Regional left ventricular myocardial contraction abnormalities and asynchrony in patients with hypertrophic cardiomyopathy evaluated by magnetic resonance spatial modulation of magnetization myocardial tagging

Characterization of motion patterns by a spatio-temporal saliency descriptor in cardiac cine MRI

BACKGROUND AND OBJECTIVE

Abnormalities of the heart motion reveal the presence of a disease. However, a quantitative interpretation of the motion is still a challenge due to the complex dynamics of the heart. This work proposes a quantitative characterization of regional cardiac motion patterns in cine magnetic resonance imaging (MRI) by a novel spatio-temporal saliency descriptor.

METHOD

The strategy starts by dividing the cardiac sequence into a progression of scales which are in due turn mapped to a feature space of regional orientation changes, mimicking the multi-resolution decomposition of oriented primitive changes of visual systems. These changes are estimated as the difference between a particular time and the rest of the sequence. This decomposition is then temporarily and regionally integrated for a particular orientation and then for the set of different orientations. A final spatio-temporal 4D saliency map is obtained as the summation of the previously integrated information for the available scales. The saliency dispersion of this map was computed in standard cardiac locations as a measure of the regional motion pattern and was applied to discriminate control and hypertrophic cardiomyopathy (HCM) subjects during the diastolic phase.

RESULTS

Salient motion patterns were estimated from an experimental set, which consisted of 3D sequences acquired by MRI from 108 subjects (33 control, 35 HCM, 20 dilated cardiomyopathy (DCM), and 20 myocardial infarction (MINF) from heterogeneous datasets). HCM and control subjects were classified by an SVM that learned the salient motion patterns estimated from the presented strategy, by achieving a 94% AUC. In addition, statistical differences (test t-student, p<0.05) were found among groups of disease in the septal and anterior ventricular segments at both the ED and ES, with salient motion characteristics aligned with existing knowledge on the diseases.

CONCLUSIONS

Regional wall motion abnormality in the apical, anterior, basal, and inferior segments was associated with the saliency dispersion in HCM, DCM, and MINF compared to healthy controls during the systolic and diastolic phases. This saliency analysis may be used to detect subtle changes in heart function.

Hypertrophic Cardiomyopathy from A to Z: Genetics, Pathophysiology, Imaging, and Management

Hypertrophic cardiomyopathy (HCM) is a heterogeneous group of diseases related to sarcomere gene mutations exhibiting heterogeneous phenotypes with an autosomal dominant mendelian pattern of inheritance. The disorder is characterized by diverse phenotypic expressions and variable natural progression, which may range from dyspnea and/or syncope to sudden cardiac death. It is found across all racial groups and is associated with left ventricular hypertrophy in the absence of another systemic or cardiac disease. The management of HCM is based on a thorough understanding of the underlying morphology, pathophysiology, and clinical course. Imaging findings of HCM mirror the variable expressivity and penetrance heterogeneity, with the added advantage of diagnosis even in cases where a specific mutation may not yet be found. The diagnostic information obtained from imaging varies depending on the specific stage of HCM-phenotype manifestation, including the prehypertrophic, hypertrophic, and later stages of adverse remodeling into the burned-out phase of overt heart failure. However, subtle or obvious, these imaging findings become critical components in diagnosis, management, and follow-up of HCM patients. Although diagnosis of HCM traditionally relies on clinical assessment and transthoracic echocardiography, recent studies have demonstrated increased utility of multidetector computed tomography (CT) and particularly cardiac magnetic resonance (MR) imaging in diagnosis, phenotype differentiation, therapeutic planning, and prognostication. In this article, we provide an overview of the genetics, pathophysiology, and clinical manifestations of HCM, with the spectrum of imaging findings at MR imaging and CT and their contribution in diagnosis, risk stratification, and therapy.

