Mechanisms of sustained ventricular tachycardia in myotonic dystrophy: implications for catheter ablation

[When do you implant a pacemaker in myotonic dystrophy?]

Myotonic dystrophy is the most frequent adult form of hereditary muscular dystrophy caused by a mutation on the DMPK gene. Myotonic dystrophy leads to multiple systemic complications related to weakness, respiratory failure, cardiac arrhythmias and cardiac conduction disturbances. Age of death is earlier in myotonic dystrophy patients than in general population with a high frequency of sudden death. Several mechanisms are involved in sudden death: atrio-ventricular block, severe ventricular arrhythmias or non-cardiac mechanism. The high degree of atrio-ventricular block is a well-recognized indication of pacemaker implantation but the prophylactic implantation of pacemaker should be considered to prevent sudden death in asymptomatic myotonic dystrophy patients. A careful clinical evaluation needs to be done for the identification of patients at high risk of sudden death. The resting ECG and SA ECG are non-invasive tools useful to select the patients who need an electrophysiologic study. In presence of prolonged HV interval more than or equal to 70 ms one can discuss the implantation of a prophylactic pacemaker. The choice of an implantable cardiac defibrillator is preferred in presence of spontaneous ventricular tachycardia or an alteration of the left ventricular ejection fraction.

A novel KCNQ1 variant (L203P) associated with torsades de pointes-related syncope in a Steinert syndrome patient

BACKGROUND

A 43-year-old woman suffering from Steinert syndrome was admitted after experiencing multiple episodes of torsades de pointes-related syncope.

OBJECTIVES

To elucidate the pathophysiology of these arrhythmic events.

METHODS AND RESULTS

We obtained DNA from the patient and sequenced the coding region of KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 genes. A single nucleotide change was identified in the KCNQ1 gene at position 608 (T608C), resulting in a substitution from leucine to proline at position 203 (L203P). CHO cells were used to express either wild-type KCNQ1, wild-type KCNQ1+L203P KCNQ1 (50:50), or L203P KCNQ1, along with KCNE1 to recapitulate the slow cardiac delayed rectifier potassium current (I(Ks)). Patch-clamp experiments showed that the variant L203P causes a dominant negative effect on I(Ks). Coexpression of wild-type KCNQ1 and L203P KCNQ1 (50:50) caused a ~75% reduction in current amplitude when compared to wild-type KCNQ1 alone (131.40 ± 23.27 vs 567.25 ± 100.65 pA/pF, P < .001). Moreover, when compared with wild-type KCNQ1 alone, the coexpression of wild-type KCNQ1 and L203P KCNQ1 (50:50) caused a 7.5-mV positive shift of midpoints of activation (from 27.5 ± 2.4 to 35.1 ± 1.2 mV, P < .05). The wild-type KCNQ1 and L203P KCNQ1 (50:50) coexpression also caused alteration of I(Ks) kinetics. The activation kinetics of the L203P variant (50:50) were slowed compared with wild-type KCNQ1, while the deactivation kinetics of L203P (50:50) were accelerated compared with wild type, all these further contributing to the "loss-of-function" phenotype of I(Ks) associated with the variant L203P.

CONCLUSION

Torsades de pointes and episodes of syncope are very likely to be due to the KCNQ1 variant L203P found in this patient.

Increased temporal dispersion of myocardial repolarization in myotonic dystrophy type 1: beyond the cardiac conduction system

BACKGROUND AND OBJECTIVES

The most frequently mechanism underlying sudden cardiac death in myotonic dystrophy type 1 (DM1) is bradyarrhythmias due to cardiac conduction abnormalities. However the risk of ventricular tachyarrhythmias remains a concern in clinical management as well as in its determinant. We therefore assessed autonomic nervous system activity aiming to disclose differences in the QT variability index (QTVI)-a marker of temporal myocardial repolarization lability-between DM1 patients and healthy controls. We also investigated the possible differences within DM1 patients by subdividing them according either to the presence of first degree atrioventricular block (1st AVB) or to the cytosine-thymine-guanine (CTG) repeat expansion size.

METHODS

Sixty-two DM1 patients and 20 healthy subjects underwent neurological and cardiological examinations, the latter including ECG, echocardiography and 24-hour Holter monitoring. All underwent a 5-minute ECG recording to assess heart rate variability power spectral components, and the QTVI values.

