Critical Evaluation of Current Hypotheses for the Pathogenesis of Hypertrophic Cardiomyopathy

Hereditary hypertrophic cardiomyopathy (HCM), due to mutations in sarcomere proteins, occurs in more than 1/500 individuals and is the leading cause of sudden cardiac death in young people. The clinical course exhibits appreciable variability. However, typically, heart morphology and function are normal at birth, with pathological remodeling developing over years to decades, leading to a phenotype characterized by asymmetric ventricular hypertrophy, scattered fibrosis and myofibrillar/cellular disarray with ultimate mechanical heart failure and/or severe arrhythmias. The identity of the primary mutation-induced changes in sarcomere function and how they trigger debilitating remodeling are poorly understood. Support for the importance of mutation-induced hypercontractility, e.g., increased calcium sensitivity and/or increased power output, has been strengthened in recent years. However, other ideas that mutation-induced hypocontractility or non-uniformities with contractile instabilities, instead, constitute primary triggers cannot yet be discarded. Here, we review evidence for and criticism against the mentioned hypotheses. In this process, we find support for previous ideas that inefficient energy usage and a blunted Frank–Starling mechanism have central roles in pathogenesis, although presumably representing effects secondary to the primary mutation-induced changes. While first trying to reconcile apparently diverging evidence for the different hypotheses in one unified model, we also identify key remaining questions and suggest how experimental systems that are built around isolated primarily expressed proteins could be useful.

Identifying Predictors of Longitudinal Decline in the Level of Medical Care Received by Adult Survivors of Childhood Cancer: A Report from the Childhood Cancer Survivor Study

OBJECTIVES

Characterize longitudinal changes in the use of medical care in adult survivors of childhood cancer.

DATA SOURCES

The Childhood Cancer Survivor Study, a retrospective cohort study of 5+ year survivors of childhood cancer.

STUDY DESIGN

Medical care was assessed at entry into the cohort (baseline) and at most recent questionnaire completion. Care at each time point was classified as no care, general care, or survivor-focused care.

DATA COLLECTION

There were 6,176 eligible survivors. Multivariable models evaluated risk factors for reporting survivor-focused care or general medical care at baseline and no care at follow-up; and survivor-focused care at baseline and general care at follow-up.

PRINCIPAL FINDINGS

Males (RR, 2.3; 95 percent CI 1.8-2.9), earning <$20,000/year (RR, 1.6; 95 percent CI 1.2-2.3) or ≤ high school education (RR, 2.5; 95 percent CI 1.6-3.8 and RR 2.0; 95 percent CI 1.5-2.7 for

CONCLUSIONS

While the incidence of late effects increases over time for survivors, the likelihood of receiving survivor-focused care decreases for vulnerable populations.

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Key Words

• Childhood cancer survivors
• delivery of health care
• health care access
• health insurance
• survivorship

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MESH Headings

• Adolescent
• Adult
• Age Factors
• Female
• Health Services/statistics & numerical data
• Health Status
• Humans
• Longitudinal Studies
• Male
• Middle Aged
• Neoplasms/epidemiology
• Neoplasms/therapy
• Retrospective Studies
• Sex Factors
• Socioeconomic Factors
• Survivors/statistics & numerical data
• Young Adult

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Grants

• U24 CA055727 NCI NIH HHS
• CA21765 NCI NIH HHS
• P30 CA008748 NCI NIH HHS
• P30 CA021765 NCI NIH HHS
• CA55727 NCI NIH HHS

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Affiliation(s) Collapse

Deformation patterns in genotyped patients with hypertrophic cardiomyopathy

AIMS

Echocardiographic strain imaging with two-dimensional speckle tracking is an emerging tool for defining cardiac function and identifying preclinical hypertrophic cardiomyopathy (HCM). In HCM, a reverse septal contour is a strong predictor of mutation positive sarcomeric HCM. The objective of this study was to determine whether left ventricular (LV) deformation patterns can differentiate between genotype positive and negative patients within a large HCM cohort.