Characterization and quantification of curvature using independent coordinates method in the human left ventricle by magnetic resonance imaging to identify the morphology subtype of hypertrophy cardiomyopathy

The patterns of ventricular hypertrophy are critical determinants of blood flow and function, but are variable. Therefore, it is clinically relevant to assess the hypertrophic shape patterns to better characterize and identify the morphological subtypes. We proposed and developed an independent coordinates method (ICM) to quantify the regional shape of the left ventricle in terms of curvature. 19 normal subjects and 5 HCM (hypertrophic cardiomyopathy) patients with different morphological subtype (i.e., septal hypertrophy, mid-ventricular hypertrophy, reverse curvature septum hypertrophy and sigmoid septum hypertrophy) were recruited and underwent magnetic resonance scans. The curvature along the endocardial and epicardial surface was computed using ICM method and was compared in HCM patients against normal subjects. The results showed that curvature plots are variable in different morphological subtype. The curvature pattern demonstrated the utilities in delineating different subtype. In conclusion, ICM method to quantify regional curvature of the left ventricle from magnetic resonance imaging are feasible in normal subjects and those with hypertrophy cardiomyopathy, which may serve as a novel approach to depict local shape of the left ventricle and to assess the morphological subtype in clinical practice.

Ventricular mechanics: techniques and applications

Magnetic resonance assessment of regional myocardial function is a novel potentially important tool for early identification of cardiac pathology. Many cardiac magnetic resonance techniques have been developed for detection and quantification of regional strain abnormalities including steady-state free-precession CINE, tagging, displacement encoding with stimulated echoes, strain encoding imaging, and feature tracking. Potential clinical applications of magnetic resonance strain imaging include early detection of systolic dysfunction in heart failure patients with both ischemic and nonischemic etiologies.

Advances of cardiovascular MRI in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic disease characterized by abnormal myocardial hypertrophy, which can lead to a wide clinical spectrum, including sudden cardiac death and heart failure. Cardiac MRI has a significant role in establishing the diagnosis of HCM. In the three principal management issues related to HCM; testing of family members of affected individuals; assessing the risk of sudden cardiac death from lethal ventricular arrhythmias; and selection of appropriate treatments for left ventricular outflow obstruction, cardiac MRI has established or emerging roles.

Measuring Left Ventricular Volumes in Two-Dimensional Echocardiography Image Sequence Using Level-set Method for Automatic Detection of End-Diastole and End-systole Frames

BACKGROUND

Identifying End-Diastole (ED) and End-Systole (ES) frames is highly important in the process of evaluating cardiac function and measuring global parameters accurately, such as Ejection Fraction (EF), Cardiac Output (CO) and Stroke Volume.

OBJECTIVES

The current study aimed to develop a new method based on measuring volume changes in Left Ventricle (LV) during cardiac cycle.

MATERIAL AND METHODS

For this purpose, the Level Set method was used both in detecting endocardium border and quantifying cardiac function of all frames.

RESULTS

Demonstrating LV volumes displays ED and ES frames and the volumes used in calculating the required parameters.

CONCLUSIONS

Since ES and ED frames exist in iso-volumic phases of the cardiac cycle with minimum and maximum values of LV volume signals, such peaks can be utilized in finding related frames.

The Association of Left Ventricular Hypertrophy with Intraventricular Dyssynchrony at Rest and during Exercise in Hypertensive Patients

Background

Impaired exercise tolerance with dyspnea is common in hypertensive patients and this may be due to the exaggeration of nonuniform ventricular activation during exercise. So we want to evaluate the effect of left ventricular hypertrophy (LVH) on systolic intraventricular dyssynchrony during exercise.

Methods

A total of 85 patients with hypertension who having exertional dyspnea and 30 control individuals were enrolled. Exercise stress echocardiography was performed using a symptom limited, multistage supine bicycle test. To evaluate the dyssynchrony of left ventricular (LV), we calculated the standard deviation (SD) of the averaged time-to-peak systolic velocity (TPs-SD, ms) of 12 middle and basal LV segments obtained from the three standard apical views at rest and peak exercise.

Results

There was no significant difference in systolic blood pressure (BP) and heart rate between the two groups. TPs-SD was significantly higher in patients with LVH at rest (31.5 ± 12.1 vs. 22.0 ± 12.6 ms, p = 0.002) with exaggeration of the degree at peak exercise (39.0 ± 11.9 vs. 24.6 ± 13.3 ms, p < 0.001). Multiple regression analysis showed LV mass index was independently associated with LV dyssynchrony at peak exercise (β = 0.515, p = 0.001) when controlled for age, sex, and systolic BP at peak exercise.

