Vascular mechanisms of sudden death in hypertrophic cardiomyopathy, including blood pressure responses to exercise

Hypotension in hereditary cardiomyopathy

It is well accepted that hypertension may lead to the development of heart failure (HF). However, little is known about the development of hypotension that may contribute to the onset of hereditary cardiomyopathy (HCM), thus promoting heart failure and early death. The purpose of this study is to verify whether a decrease in blood pressure takes place during different phases of HCM (asymptomatic, necrosis, hypertrophy, and heart failure). Using the well-known animal model, the UM-X7.1 hamster strain of HCM (HCMH), our results showed the absence of a change in mean arterial pressure (MAP) during the asymptomatic phase preceding the development of necrosis in HCMHs when compared to age-matched normal hamster (NH). However, there was a progressive decrease in MAP that reached its lowest level during the heart failure phase. The MAP during the development of the necrosis phase of HCM was accompanied by a significant increase in the level of the sodium-hydrogen exchanger, NHE1. Treatments with the potent NHE1 inhibitor, EMD 87580 (rimeporide), did not affect MAP of NH. However, treatments with EMD 87580 during the three phases of the development of HCM significantly reversed the hypotension associated with HCM.Our results showed that the development of HCM is associated with hypotension. These results suggest that a decrease in blood pressure could be a biomarker signal for HCM leading to HF and early death. Since the blockade of NHE1 significantly but partially prevented the reduction in MAP, this suggests that other mechanisms can contribute to the development of hypotension in HCM.

Sudden Cardiac Death in the Young

Although the occurrence of sudden cardiac death (SCD) in a young person is a rare event, it is traumatic and often widely publicized. In recent years, SCD in this population has been increasingly seen as a public health and safety issue. This review presents current knowledge relevant to the epidemiology of SCD and to strategies for prevention, resuscitation, and identification of those at greatest risk. Areas of active research and controversy include the development of best practices in screening, risk stratification approaches and postmortem evaluation, and identification of modifiable barriers to providing better outcomes after resuscitation of young SCD patients. Institution of a national registry of SCD in the young will provide data that will help to answer these questions.

Orthostatic blood pressure test for risk stratification in patients with hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common cause of sudden cardiac death (SCD) in young adults, mainly ascribed to ventricular tachycardia (VT). Assuming that VT is the major cause of (pre-) syncope in HCM patients, its occurrence is essential for SCD risk stratification and primarily preventive ICD-implantation. However, evidence of VT during syncope is often missing. As the differentiation of potential lethal causes for syncope such as VT from more harmless reasons is crucial, HCM patients were screened for orthostatic dysregulation by using a simple orthostatic blood pressure test.

METHODS

Over 15 months (IQR [9;20]) 100 HCM patients (55.8±16.2 yrs, 61% male) were evaluated for (pre-)syncope and VT (24h-ECGs, device-memories) within the last five years. Eighty patients underwent an orthostatic blood pressure test. Logistic regression models were used for statistical analysis.

RESULTS

In older patients (>40 yrs) a positive orthostatic test result increased the chance of (pre-) syncope by a factor of 63 (95%-CI [8.8; 447.9], p<0.001; 93% sensitivity, 95%-CI [76; 99]; 74% specificity, 95%-CI [58; 86]). No correlation with VT was shown. A prolonged QTc interval also increased the chance of (pre-) syncope by a factor of 6.6 (95%-CI [2.0; 21.7]; p=0.002).

CONCLUSIONS

The orthostatic blood pressure test is highly valuable for evaluation of syncope and presyncope especially in older HCM patients, suggesting that orthostatic syncope might be more relevant than previously assumed. Considering the high complication rates due to ICD therapies, this test may provide useful information for the evaluation of syncope in individual risk stratification and may help to prevent unnecessary device implantations, especially in older HCM patients.