METHODS AND RESULTS

One hundred and thirty one patients (89 males, age 55 ± 15 years) with clinically diagnosed HCM underwent comprehensive transthoracic echocardiography inclusive of LV strain imaging, LV dimensions and ejection fraction, septal contour and thickness, and identification of obstructive physiology. Longitudinal peak systolic strain was assessed from 17 LV myocardial segments blinded to the patient's genetic test results derived from comprehensive genotyping of nine myofilament HCM-associated genes. Genotyping revealed that 51 of 131 patients (39%) were mutation positive for sarcomeric/myofilament-HCM (genotype positive). Regional strain was lower in genotype-positive patients in mid inferoseptal (P = 0.004), basal anteroseptal (P = 0.04), and basal inferoseptal segments (P = 0.002) compared with HCM patients lacking a mutation (genotype negative). Strain patterns in reverse-curve, genotype-positive HCM differed significantly from genotype negative, sigmoidal HCM in multiple segments. However, when comparing genotype-negative and genotype-positive patients with the same septal morphology, there were no significant regional strain differences. Septal thickness positively correlated with global and basal anteroseptal longitudinal strain (r = 0.34 and r = 0.54, respectively, P < 0.0001).

CONCLUSION

Significant regional strain differences in genotyped HCM patients are dependent upon septal morphology or thickness, not genotype. Phenotypic expression of deformation patterns appears heterogeneous.

Assessment of strain and strain rate by two-dimensional speckle tracking in mice: comparison with tissue Doppler echocardiography and conductance catheter measurements

AIMS

This study was designed in order to compare the strain and strain rate deformation parameters assessed by speckle tracking imaging (STI) with those of tissue Doppler imaging (TDI) and conductance catheter measurements in chronic murine models of left ventricular (LV) dysfunction.

METHODS AND RESULTS

Twenty-four male C57BL/6J mice were assigned to wild-type (n = 8), myocardial infarction (n = 8) and transaortic constriction (n = 8) groups. Echocardiographic and conductance measurements were simultaneously performed at rest and during dobutamine infusion (5 µg/kg/min) in all animals 10 weeks post-surgery. The LV circumferential strain (Scirc) and the strain rate (SRcirc) were derived from grey scale and tissue Doppler data at frame rates of 224 and 375 Hz, respectively. Scirc and SRcirc by TDI/STI correlated well with the preload recruitable stroke work (PRSW) (r = -0.64 and -0.71 for TDI; r = -0.46 and -0.50 for STI, P < 0.05). Both modalities showed a good agreement with respect to Scirc and SRcirc (r = 0.60 and r = 0.63, P < 0.05). During stress, however, TDI-estimated Scirc and SRcirc values were predominantly higher than those measured by STI (P < 0.05). The similarity of Scirc and SRcirc measurements with respect to the STI/TDI data was examined by the Bland-Altman analysis.

CONCLUSION

In mice, the STI- and TDI-derived strain and strain rate deformation parameters relate closely to intrinsic myocardial function. At low heart rate-to-frame rate ratios (HR/FR), both STI and TDI are equally acceptable for assessing the LV function non-invasively in these animals. At HR/FR (e.g. dobutamine challenge), however, these methods cannot be used interchangeably as STI underestimates S and SR at high values.

The relative value of strain and strain rate for defining intrinsic myocardial function

It is well accepted that strain and strain rate deformation parameters are not only a measure of intrinsic myocardial contractility but are also influenced by changes in cardiac load and structure. To date, no information is available on the relative importance of these confounders. This study was designed to investigate how strain and strain rate, measured by Doppler echocardiography, relate to the individual factors that determine cardiac performance. Echocardiographic and conductance measurements were simultaneously performed in mice in which individual determinants of cardiac performance were mechanically and/or pharmacologically modulated. A multivariable analysis was performed with radial and circumferential strains and peak systolic radial and circumferential strain rates as dependent parameters and preload recruitable stroke work (PRSW), arterial elastance ( Ea), end-diastolic pressure, and left ventricular myocardial volume (LVMV) as independent factors representing myocardial contractility, afterload, preload, and myocardial volume, respectively. Radial strain was most influenced by Ea (β = −0.58, R2 = 0.34), whereas circumferential strain was strongly associated with Ea and moderately with LVMV (β = 0.79 and −0.52, respectively, R2 = 0.54). Radial strain rate was related to both PRSW and LVMV ( β = 0.79 and −0.62, respectively, R2 = 0.50), whereas circumferential strain rate showed a prominent correlation only with PRSW (β = −0.61, R2 = 0.51). In conclusion, strain (both radial and circumferential) is not a good surrogate measure of intrinsic myocardial contractility unless the strong confounding influence of afterload is considered. Strain rate is a more robust measure of contractility that is less influenced by changes in cardiac load and structure. Thus, peak systolic strain rate is the more relevant parameter to assess myocardial contractile function noninvasively.