RESULTS

Power spectral data, namely total power, low frequency power and high frequency power, were lower, whereas QTVI values were higher in DM1 patients than in controls (p<.0001). Higher QTVI values were found in DM1 subgroups with 1st AVB (p=.009) and more than 500 CTG repeat (p=.014) with respect to DM1 patients without 1st AVB and CTG<500. Spectral data did not significantly differ. At multivariable analysis, QTVI and age were independently associated with PR interval and CTG repeat.

CONCLUSIONS

The increased values of QTVI argue in favour of an important heart involvement extending beyond the conduction system. Whether QTVI could be useful in predicting clinical course of DM1 clearly requires larger prospective studies.

Ventricular tachycardia and ventricular fibrillation

Ventricular tachycardia and ventricular fibrillation are the most important causes of sudden cardiac death (SCD), particularly in those with structural heart disease and reduced left ventricular function. It is important to distinguish ventricular tachycardia from supraventricular tachycardia. A wide spectrum of ventricular arrhythmias exists, from those where the heart is structurally normal to those with structural heart disease. Each entity has a distinctive pathophysiology, treatment plan and prognostic outcome. Treatment modalities include simple beta-blockade to implantation of implantable cardiac defibrillator and ablative approaches. In general, those ventricular arrhythmias associated with a structurally normal heart are more benign than those associated with structural heart disease.

Risk of arrhythmias in myotonic dystrophy: trial design of the RAMYD study

OBJECTIVE

Myotonic dystrophy type 1 (DM1) is the most frequent muscular dystrophy in adults. DM1 is a multisystem disorder also affecting the heart with an increased incidence of sudden death, which has been explained with the common impairment of the conduction system often requiring pacemaker implantation; however, the occurrence of sudden death despite pacemaker implantation and the observation of major ventricular arrhythmias generated the hypothesis that ventricular arrhythmias may play a causal role as well. The aim of the study was to assess the 2-year cumulative incidence and the value of noninvasive and invasive findings as predictive factors for sudden death, resuscitated cardiac arrest, ventricular fibrillation, sustained ventricular tachycardia and severe sinus dysfunction or high-degree atrioventricular block.

METHODS/DESIGN

More than 500 DM1 patients will be evaluated at baseline with a clinical interview, 12-lead ECG, 24-h ECG and echocardiogram. Conventional and nonconventional indications to electrophysiological study, pacemaker, implantable cardioverter defibrillator or loop recorder implantation have been developed. In the case of an indication to electrophysiological study, pacemaker, implantable cardioverter defibrillator or loop recorder implant at baseline or at follow-up, the patient will be referred for the procedure. At the end of 2-year follow-up, all candidate prognostic factors will be tested for their association with the endpoints.

TRIAL REGISTRATION

ClinicalTrials.gov ID NCT00127582.

CONCLUSION

The available evidence supports the hypothesis that both bradyarrhythmias and tachyarrhythmias may cause sudden death in DM1, but the course of cardiac disease in DM1 is still unclear. We expect that this large, prospective, multicenter study will provide evidence to improve diagnostic and therapeutic strategies in DM1.

Sudden death in Steinert's disease

Steinert's disease is an autosomal dominant neuromuscular disorder. Heart involvement is characterized by conduction system abnormalities, supraventricular and ventricular arrhythmias. Patients with Steinert's disease are reported to have a higher incidence of sudden death. Preventing sudden death is crucial in this disease. It relies on non-invasive and/or invasive approach for risk stratification.

Usefulness of clinical and electrocardiographic data for predicting adverse cardiac events in patients with myotonic dystrophy

BACKGROUND

Myotonic dystrophy type 1 (DM1) has been associated with an increased risk of sudden death, either by heart block or malignant ventricular arrhythmias. Identifying patients at risk remains difficult and no consensus has been reached regarding the best approach for follow-up and prevention of sudden death.

OBJECTIVES

To identify noninvasive clinical and electrocardiographic predictors of adverse cardiac events in patients with DM1.

METHODS

Clinical and serial electrocardiographic data on 428 patients with a DNA-proven diagnosis of DM1, followed during a mean period of 11.7 years, were reviewed. Variables associated with adverse cardiac events were identified.

