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Show Table 1. Disorders associated with unexpected sudden cardiac death in the young. Disorder Common abbre- Inherited or _________________________________________viation_____________acquired_______ Potential symptoms prior to sudden death A. Associated with structural heart abnormalities at autopsy -the "cardiomyopathies" Hypertrophic cardiomyopathy HCM Dilated cardiomyopathy DCM Abnormal coronary artery None Marfan syndrome MFS Arrhythmogenic Right Ventricular cardie- ARVC (ARVD) myopathy (dysplasia) Myocarditis None Inherited Both Congenital but not inherited Inherited Inherited Acquired ¦ Chest pain, shortness of breath, palpitations, blackout spells Shortness of breath, fatigue, swelling Chest pain and/or shortness of breath Chest pain Palpitations, blackout spells Prior viral symptoms, fatigue B. No structural abnormalities found at autopsy - the "primary electrical system diseases" Long QT syndrome . LQTS Inherited QT prolonging medications Acquired LQTS Acquired Recreational drugs None Acquired Brugada syndrome BrS Inherited Progressive cardiac conduction system PCSD, Lev's or inherited disease* Lenegre's disease Catacholaminergic polymorphous ven- CPVT Inherited tricular tachycardia___________________________________________ Blackout spells Blackouts, palpitations Usually no prior symptoms Blackouts, palpitations Blackouts Blackouts, palpitations * PCSD may be cause structural changes which could be recognized at autopsy, but the area of abnormality is very small, and special techniques are required to recog-nize this, thus, structural abnormalities are often not identified on routine autopsy._________________________________________________________________ makers or implanted defibrillators, and counseling regarding physical activities and sports, and other behavioral modifications. An example of an expanded pedigree is shown in Figure 1. In addition to the "nuclear" family of parents and children, the pedigree should include grandparents, aunts and uncles, brothers and sisters, cousins, nephews and nieces, as possible. Screening of the members of this pedigree by a medical history and sometimes by medical testing is then performed to identify the affected members and determine the line of transmission of the gene mutation so that the appropriate side of the family can be evaluated. The first member of a family to be detected with a genetic disorder is called the proband. hi Figure 1 the proband is indicated by the arrow. Note that her parents and her children, as well as her brothers and sisters and their children are all included in the pedigree. After screening exams it is usually apparent who is affected with the disease, hi most instances it is possible to develop an even more expanded pedigree than the one shown here, particularly hi Utah where so many families have genealogy records and where extensive genealogy resources are available. When a child or young person dies suddenly and unexpectedly, an autopsy or postmortem examination is usually performed, hi about 50% of the cases the autopsy identifies a structural cardiac abnormality that explains the sudden death or cardiac arrest. When this condition is thought to be an inherited one, the other family members can be tested for that same structural defect, for example, hypertrophic cardiomyopathy. In the other 50% percent the autopsy is normal and no cause or explanation for the event is evident. Particularly in this group the family is left with many questions and fears. It is presumed that these cases were caused by a cardiac arrhythmia, and the family can then be evaluated for one of the primary electrical system diseases such as Long QT syndrome, usually by analysis of the electrocardiogram (ECG/EKG) of each family member. As demonstrated in Table 1, the symptoms of these disorders commonly include blackout spells, (the loss of consciousness; the medical term is syncope), heart palpitations manifested as perceived irregularities in the heartbeat, shortness of breath on exertion, and chest pain on exertion. Some of these symptoms are more suggestive of certain disorders than others. It is important to note that some of these symptoms, such as syncope, occur commonly in the normal population. A careful history of the circumstances and feelings experienced by the patient at the time of the syncope is required in order to detennine if the syncope is due to the common faint or due to one of these more dangerous disorders. The presence of similar symptoms in family members adds a strong suspicion that one is dealing with a familial disorder. Thus, the first screening of the family members is usually by the medical history and specifically the history for these types of symptoms. Additional screening might include a physical examination, an electrocardiogram, or an echocardiogram (an ultrasound study of the heart). Often these or other tests can clarify who has or does not have the condition. In some inherited diseases, genetic studies can be performed by obtaining the patient's DNA and analyzing it for gene mutations. The DNA can be obtained from a swab of the inner surface of the cheek (a buccal swab) or from blood, from which lymphocytes are extracted and DNA obtained from those cells, hi the last decade many, but not all, of the genes and mutations causing these inherited diseases have been identified. However, no routine or commercial genetic tests are available at present for any of these diseases, hi some circumstances it is possible to test family members by DNA analysis in research laboratories. Routine, commercial genetic testing will become available in the future, but only when all genes and mutations have been identified and improvements in technology and pricing have occurred. Long QT syndrome and Hypertrophic cardiomyopathy These are the two most common non-drug related causes of unexpected sudden death so some additional description of these disorders should be valuable. Hvpertrophic cardiomyopathy This genetic disease is commonly referred to as HCM, and is estimated to be present in 1:500 persons. HCM is inherited by autosomal dominant transmission, described above. It is thought to be the most common cause of sudden death in young athletes. HCM is the prototype of the genetic cardiomyopathies and much of what we know about the genetics of myocardial cell development and growth are derived from research on this condition. Many genes and mutations have been identified to cause HCM. The primary problem caused by these gene mutations is excessive thickening (hypertrophy) of the heart wall and there are many variants of the hypertrophy process dependent upon the specific gene. The hypertrophy can interfere with the proper functioning of the heart and it may become so thick that the normal blood flow to the heart is insufficient to meet the heart's Utah's Health: An Annual Review Volume DC 53 |
