Death is most often sudden in HCM and unfortunately this may occur in asymptomatic patients, in those who were unaware that they have the disease, or in individuals with an otherwise stable course.
The mechanisms that result in sudden death remain unresolved. The identification of patients at high risk of sudden death presents great difficulties for the average and expert clinicians.
A. Genotyping
Genotyping is not available as a routine clinical test, and most important, it is currently problematic in prognostic assessment. The findings of Ackerman et al. of only 1% malignant mutation in 293 patients is important and is in keeping with several other observations. Even within so-called high-risk families there is a variable disease expression and prognosis. Watkins et al. described a large Scottish family with mutation in TNNT2 in which 8 died suddenly before age 30, but 8 others lived to be 70–80 years old. Several other reports of this type have been noted.
B. Clinical Evaluation
Because the promise held for genotyping is not likely to materialize, assessment of risk is based mainly on clinical evaluation and specific investigations. Clinical parameters that may assist in the assessment of risk for sudden death, however, remain unsystematic and haphazard. Mckenna et al. made the point that at best, clinical risk markers are only modestly predictive of short-to-medium term risk of sudden death. The presence of a severe outflow tract gradient does not correlate with the risk of sudden death.

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