RESULTS

Eleven patients (2.6%) experienced sudden death and 13 (3.0%) required implantation of a pacemaker. On univariate analysis, adverse events were associated with advancing age, prolongation of the PR, QRS and corrected QT (QTc) intervals, as well as the degree of neuromuscular impairment. No such relationship was found with the extent of genetic anomaly (number of cytosine-thymine-guanine repeats). However, multivariate analysis using Cox proportional hazards models showed that only baseline PR and QTc intervals were significantly linked to the end points of sudden death or pacemaker implantation; the age-adjusted RR was 3.7 (95% CI 1.5 to 8.6) if baseline PR was 200 ms or longer (P=0.003), and 3.0 (95% CI 1.0 to 8.8) if the baseline QTc was 450 ms or longer (P=0.047).

CONCLUSIONS

In a large unselected cohort of 428 patients with DM1, the cumulative incidence of sudden death was relatively low, and the delayed conduction on surface electrocardiogram was found to be potentially helpful for identifying patients at risk for sudden death or pacemaker implantation.

Electrocardiographic abnormalities and sudden death in myotonic dystrophy type 1

BACKGROUND

Sudden death can occur as a consequence of cardiac-conduction abnormalities in the neuromuscular disease myotonic dystrophy type 1. The determinants of the risk of sudden death remain imprecise.

METHODS

We assessed whether the electrocardiogram (ECG) was useful in predicting sudden death in 406 adult patients with genetically confirmed myotonic dystrophy type 1. A patient was characterized as having a severe abnormality if the ECG had at least one of the following features: rhythm other than sinus, PR interval of 240 msec or more, QRS duration of 120 msec or more, or second-degree or third-degree atrioventricular block.

RESULTS

Patients with severe abnormalities according to the entry ECG were older than patients without severe abnormalities, had more severe skeletal-muscle impairment, and were more likely to have heart failure, left ventricular systolic dysfunction, or atrial tachyarrhythmia. Such patients were more likely to receive a pacemaker or an implantable cardioverter-defibrillator during the follow-up period. During a mean follow-up period of 5.7 years, 81 patients died; there were 27 sudden deaths, 32 deaths from progressive neuromuscular respiratory failure, 5 nonsudden deaths from cardiac causes, and 17 deaths from other causes. Among the 17 patients who died suddenly in whom postcollapse rhythm was evaluated, a ventricular tachyarrhythmia was observed in 9. A severe ECG abnormality (relative risk, 3.30; 95% confidence interval [CI], 1.24 to 8.78) and a clinical diagnosis of atrial tachyarrhythmia (relative risk, 5.18; 95% CI, 2.28 to 11.77) were independent risk factors for sudden death.

CONCLUSIONS

Patients with adult myotonic dystrophy type 1 are at high risk for arrhythmias and sudden death. A severe abnormality on the ECG and a diagnosis of an atrial tachyarrhythmia predict sudden death. (ClinicalTrials.gov number, NCT00622453.)

Modelling of the ventricular conduction system

The His-Purkinje conduction system initiates the normal excitation of the ventricles and is a major component of the specialized conduction system of the heart. Abnormalities and propagation blocks in the Purkinje system result in abnormal excitation of the heart. Experimental findings suggest that the Purkinje network plays an important role in ventricular tachycardia and fibrillation, which is the major cause of sudden cardiac death. Nowadays an important area in the study of cardiac arrhythmias is anatomically accurate modelling. The majority of current anatomical models have not included a description of the Purkinje network. As a consequence, these models cannot be used to study the important role of the Purkinje system in arrhythmia initiation and maintenance. In this article we provide an overview of previous work on modelling of the Purkinje system and report on the development of a His-Purkinje system for our human ventricular model. We use the model to simulate the normal activation pattern as well as abnormal activation patterns resulting from bundle branch block and bundle branch reentry.

