study has several limitations. First, the therapeutic management depended on each individual physician, and the administration of β-blockers was not randomized. However, it seems ethically difficult not to prescribe β-blockers in the CPVT patients. Even in patients with an ICD, β-blockers should not be discontinued because ICDs do not always terminate CPVT.21 Second, because of the small number of patients (n=19) and the short subsequent follow-up period (3.1±2.5 years), we could not draw any definitive conclusions regarding the management of patients after cardiac events under β-blockers. Third, enrollment of family members in the present study was subject to potential bias because family screening based on voluntary participation was not thoroughly performed.
CPVT is a malignant channelopathy with high cardiac and fatal or near-fatal event rates in both probands and affected family members. Prescription of β-blockers is associated with lower event rates but does not provide sufficient prevention of arrhythmias. Further studies evaluating the indications and efficacy of concomitant therapies, ie, verapamil, ICDs, or left cardiac sympathetic denervation, are necessary to improve outcome in these patients at high risk for SCD.
We sincerely thank all the patients enrolled in the study and the following persons for their important contributions: T. Benali, M. Berthet, J.J. Blanc, A. Chantepie, A. Da Costa, D. Do Ngoc, A.K. Duke, Y. Dulac, J.M. Dupuis, S. Falcon-Eicher, P. Gaudeul, F. Godart, X. Hernandorena, G. Karsenty, G. Kirkorian, C. Kouakam, A. Legendre, V. Lucet, S. Maugenre, S. Magnier, D. Magnin, P. Maragnes, J. Martin, M. Massin, A. Mathiron, O. Navarre, G. Pavin, A. Postoma, D. Raguin, P.P. Samaille, P. Scanu, C. Sebac, N. Shannon, M. Shkolnikova, T. Sluysmans, G. Vaksmann, J. Victor, and A. Çeliker.
Source of Funding
The authors received a grant from the French national government named Programme Hospitalier de Recherche Clinique No. AOR04070, P040411.
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Catecholaminergic polymorphic ventricular tachycardia is a rarely recognized but important cause of sudden cardiac death in the young. This multicenter observational study of 101 subjects (50 probands, 51 family members) was conducted to characterize the clinical course of the disease. Catecholaminergic polymorphic ventricular tachycardia was diagnosed from clinical features in 84 subjects and from genotyping in 17 subjects. During the follow-up of 7.9±4.9 years, 27 patients (27%), including 2 silent gene mutation carriers, experienced syncope, aborted cardiac arrest, or sudden cardiac death events that were fatal or near-fatal in 13 subjects. The estimated 8-year event rate was 32% with a 13% rate of fatal or near-fatal events. The event rates between the probands and family members were comparable. A younger age at diagnosis, a history of aborted cardiac arrest, and the absence of β-blockers were predictors of events, but β-blocker therapy was not completely protective. These results suggest that β-blockers should be prescribed even if the diagnosis is made from genotyping when there is not a history of symptomatic arrhythmias. Additional therapies, including implantable defibrillators, verapamil, or left cardiac sympathetic denervation, should be considered in patients with markers of increased risk.