Conclusion

Intraventricular systolic dyssynchrony during exercise is significantly associated with the degree of LVH in hypertensive patients.

Myocardial tagging by cardiovascular magnetic resonance: evolution of techniques--pulse sequences, analysis algorithms, and applications

Cardiovascular magnetic resonance (CMR) tagging has been established as an essential technique for measuring regional myocardial function. It allows quantification of local intramyocardial motion measures, e.g. strain and strain rate. The invention of CMR tagging came in the late eighties, where the technique allowed for the first time for visualizing transmural myocardial movement without having to implant physical markers. This new idea opened the door for a series of developments and improvements that continue up to the present time. Different tagging techniques are currently available that are more extensive, improved, and sophisticated than they were twenty years ago. Each of these techniques has different versions for improved resolution, signal-to-noise ratio (SNR), scan time, anatomical coverage, three-dimensional capability, and image quality. The tagging techniques covered in this article can be broadly divided into two main categories: 1) Basic techniques, which include magnetization saturation, spatial modulation of magnetization (SPAMM), delay alternating with nutations for tailored excitation (DANTE), and complementary SPAMM (CSPAMM); and 2) Advanced techniques, which include harmonic phase (HARP), displacement encoding with stimulated echoes (DENSE), and strain encoding (SENC). Although most of these techniques were developed by separate groups and evolved from different backgrounds, they are in fact closely related to each other, and they can be interpreted from more than one perspective. Some of these techniques even followed parallel paths of developments, as illustrated in the article. As each technique has its own advantages, some efforts have been made to combine different techniques together for improved image quality or composite information acquisition. In this review, different developments in pulse sequences and related image processing techniques are described along with the necessities that led to their invention, which makes this article easy to read and the covered techniques easy to follow. Major studies that applied CMR tagging for studying myocardial mechanics are also summarized. Finally, the current article includes a plethora of ideas and techniques with over 300 references that motivate the reader to think about the future of CMR tagging.

Heterogeneity of apex-to-base dispersion in diastolic lengthening is related to impaired global left ventricular relaxation in patients with hypertrophic cardiomyopathy

BACKGROUND

The presence of apex-to-base disparity in diastolic left ventricle (LV) endocardial lengthening, based on an electromechanical activation sequence, has been recognized as an important determinant of LV diastolic properties. However, the behavior of LV apical and basal diastolic lengthening and its relationship to LV filling in hypertrophic cardiomyopathy (HCM) are unknown.

METHODS

We obtained basal and apical LV short-axis views in 27 patients with non-obstructive HCM and 25 healthy volunteers. The patients with HCM were subdivided into two groups; those with apical hypertrophy [APH(+)] or those without apical hypertrophy [APH(-)]. Eight equiangular points on the endo-myocardium at end diastole were placed in each view, and the movements of these points were automatically tracked using a two-dimensional echocardiographic tissue tracking system. Time-LV internal diameter curves were obtained and averaged. The time intervals from the aortic valve closure to the point of the first 40% of peak diastolic lengthening (T 40) were measured in each view. The standard deviation of the time to peak systolic circumferential shortening at the base and apex were calculated to assess the heterogeneity of LV contraction.

RESULTS

The time difference in the T 40 between the apex and base (dt-T 40) in the HCM-APH(+) and HCM-APH(-) groups was greater than that in the control group. The heterogeneities in LV apical systolic shortening in the HCM groups were greater than those in the control group. There were good linear correlations between the dt-T 40 and the LV early diastolic echo-parameters and the LV mass index.

CONCLUSIONS

Delayed apical relaxation and filling in patients with HCM is related to LV diastolic dysfunction and systolic dyssynchronous contraction.

Cardiac MRI evaluation of nonischemic cardiomyopathies

The purpose of this manuscript is to review the major MRI findings in patients with nonischemic cardiomyopathies. Cardiac MRI has become an integral part in the diagnosis and management of patients with nonischemic cardiomyopathies. Findings on cardiac MRI studies can help distinguish between different types of cardiomyopathies and can provide valuable diagnostic and prognostic information.