Cardiovascular manifestations of myotonic dystrophy-1

Myotonic dystrophy (DM) is an inherited disorder transmitted in an autosomal dominant fashion and characterized by myotonia with dystrophic involvement of muscles and other multisystemic manifestations. It is the most common muscular dystrophy in whites. DM1, the most common type of DM, is associated with conduction defects, tachyarrhythmia, cardiomyopathy, and other cardiac disorders such as valvular diseases. The conduction defects in patients with DM1 are progressive; therefore, these patients should undergo careful work-up and follow-up, even if presenting with a benign conduction defect such as first-degree atrioventricular block. Atrial tachyarrhythmias are the most common arrhythmias in DM1, although ventricular tachycardia (VT) with a bundle branch re-entry mechanism can also occur. Interestingly, such VT can be cured by right bundle branch ablation with no need for an implantable cardioverter defibrillator. A significant portion of DM1 patients have heart failure, which is not clinically apparent, in part, because of the limited ability for exertion. Therefore, a low threshold should be used regarding when evaluating the heart by echocardiogram. Cardiovascular manifestations of DM1 have several important aspects that require careful attention and knowledge of the current evidence to make the best treatment decision. This article reviews the relevant DM1 literature and provides suggestions for diagnosis and treatment of patients with DM1.

Bundle Brunch Reentrant Ventricular Tachycardia with Two Distinct Conduction Patterns in a Patient with Complete Right Bundle Branch Block

We report a rare case of bundle branch reentrant ventricular tachycardia [BBRVT]. A 67-year-old female was admitted for management of wide QRS tachycardia (right bundle branch block [RBBB] and a southwest axis). The mapping procedure revealed the tachycardia circuit consisted of the left anterior fascicle (LAF) as an antegrade, and the right bundle as a retrograde pathway. She presented RBBB during sinus rhythm. LAF ablation changed the tachycardia configuration to a northwest axis and prolonged the cycle length. Left posterior fascicle ablation terminated the tachycardia, and complete atrioventricular block occurred, which showed the unidirectional conduction over the right bundle.

Heart Rate Turbulence as a Noninvasive Risk Predictor of Ventricular Tachyarrhythmias in Myotonic Dystrophy Type 1

INTRODUCTION

Myotonic dystrophy type 1 (MD1) is the most common muscular dystrophy of adult life. Cardiac involvement is characterized by disorders of atrioventricular conduction, ventricular arrhythmias, and sudden death. Heart rate turbulence (HRT) is a noninvasive risk predictor in patients affected by ischemic heart disease. The aim of our study is to assess the prognostic value of HRT in MD1 patients.

METHODS AND RESULTS

We performed HRT analysis by 24-hour Holter recording to calculate turbulence onset (TO) and turbulence slope (TS) in 29 MD1 patients (mean age 52 +/- 10 years), and in 30 patients (mean age 52 +/- 13 years) with frequent ventricular arrhythmias and structurally normal heart (VANH). An electrophysiological study (EPS) tested ventricular arrhythmias inducibility in 22 MD1 patients. TO was significantly different between MD1 and VANH patients (-1.66 +/- 2.04 and -2.98 +/- 1.79%, respectively, P 0.01), while no difference was observed in TS between MD1 and VANH patients (11.12 +/- 6.46 and 9.12 +/- 6 msec/beat, respectively). On EPS, sustained ventricular arrhythmias (SVA) were induced in six MD1 patients. TO was significantly different in inducible MD1 patients (0.88 +/- 1.95%), as compared with both noninducible (-2.49 +/- 1.43%, P < 0.001) or no eligible to EPS (-1.93 +/- 1.63%, P < 0.005) MD1 patients and to VANH patients (-2.98 +/- 1.79%, P < 0.001).

CONCLUSIONS

An impairment of TO, a measure of HRT, suggesting impaired cardiac parasympathetic activity, may be a useful, noninvasive predictor of arrhythmic risk in MD1 patients.

Bundle branch reentrant tachycardia in a patient with a calcified bicuspid aortic valve and normal ventricular function

We report the case of a bundle branch reentrant tachycardia (BBRT) in a 40-yearold patient with a calcified bicuspid aortic valve and normal left ventricular function. The ventricular tachycardia was eliminated by successful radiofrequency ablation of the right bundle branch. As the aortic valve annulus is in close proximity to the specialized conduction system, premature degeneration of a bicuspid aortic valve may involve the bundle of His and the proximal bundle branches by invading calcifications. We speculate that calcifications invading the proximal bundle branches from the bicuspid aortic valve may have created the substrate for the BBRT in this patient.

