Case 2 -

Arrhythmic Sudden Cardiac Death with Normal Heart Gaetano Thiene

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Clinical history Tonsillectomy at the age of 3, surgical repair of left inguinal hernia at the age of 9. He has been performing regular sport activity (karate) since the age of 8. No family history of cardiac diseases or juvenile sudden death At the age of 12, first syncopal episode on emotion (watching television): cardiological check-up (physical examination and 12 lead ECG) were normal (fig.1). Basal 12 lead ECG performed at the time of first syncopal episode (12 years): sinus rhythm (69 bpm), normal PQ and QT intervals and ST segment At the age of 16, while he was watching a football game on television(10:30 PM), he exulted at the goal and soon after he had sudden loss of consciousness. Prompt cardiopulmonary resuscitation (CPR) manoeuvers were unsuccessful and death was ascertained 1 hour later (11:30 PM). Autopsy ruled out unnatural (negative toxicologic investigation) and extracardiac causes of death. Gross examination of the heart revealed heart weight 380 gr, transverse diameter 9,5 cm, longitudinal diameter 9,5 cm. LV wall thickness 13 mm, septal thickness 14 mm, RV free wall 3 mm (fig. 2). Gross examination of the heart: transverse section of the heart at the apical third showing a normal myocardium. Origin and course of coronary arteries were normal, patent. Semilunar and atrioventricular valves were structurally normal, except for mild myxoid degeration of mitral valve leaflets (Fig.3). There was no evidence of myocardial hypertrophy, cavity enlargement, fatty infiltration and right and/or left ventricular aneurysm formation (grossly normal heart). Gross examination of the heart, view of the left atrial cavity from above. Note the normal mitral valve leaflets with mild myxoid degeneration (b, close-up of a) Multiple samples of the myocardium are taken for histology as well as for molecular pathology investigation, including spleen and blood (frozen -80°). At histology, diffuse interstitial oedema with scarce interstitial inflammatory cells, in the absence of myocyte damage, was evident (fig.4). No replacement-type fibrosis, fatty infiltration, small vessel disease, myocardial disarray were detected. Histology of the ventricular myocardium. a, b,c ) mild interstitial edema in the absence of myocyte necrosis; d) immunohistochemistry investigation reveals focal T lymphocytes (CD45RO positive) Case 2 - Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer Case 2 - Figure 1 Basal 12 lead ECG performed at the time of first syncopal episode (12 years): sinus rhythm (69 bpm), normal PQ and QT intervals and ST segment Case 2 - Figure 2 Gross examination of the heart: transverse section of the heart at the apical third showing a normal myocardium. Case 2 - Figure 3 Gross examination of the heart, view of the left atrial cavity from above. Note the normal mitral valve leaflets with mild myxoid degeneration (b, close-up of a) Case 2 - Figure 4A & B Histology of the ventricular myocardium. a, b ) mild interstitial edema in the absence of myocyte necrosis Case 2 - Figure 4 C & D Histology of the ventricular myocardium. c ) mild interstitial edema in the absence of myocyte necrosis; d) immunohistochemistry investigation reveals focal T lymphocytes (CD45RO positive) Autopsy diagnosis Arrhythmic Sudden Cardiac Death with Normal Heart. Family screening and molecular diagnosis Based upon the decedent's clinical history, showing at age of 12 and 16 two unexplained episodes of syncope on emotion, a ion channel disease was suspected. Long QT syndrome was excluded on the basis of a previous normal basal 12 ECG, so the hypothesis of catecholaminergic polymorphic ventricular tachycardia (CPVT) due to ryanodine receptor 2 (Ryr2) gene mutation was advanced. Mutation screening was performed on 35 amplicons corresponding to 29 critical exons. DNA sequencing of abnormal DHPLC profiles confirmed the presence of a single nucleotide substitutions A2387P. This missense mutation occurred in evolutionarily conserved regions of the protein in FKBP12.6 interacting domains, which is believed to cause increased RyR2 activity after PKA phosphorylation (gain of function). All family members underwent 12-lead ECG, Holter ECG, signal-averaged ECG, 2-dimensional and Doppler echocardiogram, and exercise stress test. The same missense mutation was found also in his mother. She had the exercise stress test interrupted at 100 Watt due to the onset of effort-induced polymorphic ventricular arrhythmias, whereas at rest she did not show any arrhythmia. The brother and the father were not affected. The mother was put on beta-blocker therapy with acebutolol. Discussion. Inherited cardiac disorders at risk of sudden cardiac death (SCD) can be subdivided into structural (arrhythmogenic right ventricular cardiomyopathy, hypertrophic cardiomyopathy, Lenegre disease-progressive cardiac conduction defect) and non structural (Brugada syndrome, Long QT and Short QT syndromes and CPVT [1]. In the former group, the autopsy with gross and histologic examination is enough to reach the final diagnosis of the cause of SCD. However, tissue sampling and preservation for molecular study purposes is also advisable for subsequent genotype-phenotype correlations. On the opposite, the non-structural genetically determined heart diseases at risk of SCD could take advantage from