Early changes in left ventricular long-axis function in Friedreich ataxia: relation with the FXN gene mutation and cardiac structural change

OBJECTIVE

Friedreich ataxia (FRDA) is an autosomal recessive condition due to a GAA triplet expansion in the FXN gene that causes increased left ventricular (LV) wall thickness and can progress to LV systolic dysfunction. However, the changes in myocardial function that occur before a reduction in LV ejection fraction are incompletely understood.

METHODS

LV long-axis function was assessed by measurement of tissue Doppler imaging (TDI) peak systolic (S`), early diastolic (E`), and atrial velocities (A`) at the septal and lateral borders of the mitral annulus in 60 subjects homozygous for a GAA expansion in the FXN gene who had preserved LV ejection fraction. Comparison was made with 60 sex- and age-matched controls. TDI velocities at 5 years were compared with baseline values in 17 FRDA subjects with follow-up studies who still had preserved ejection fraction.

RESULTS

S` and E` were reduced in FRDA subjects at both the septal and the lateral mitral annular borders. Lateral E` was independently and inversely related to age, blood pressure, septal wall thickness, and the number of GAA repeats in the smaller allele of the FXN gene, whereas septal E` was not correlated with GAA repeat number. At 5 years, there was a reduction in lateral S` and E` but no change in septal TDI velocities.

CONCLUSION

Subjects with FRDA have impairment of septal and lateral long-axis LV function, but there also seem to be regional differences in the effects of this condition that are at least partly related to the degree of genetic abnormality.

Advances in echocardiography

PURPOSE OF REVIEW

This study will outline recent advances in echocardiography and their impact in the understanding of cardiac morphology and ventricular function.

RECENT FINDINGS

Evaluation of morphologic abnormalities in pediatric cardiology has benefited greatly from three-dimensional echocardiography, particularly with the introduction of high-frequency transducers. The size of cardiovascular structures is frequently affected by heart disease, and a systematic approach to adjust measurements for the effects of body size and age has helped to distinguish a normal structure from an abnormal one. Quantification of diastolic and systolic function continues to be a major focus in echocardiography. New modalities such as tissue Doppler imaging and speckle tracking echocardiography have provided new parameters to assess myocardial performance, and these parameters include myocardial velocities, ventricular twist and torsion, strain and strain rate, and mechanical dyssynchrony. Mechanical dyssynchrony analysis has been particularly useful in cardiac resynchronization therapy, a novel treatment for heart failure which shows great promise.

SUMMARY

Improved delineation of cardiac morphology has greatly augmented the current understanding of congenital heart diseases, and management strategies have been modified based on three-dimensional echocardiographic findings. The introduction of new parameters to evaluate ventricular function has provided early markers for cardiovascular impairment in several disease states, thereby allowing clinicians to monitor these patients more closely.

The gold standard for noninvasive imaging in congenital heart disease: echocardiography

PURPOSE OF REVIEW

Echocardiography in pediatric and congenital heart disease is a key diagnostic technique in patients with congenital heart disease. Due to new technological developments, it has become a rapidly evolving field.

RECENT FINDINGS

In this review, we focus on recent developments in standardization and validation of standard techniques in pediatric and congenital echocardiography. This is mainly related to standardization of image acquisition and normalization of measurements for body size. The rest of the review is focused on the application of three-dimensional echocardiography, tissue Doppler imaging and Speqle tracking techniques to pediatric heart disease.

SUMMARY

New developments in standardization of echocardiography, the introduction of three-dimensional echocardiography and new functional techniques such as tissue Doppler and Speqle tracking strengthen the position of pediatric echocardiography as the most important diagnostic tool for patients with congenital heart disease.