Myocardial tissue tagging with cardiovascular magnetic resonance

Cardiovascular magnetic resonance (CMR) is currently the gold standard for assessing both global and regional myocardial function. New tools for quantifying regional function have been recently developed to characterize early myocardial dysfunction in order to improve the identification and management of individuals at risk for heart failure. Of particular interest is CMR myocardial tagging, a non-invasive technique for assessing regional function that provides a detailed and comprehensive examination of intra-myocardial motion and deformation. Given the current advances in gradient technology, image reconstruction techniques, and data analysis algorithms, CMR myocardial tagging has become the reference modality for evaluating multidimensional strain evolution in the human heart. This review presents an in depth discussion on the current clinical applications of CMR myocardial tagging and the increasingly important role of this technique for assessing subclinical myocardial dysfunction in the setting of a wide variety of myocardial disease processes.

Hypertrophic Cardiomyopathy Is Associated with More Severe Left Ventricular Dyssynchrony than Is Hypertensive Left Ventricular Hypertrophy

OBJECTIVE

To evaluate left ventricular (LV) dyssynchrony in patients with left ventricular hypertrophy (LVH), and to compare abnormalities associated with hypertrophic cardiomyopathy (HCM) and hypertensive heart disease (HHD) using 2D speckle tracking imaging.

METHODS

Basal, middle, and apical 2D LV short-axis images were acquired in 43 patients with LVH including 20 with HCM and 23 with HHD, and in 15 age-matched controls. Radial strain, circumferential strain, time interval from the R-wave to peak radial strain (Trs), and time to peak circumferential strain (Tcs) were measured in six equidistant segments at each level of the 3 LV short-axis views using 2D speckle tracking analysis. To assess LV dyssynchrony, Trs(cs)-18SD, the standard deviation (SD) of Trs(cs) in all 18 segments, was calculated.

RESULTS

Regional radial strain in the middle and apical short-axis segments was significantly less in patients with HCM than in those with HHD. Regional circumferential strain in the apical short-axis segments was also less in HCM. Trs-18SD and Tcs-18SD were significantly longer in patients with HCM than in age-matched controls and patients with HHD (Trs-18SD: HCM: 88 +/- 32 ms, HHD: 51 +/- 20 ms, control: 45 +/- 12 ms P < 0.001, Tcs-18SD: HCM: 71 +/- 27 ms, HHD: 46 +/- 14 ms, control: 45 +/- 14 ms P < 0.001).

CONCLUSIONS

The presence of LVH is thus not always associated with LV dyssynchrony. However, the greater reduction of regional strain and severe LV dyssynchrony in HCM may contribute to the adverse cardiovascular outcomes associated with this disease.

Myocardial strain and torsion quantified by cardiovascular magnetic resonance tissue tagging: studies in normal and impaired left ventricular function

Accurate quantification and timing of regional myocardial function allows early identification of dysfunction, and therefore becomes increasingly important for clinical risk assessment, patient management, and evaluation of therapeutic efficacy. For this purpose, the application of tissue Doppler echocardiography has rapidly increased. However, echocardiography has some major inherent limitations. Cardiovascular magnetic resonance imaging with tissue tagging provides highly reproducible data on myocardial function, not only in longitudinal and radial directions, but also in the circumferential direction. Because of the development of faster imaging protocols, improved temporal resolution, less time-consuming postprocessing procedures, and the potential of quantifying myocardial deformation in 3 dimensions at any point in the heart, this technique may serve as an alternative for tissue Doppler echocardiography and is now ready for more widespread clinical use. This review discusses the clinical use of cardiovascular magnetic resonance tissue tagging for quantitative assessment of regional myocardial function, thereby underlining the specific features and emerging role of this technique.

Global and Regional Myocardial Function Quantification by Two-Dimensional Strain

OBJECTIVES

Recently, a novel method to measure strain from standard two-dimensional images has been developed. Our goal was to characterize global and regional systolic function abnormalities using this technique in patients with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Strain has been proposed as a sensitive tool to detect early systolic function abnormalities in HCM. However, the clinical application of conventional Doppler-derived strain has been limited by poor reproducibility and angle dependency.