Widespread Electroanatomic Alterations of Right Cardiac Chambers in Patients with Myotonic Dystrophy Type 1

INTRODUCTION

Conduction disturbances and arrhythmias characterize the cardiac feature of myotonic dystrophy type 1 (MD1); a myocardial involvement has been suggested as part of the cardiac disease. The aim of our study was to investigate the underlying myocardial alterations using electroanatomic mapping (CARTO) and their possible correlation with genetic and neurological findings.

METHODS AND RESULTS

Right atrial and ventricular CARTO maps were obtained in 13 MD1 patients. Thirteen age-matched patients with paroxysmal supraventricular tachycardia and normal heart served as controls. Unipolar voltage (UNI-v), bipolar voltage (BI-v) amplitudes, bipolar potential duration (Bi-dur), and atrial propagation time (A-pt) were measured. UNI-v and BI-v in interatrial septum, anterolateral atrial wall, and right ventricle outflow tract were lower in MD1 patients than controls (P < 0.001). Bi-dur and A-pt were longer in MD1 patients than controls (P < 0.001, P = 0.046, respectively). A significant relationship was documented between CTG triplets and the percentage of Bi-v <0.5 mV in the atrial anteroseptal region (r = 0.6, P = 0.02).

CONCLUSIONS

Altered electroanatomic patterns are present in the right cardiac chambers in MD1 patients. Widespread myocardial alterations, not necessarily limited to the conduction system, may support the presence of a cardiac myopathy as part of the disease.

Familial clustering of muscular and cardiac involvement in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is associated with both skeletal and cardiac muscle involvement. The aim of the present study was to determine whether familial clustering is observed in the severity of muscle involvement in DM1. We evaluated 51 sibling groups constituting 112 patients with genetically-verified DM1. The siblings were similar to each other in age, cytosine-thymine-guanine (CTG) repeat length, age at disease onset, muscular impairment rating score, and electrocardiographic markers of cardiac conduction disease. After adjusting for the similarities between siblings in age and CTG repeat length, the siblings remained similar to each other in measures of both skeletal and cardiac muscle involvement. These results suggest that factors other than CTG repeat length play a role in the severity and progression of the degenerative skeletal and cardiac muscle disease in DM1.

Cardiac function tests in neuromuscular diseases

Myocardial involvement is a known complication of neuromuscular diseases and is a leading cause of morbidity and mortality in these disorders. Identifying patients early using cardiac function tests helps understand the mechanisms underlying cardiac involvement and may help limit the progression of cardiac disease before the onset of significant symptoms and limitation. This article outlines the tests available to assess cardiac involvement associated with neuromuscular diseases and offers guidelines for management once they are discovered.

Myotonic dystrophy: RNA pathogenesis comes into focus

Myotonic dystrophy (DM)--the most common form of muscular dystrophy in adults, affecting 1/8000 individuals--is a dominantly inherited disorder with a peculiar and rare pattern of multisystemic clinical features affecting skeletal muscle, the heart, the eye, and the endocrine system. Two genetic loci have been associated with the DM phenotype: DM1, on chromosome 19, and DM2, on chromosome 3. In 1992, the mutation responsible for DM1 was identified as a CTG expansion located in the 3' untranslated region of the dystrophia myotonica-protein kinase gene (DMPK). How this untranslated CTG expansion causes myotonic dystrophy type 1(DM1) has been controversial. The recent discovery that myotonic dystrophy type 2 (DM2) is caused by an untranslated CCTG expansion, along with other discoveries on DM1 pathogenesis, indicate that the clinical features common to both diseases are caused by a gain-of-function RNA mechanism in which the CUG and CCUG repeats alter cellular function, including alternative splicing of various genes. We discuss the pathogenic mechanisms that have been proposed for the myotonic dystrophies, the clinical and molecular features of DM1 and DM2, and the characterization of murine and cell-culture models that have been generated to better understand these diseases.