Genetics of sudden cardiac death in children and young athletes

Sudden cardiac death is a rare but socially devastating event. The most common causes of sudden cardiac death are congenital electrical disorders and structural heart diseases. The majority of these diseases have an incomplete penetrance and variable expression; therefore, patients may be unaware of their illness. In several cases, physical activity can be the trigger for sudden cardiac death as first symptom. Our purpose is to review the causes of sudden cardiac death in sportive children and young adults and its genetic background. Symptomatic individuals often receive an implantable cardioverter-defibrillator, the preventive treatment for sudden cardiac death in most of cases due to channelopathies, which can become a challenging option in young and active patients. The identification of one of these diseases in asymptomatic patients has similarly a great impact on their everyday life, especially on their ability to undertake competitive physical activities, and the requirement of prophylactic treatment. We review main causes of sudden cardiac death in relation to its genetics and diagnostic work-up

Long-term follow-up of children and adolescents diagnosed with hypertrophic cardiomyopathy: risk factors for adverse arrhythmic events

Our aim was to identify prognostic factors for an arrhythmic event (AE) in children with hypertrophic cardiomyopathy (HCM) without a previous AE. One hundred thirty-one nonconsecutive patients (≤ 20 years) with HCM but no previous AE were evaluated at the NIH Clinical Center from 1980 to 2001. At a median follow-up of 6.4 years, 22 patients experienced an AE [sudden death (SD) (n = 12), resuscitated cardiac arrest (n = 3), clinical sustained ventricular tachycardia (VT) (n = 2), and implantable cardiac defibrillator discharge (n = 5)], resulting in a 2% annual AE rate. Baseline factors that were most predictive in univariate risk analysis included ventricular septal thickness (ST) (P = 0.01), VT induction by programmed ventricular stimulation (PVS) (P = 0.01), age (P = 0.05), and presyncope/syncope (P = 0.05). In multivariate analysis, ST, age, presyncope/syncope, and PVS were not independently predictive of risk for an AE. However, the 5-year event rates for AE was 15% (95% CI: 5-23%) if ST ≥ 20 mm, 19% (95% CI: 6-31%) when age ≥ 13 years and ST ≥ 20 mm were combined together, and 23% (95% CI: 3-39%) when PVS and ST ≥ 20 mm were combined together. Of the various risk factors that were considered in our pediatric HCM cohort, ST and inducible VT were the most significant univariate predictors of risk for an AE. More traditional risk factors identified in older patients (family history of SD, VT on Holter, and exercise-induced hypotension) were not predictive of an AE in patients age under 21 years.

Hypertrophic cardiomyopathy as a cause of sudden death

Hypertrophic cardiomyopathy (HCM) is the main cause of sudden unexpected death in the young and especially in young athletes with an incidence up to 2.3 per 100,000 athletes and year. Risk stratification models including patient history (syncope, familial risk of sudden death) and findings in noninvasive tests (nonsustained ventricular tachycardia, abnormal blood pressure response during exercise, maximum left ventricular wall thickness > or = 30 mm) have been developed in order to estimate the risk of individual patients. Echocardiographic parameters are helpful in distinguishing HCM from athlete's heart. Definitive diagnosis of HCM implicates disqualification from competitive sports resulting in a significant reduction of sudden cardiac death due to HCM during sports competition. This positive development should lead to a widespread preparticipation screening of athletes including historical, clinical, and electrocardiographic examination. At least in borderline findings and symptomatic athletes, an additional echocardiogram should be performed in order to minimize or better exclude the risk of sudden cardiac death.