molecular pathology investigation, since molecular genetics is the only way to provide a final diagnosis, being autopsy completely negative ("mors sine materia"). In the case herein reported, long QT, short QT and Brugada syndromes were excluded on the basis of a previous normal basal 12 ECG, so CPVT due to ryanodine receptor 2 gene mutation was postulated. This arrhythmias was first described by Coumel et al. in 1978 [2, 3] as a distinct clinical entity of unknown origin with manifestation in childhood and adolescence. The hallmark of this disease was the polymorphic ventricular tachycardia that occurred during effort or emotion and was reproducible during stress test. Basal ECG is normal. More recently, CPVT has been recognized as a genetically determined arrhythmogenic disease and its pathophysiological mechanisms are being progressively unveiled. Syncope, triggered by exercise or acute emotion, is often the first manifestation even is SCD may occur in previously asymptomatic subject. In approximately 30% of cases, the family history reveals one or multiple premature SCD, which usually occur during childhood, even though later onset (after age 20) events have been reported. These SCD occurring in individuals without cardiac structural abnormalities may lead to the postmortem diagnosis of idiopathic ventricular fibrillation. The autosomal dominant CPVT was mapped in 1999 to chromosome 1q42-43 [4] and the first genetic defects in CPVT patients with structural normal heart were reported in 2001 by Priori et al [5], w ho demonstrated mutation of the human RyR2 in four families. Noteworthy, our group described Ryr2 mutations in the ARVD2 variant of ARVC/D, but we must recognize that right ventricular abnormalities are very segmental, mostly confined to the apex, and different from those commonly reported in typical ARVC/D [6]. The RyR2 receptor is involved in the calcium release from the sarcoplasmic reticulum. Mutations of this gene cause malfunction of the receptor resulting in intracellular calcium overload. Ventricular arrhythmias are usually induced during exercise testing or emotion, and the heart rate threshold at which they appear is different in each subject. Bauce et al [7] studied eight families with RyR2 mutations . Noteworthy, the basal twelve-lead ECG was normal in all Ryr2 mutation carriers and only 65% of them presented with effort-induced arrhythmic symptoms or signs. This emphasizes the role of genetic screening to achieve a diagnosis. When diagnosed, patients are strongly advised to avoid strenuous physical activity. During a mean follow-up of 6.5 years, no patient on antiarrhythmic therapy had syncope or died suddenly Tester et al. [8] in an autopsy cohort of 49 cases of unexplained SCD, found evidence of a RyR2 mutation in 14% of cases. This study represents the first molecular autopsy of RyR2 in medical examiner-referred cases of unexplained SCD and suggest that postmortem genetic testing of RyR2 should be considered as a part of the comprehensive forensic autopsy investigation of a unexplained SCD [9, 10]. References Thiene G, Corrado D, Basso C. Cardiomyopathies: is it time for a molecular classification? Eur Heart J 2004; 25:1772-5 Coumel P, Fidelle J, Lucet V, Attuel P, Bouvrain Y. Catecholamine-induced severe ventricular arrhythmias with Adams-Stokes syndrome in children: report of four cases. Br Heart J 1978;40:28-37 Leenhardt A, Lucet V, Denjoy I, Grau F, Ngoc DD, Coumel P. Catecholaminergic polymorphic ventricular tachycardia in children. A 7-year follow-up of 21 patients . Circulation. 1995; 91:1512-9 Swan H, Piippo K, Viitasalo M, Heikkila P, Paavonen T, Kainulainen K, Kere J, Keto P, Kontula K, Toivonen L. Arrhythmic disorder mapped to chromosome 1q42-q43 causes malignant polymorphic ventricular tachycardia in structurally normal hearts . J Am Coll Cardiol 1999; 34:2035-42 Priori SG, Napolitano C, Tiso N, Memmi M, Vignati G, Bloise R, Sorrentino V, Danieli GA. Mutations in the cardiac ryanodine receptor gene (hRyR2) underlie catecholaminergic polymorphic ventricular tachycardia . Circulation. 2001; 103:196-200 Tiso N, Stephan DA, Nava A, et al. Identification of mutations in the cardiac ryanodine receptor gene in families affected with arrhythmogenic right ventricular cardiomyopathy type 2 (ARVD2). Hum Mol Genet 2001; 10:189-194 Bauce B, Rampazzo A, Basso C, Bagattin A, Daliento L, Tiso N, Turrini P, Thiene G, Danieli GA, Nava A. Screening for ryanodine receptor type 2 mutations in families with effort-induced polymorphic ventricular arrhythmias and sudden death. J Am Coll Cardiol 2002; 40:341-9 Tester DJ, Spoon DB, Valdivia HH, Makielski JC, Ackerman MJ. Targeted mutational analysis of the RyR2-encoded cardiac ryanodine receptor in sudden unexplained death: a molecular autopsy of 49 medical examiner/coroner's cases. Mayo Clin Proc. 2004; 79:1380-4. Basso C, Burke M, Fornes P, Gallagher PJ, de Gouveia RH, Sheppard M, Thiene G, van der Wal A; on behalf of the Association for European Cardiovascular Pathology. Guidelines for autopsy investigation of sudden cardiac death. Virchows Arch. 2008;452:11-8. Carturan E, Tester DJ, Brost BB, Basso C, Thiene G, Ackerman MJ. Postmortem Genetic Testing for Conventional Autopsy Negative Sudden Unexplained Death: An Evaluation of Different DNA Extraction Protocols and the Feasibility of Mutational Analysis from Archival Paraffin Embedded Heart Tissue. Am J Clin Pathol 2008 (in press)