Mechanisms underlying ventricular arrhythmias in idiopathic dilated cardiomyopathy: implications for management

Ventricular arrhythmias (VA) have been associated with mortality in idiopathic dilated cardiomyopathy (IDCM). All 3 main mechanisms of arrhythmogenesis - reentry, trigger activity, and automatism - have been implicated. Arrhythmogenic substrates in IDCM favor these mechanisms and are often potentiated by electrolyte imbalance secondary to diuretic treatment, by antiarrhythmic drugs, or by bradycardia, leading to polymorphic ventricular tachycardia (VT). Myocardial macroreentry is the mechanism most frequently responsible for monomorphic VT in IDCM; however, focal activation and His-Purkinje macroreentry are often responsible and, especially in the latter case, are frequently unrecognized. Clinical suspicion and final recognition by electrophysiologic testing have important therapeutic consequences, because both focal activation and His-Purkinje macroreentry can be treated effectively by catheter ablation. On the other hand, the frequent recurrences of myocardial macroreentrant VT after ablation require this therapy to be used in combination with drugs or an implantable cardioverter defibrillator (ICD). beta-Adrenoceptor antagonists (beta-blockers) have a beneficial effect for primary prevention of VA in IDCM. Type III antiarrhythmics have a neutral effect on mortality and type I antiarrhythmics should be avoided. Treatment of nonsustained VT in IDCM is controversial because it often presents without symptoms and is linked more to overall mortality than to arrhythmic mortality. Empiric treatment with amiodarone or electrophysiologically guided sotalol are preferred to the use of other drugs for secondary prevention of sustained VA. ICDs should be implanted in patients who have been resuscitated from cardiac arrest due to VA, or in those with poorly tolerated VT and severe left ventricular dysfunction. Empiric treatment with amiodarone or electrophysiologically guided class III antiarrhythmics may also be alternatives for patients with IDCM and no severe left ventricular dysfunction, especially if VT is well tolerated.

Prevalence of structural cardiac abnormalities in patients with myotonic dystrophy type I

BACKGROUND

Myotonic dystrophy type 1 (DM1) is a neurological disorder with known cardiac involvement, including conduction disturbances, arrhythmias, and ventricular dysfunction. We studied which clinical and electrocardiographic features are associated with structural cardiac abnormalities.

METHODS

History, physical examination, electrocardiography, and genetic testing were performed on 382 patients with DM1, and cardiac imaging was performed on 100 of these patients.

RESULTS

Clinical congestive heart failure was found in 7 of the 382 patients (1.8%). Structural cardiac abnormalities determined with cardiac imaging included left ventricular hypertrophy (19.8%), left ventricular dilatation (18.6%), left ventricular systolic dysfunction (14.0%), mitral valve prolapse (13.7%), regional wall motion abnormality (11.2%), and left atrial dilatation (6.3%). Left ventricular systolic dysfunction was associated with increasing age (relative risk [RR], 1.9 per decade; 95% CI, 1.1-3.2; P =.02), cytosine-thymine-guanine (CTG) repeat length (RR, 2.8 per 500 repeats; 95% CI, 1.3-6.3; P =.01), P-R >200 ms (RR, 14.7; 95% CI, 3.0-73.1; P =.001), and QRS >120 ms (RR, 5.7; 95% CI, 1.5-21.8; P =.01). P-R >200 ms was predictive of regional wall motion abnormalities. QRS >120 ms correlated with regional wall motion abnormalities and left atrial dilatation.

CONCLUSIONS

Several clinical and electrocardiographic findings in patients with DM1 are significantly associated with structural heart abnormalities. These results suggest an underlying genetic and pathophysiologic correlate that may lead to cardiac disease in these patients.

Long-term follow-up of arrhythmias in patients with myotonic dystrophy treated by pacing: a multicenter diagnostic pacemaker study

OBJECTIVES

We hypothesized that pacemaker (PM) implantation in patients with myotonic dystrophy (MD) with a prolonged HV interval, even asymptomatic, may protect them against sudden death related to atrioventricular (AV) block. We sought to prospectively document the true incidence of AV block episodes in this high-risk population and accurately trace, in the long term, by the PM, the occurrence of arrhythmias that may remain undetected during conventional follow-up.

BACKGROUND

Myotonic dystrophy is associated with a high risk of sudden death, commonly attributed to AV block or ventricular arrhythmias, but cardiac pacing is only recommended as a secondary prevention.