Abnormal blood pressure response to exercise occurs more frequently in hypertrophic cardiomyopathy patients with the R92W troponin T mutation than in those with myosin mutations

Abnormal blood pressure response to exercise is reported to occur in up to a third of hypertrophic cardiomyopathy (HCM) cases and is associated with an increased risk of death, particularly in the young, but it is not known whether the HCM-causing mutation influences blood pressure response to exercise. The purpose of this article is to ascertain whether the blood pressure response to exercise differs among carriers of the R92W mutation in the cardiac troponin T gene (TNNT2), which has been associated with an increased risk of sudden cardiac death in young males; carriers of mutations in the cardiac β-myosin heavy chain gene (MYH7); and their noncarrier relatives. Thirty R92W_TNNT2 carriers, 51 MYH7 mutation carriers, and 68 of their noncarrier relatives were subjected to bicycle ergonometric exercise testing to assess blood pressure response to, as well as heart rate recovery after, exercise. Additional echocardiographic and demographic details were documented for all participants. R92W_TNNT2 carriers demonstrated significantly more abnormal blood pressure responses to exercise (P = .021; odds ratio 3.03; confidence interval 1.13–8.12) and smaller increases in systolic blood pressure than MYH7 mutation carriers or related noncarrier control individuals. Although abnormal blood pressure response occurred at similar frequencies in males in all groups (23%–26%), the percentage of R92W_TNNT2 females with abnormal blood pressure response was 64%, compared with 25% for MYH7 and 22% for noncarriers. Therefore, these results show that blood pressure response to exercise is influenced by genotype and gender in patients with HCM.

The value of changes in QRS width and in ST-T segment during exercise test in hypertrophic cardiomyopathy for identification of associated coronary artery disease

OBJECTIVES

Non-invasive methods cannot reliably predict the presence of coronary artery disease (CAD) in hypertrophic cardiomyopathy (HCM). This study aims to define the accuracy of QRS width changes versus standard ST-T criteria for recognition of associated ischemic CAD in patients with HCM undergoing exercise testing (ET).

METHODS

A retrospective study including patients with HCM. HCM was defined by left ventricular hypertrophy (LVH) of unknown etiology of at least 15 mm. Coronary angiography was performed as a gold standard for definition of CAD (> or =70% obstruction in at least one major artery). QRS width duration was measured at peak ET by a computerized method employing an optical scanner. No changes in QRS width or shortening during ET were considered normal; QRS width prolongation of more than 3 ms was defined as abnormal.

RESULTS

68 patients (56/12 M/F) aged 60+/-12 y were studied. During ET, abnormal QRS response was found in 40 (58.8%) and Ischemic ST-T changes in 52 (76.5%) patients. CAD in at least one artery was diagnosed in 31 patients (45.5%). The sensitivity of QRS width versus ST-T changes during ET for associated CAD was 82% and 28%, respectively. Specificity was 75% and 48%, respectively. Positive and negative predictive values were 88%; 68% for QRS width and 67%; 59% for ST-T changes respectively.

CONCLUSIONS

In patients with HCM undergoing ET, the association with CAD was more accurately predicted by an increase in QRS complex width than by standard criteria of ST-T segment changes. Thus, its use should be encouraged, especially in patients with HCM.

Heart rate variability and ambulatory blood pressure monitoring in young patients with hypertrophic cardiomyopathy

BACKGROUND

Sudden cardiac death commonly occurs in young patients with hypertrophic cardiomyopathy (HCM); however, their heart rate variability (HRV) and blood pressure (BP) response to daily life activities is not well known.

METHODS AND RESULTS

HRV and ambulatory BP monitoring were performed in 20 patients (age range: 7-21 years) and 57 age-matched healthy volunteers (age range: 10-22 years). Time domain variables and spectral data were obtained at hourly intervals throughout the day. To determine the BP response to daily life activities, the ratios of the mean BP and pulse pressure in the morning, afternoon, and night to those during sleeping were calculated. The association between the BP level and HRV was also evaluated. The HCM patients showed significantly increased sympathovagal imbalance and decreased parasympathetic activity in the early morning, around noon, and in the early evening. This abnormality was independent of cardiac symptoms. Symptomatic patients showed a significantly lower systolic BP response in the morning, and a higher incidence of dissociation between sympathetic activity and BP response than asymptomatic patients.

CONCLUSION

An abnormal BP response in the presence of impaired HRV appears to be predictive for cardiac events in young patients with HCM.