METHODS

Patients with MD with an HV interval > or =70 ms, even in the absence of related symptoms, prospectively received a cardiac PM, including an algorithm capable of diagnosing episodes of bradycardia and tachyarrhythmias.

RESULTS

The population consisted of 49 patients (45.5 +/- 8.9 years old) followed for 53.5 +/- 27.2 months. Paroxysmal arrhythmias were recorded in 41 patients (83.7%), consisting of complete AV block (n = 21), sino-atrial block (n = 4), or atrial (n = 25) or ventricular (n = 13) tachyarrhythmias. No patient died of AV block during follow-up, but 10 deaths occurred, 4 of them sudden. An arrhythmic cause could be excluded by postmortem PM interrogation in two cases of typical sudden death.

CONCLUSIONS

Arrhythmias are common in patients with MD with infrahisian conduction abnormalities. The prophylactic implantation of a pacing system when the HV interval is > or =70 ms seems appropriate. The PM protects the patient against the clinical consequences of paroxysmal profound bradycardia and facilitates the diagnosis and management of frequent paroxysmal tachyarrhythmias.

[Myotonic dystrophy and bundle-branch re-entrant tachycardia]

We report the case of a 37-year-old man diagnosed with myotonic dystrophy who presented atrial fibrillation with high ventricular rate. While being treated with amiodarone, he suffered cardiac arrest. The electrophysiological study disclosed bundle-branch reentrant ventricular tachycardia and ventricular fibrillation. Catheter ablation of the right bundle branch was performed and a bicameral defibrillator was implanted. The mechanisms and treatment of arrhythmias in these patients are discussed.

Does cytosine-thymine-guanine (CTG) expansion size predict cardiac events and electrocardiographic progression in myotonic dystrophy?

OBJECTIVE

To assess whether the size of the cytosine-thymine-guanine (CTG) expansion mutation in myotonic dystrophy predicts progression of conduction system disease and cardiac events.

DESIGN

Longitudinal study involving ECG and clinical follow up over (mean (SD)) 4.8 (1.8) and 6.2 (1.9) years, respectively, of patients stratified by CTG expansion size (E0 to E4).

PATIENTS

73 adult patients under annual review in a regional myotonic dystrophy clinic. Patients were grouped into E0/E1 (n = 25), E2 (n = 34), and E3/E4 (n = 14).

RESULTS

The proportion of patients with a QRS complex > 100 ms at baseline increased with the size of the CTG expansion (EO/E1, 4%; E2, 12%; E3/E4, 36%; p = 0.02). This trend was more pronounced at follow up (E0/E1, 4%; E2, 21%; E3/E4, 57%; p = 0.0004). The rate of widening of the QRS complex (ms/year) was similarly related to the size of the mutation (EO/E1, 0.4 (1.3); E2, 1.4 (2.5); E3/E4, 1.5 (1.6); p = 0.04). First degree atrioventricular block was present in 23% of patients at baseline and 34% at follow up, with no significant relation to expansion size. Seven patients suffered a cardiac event during follow up (sudden death in two, permanent pacemaker insertion in three, chronic atrial arrhythmia in two), of whom six were in CTG expansion group E2 or greater. Patients who experienced a cardiac event during follow up had more rapid rates of PR interval increase (9.9 (11.1) v 1.6 (2.9) ms/year; p = 0.008) and a trend to greater QRS complex widening (3.6 (4.5) v 0.9 (1.5) ms/year; p = 0.06) than those who did not.

CONCLUSIONS

Larger CTG expansions are associated with a higher rate of conduction disease progression and a trend to increased risk of cardiac events in myotonic dystrophy.

The right ventricular tachycardias

A variety of tachycardias originate from the right ventricle or use right ventricular structures as part of their circuit. They are characterized by a left bundle branch block pattern. Many of these tachycardias are relatively easy targets for radiofrequency catheter ablation. Ventricular tachycardia (VT) is the most common manifestation of arrhythmogenic right ventricular dysplasia, an often familial disease that can cause sudden death. Catheter ablation, antiarrhythmic drugs, or an implantable cardioverter-defibrillator may be used as therapy. Idiopathic right ventricular tachycardia has a benign course. It most often arises from the septal region of the right ventricular outflow tract. It commonly presents as nonsustained, repetitive monomorphic VT. The success rate of catheter ablation is greater than 90%. Bundle branch reentry occurs in patients with cardiomyopathy and His-Purkinje disease. It uses the right bundle branch anterogradely and the left bundle branch retrogradely. The QRS is very similar during VT and sinus rhythm. It can be cured by catheter ablation of the right bundle branch. VT seldom originates from the right ventricle in patients with coronary artery disease, idiopathic cardiomyopathy, or myocarditis. Atriofascicular (so-called Mahaim) fibers can sustain antidromic AV reentrant tachycardia. They represent an accessory AV node and His-Purkinje-like conduction system with atrial insertion in the right free wall near the tricuspid annulus and distal insertion directly into the right bundle branch. The accessory connection is ablated at the level of the tricuspid ring.

Therapeutic decision tree for patients with sustained ventricular tachyarrhythmias or aborted cardiac arrest: a critical review of the Antiarrhythmics Versus Implantable Defibrillator trial and the Canadian Implantable Defibrillator Study

Antiarrhythmic drugs, mainly amiodarone and sotalol, radiofrequency catheter ablation, and the implantable cardioverter defibrillator (ICD) are the 3 therapeutic options in patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Idiopathic VT, incessant VT, frequently recurring, hemodynamically stable VT, and VT based on bundle branch reentry, are candidates for radiofrequency catheter ablation. Patients with high-risk ventricular tachyarrhythmias should receive ICDs as initial therapy. Two studies, the Antiarrhythmics Versus Implantable Defibrillator trial (AVID) and the Canadian Implantable Defibrillator Study (CIDS) have tried to approach the problem of these high-risk ventricular tachyarrhythmias. Although at 3 years, the ICD in AVID demonstrated a significant relative risk reduction over amiodarone of 31.5%, CIDS could not duplicate this finding. At 3 years, the relative risk reduction conferred by the ICD over amiodarone in CIDS was only 13.7%. A careful analysis of both studies suggests that CIDS was insufficiently powered to demonstrate statistically significant benefits similar to those shown by AVID, and furthermore, seemed to include an undetermined number of low-risk VT patients. The problem in the CIDS trial in this regard was the recruitment of patients in whom the inclusion criteria were met by the arrhythmias induced during the electrophysiology stimulation study, but which did not exist in real life. In addition CIDS included 14% of patients with (1) undocumented syncope and inducible monomorphic sustained VT; or (2) long runs of spontaneous nonsustained VT. Under these circumstances, the therapeutic implications of AVID remain unchallenged.

Is it possible to identify infrahissian cardiac conduction abnormalities in myotonic dystrophy by non-invasive methods?

OBJECTIVE

To identify intracardiac conduction abnormalities in patients with myotonic dystrophy from their clinical, ECG, and genetic features.

METHODS

39 consecutive patients (mean (SD) age 42. 9 (12.1) years; 16 female, 23 male) underwent clinical examination, genetic studies, resting and 24 hour ambulatory ECG, signal averaged ECG, and electrophysiological studies.

RESULTS

23 patients suffered from cardiac symptoms, 23 had one or more cardiac conduction abnormality on resting ECG, one had sinus deficiency, and 21 (53.8%) had prolonged HV intervals. No correlation was found between the severity of the neurological symptoms, onset of disease, cardiac conduction abnormalities on ECG, and the intracardiac conduction abnormalities on electrophysiological study. The size of the DNA mutation was longer in the abnormal HV interval group than in the normal HV interval group (3.5 (1.8) v 2.2 (1.0) kb, p < 0.02). Signal averaged ECG parameters (total QRS duration (QRSD) and duration of low amplitude signals </= 40 microV (LAS 40)) were greater in patients with an abnormal HV interval than in those with a normal HV interval (123.4 (24.6) v 102.8 (12.3) ms and 47.5 (12.8) v 35.3 (8.8) ms, respectively; p < 0.005). Only the association of QRSD >/= 100 ms with LAS 40 >/= 36 ms identified patients with an abnormal HV interval with good sensitivity (80%) and specificity (83. 3%).

CONCLUSIONS

Infrahissian conduction abnormalities are common in myotonic dystrophy and can be identified using signal averaged electrocardiography.