METHODS

Echocardiographic examinations were performed in 26 patients with nonobstructive HCM and 45 healthy subjects. Using a dedicated software package, bidimensional acquisitions were analyzed to measure longitudinal and transverse strain in apical views and circumferential and radial strain in parasternal short-axis view.

RESULTS

Despite apparently normal left ventricular systolic function, all components of strain were significantly reduced in HCM. Average longitudinal, transverse, circumferential, and radial strain in patients with HCM and controls were -15.1 +/- 6.2% versus -20.3 +/- 5.6%, 23.3 +/- 17.0% versus 27.2 +/- 14.9%, -16.8 +/- 7.1% versus 19.6 +/- 5.2%, and 25.2 +/- 13.9% versus 36.8 +/- 17.2%, respectively (all p < 0.001). In patients with asymmetrical HCM, longitudinal septal strain was significantly lower than for other left ventricular segments combined: -9.2 +/- 4.7% versus -12.7 +/- 7.1% (p = 0.001). Average interobserver and intraobserver variabilities were 11% and 11.3%, respectively.

CONCLUSIONS

Two-dimensional strain is a new simple, rapid, and reproducible method to measure different components of systolic strain. This technique identified early abnormalities in patients with HCM that have apparently normal left ventricular systolic function.

First-pass myocardial perfusion defect and delayed contrast enhancement in hypertrophic cardiomyopathy assessed with MRI

BACKGROUND

Gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) enhanced magnetic resonance imaging (MRI) is known to be useful for detecting myocardial injury. In this study, we used first-pass myocardial perfusion and delayed contrast-enhanced MRI to determine whether an abnormal signal intensity was related to the left ventricular regional contractile function in patients with hypertrophic cardiomyopathy (HCM).

MATERIALS AND METHODS

Twelve patients with HCM participated in this study. Four short axial cine images of the left ventricle were acquired. Subsequently, first-pass myocardial perfusion images during the first passage of Gd-DTPA (0.1 mmol/kg), and delayed contrast-enhanced images after a 15-min delay, were acquired in the same orientation as cine imaging. Each image was divided into eight blocks and a total of 384 blocks were analyzed.

RESULTS

First-pass myocardial perfusion defects (PD) were detected in nine patients with an average of 11.5+/-11 blocks. Delayed contrast enhancement (DE) was detected in 11 patients with an average of 11.5+/-10 blocks. Mean wall thickness in PD blocks (16.7+/-4.7 mm) was larger than that in normal perfusion blocks (13.6+/-3.9 mm, p<0.001). Mean wall thickness in DE blocks (16.9+/-4.9 mm) was larger than that in normal enhanced blocks (13.4+/-3.6 mm, p<0.001). PD were located at almost the same site as DE, but DE areas were larger than PD areas (p=0.0021). Mean percent wall thickening of blocks with PD (63.1+/-44.7%, p<0.0001) and blocks with DE (75.2+/-81.5%, p<0.01) was lower than that in blocks with neither PD nor DE (103.5+/-66.0%). Significant correlations were found between percent wall thickening and percent PD (r=0.46, p<0.0001) and between percent wall thickening and percent DE (r=0.54, p<0.0001).

CONCLUSION

Abnormal signal intensity from first-pass myocardial perfusion and delayed contrast-enhanced MRI are closely related to left ventricular regional contractile function.

Prevalence and clinical significance of systolic impairment in hypertrophic cardiomyopathy

OBJECTIVES

To determine the frequency of systolic impairment (SI) and its impact on the natural history of hypertrophic cardiomyopathy (HCM).

METHODS

1080 patients (mean (SD) age 43 (15) years, 660 men) with HCM were evaluated. Initial assessment included history, examination, 48 hour Holter monitoring, cardiopulmonary exercise testing, and echocardiography; SI was defined as a fractional shortening (FS) < or = 25%. Survival data were collected at clinic visits or by direct communication with patients and their general practitioners. The results of serial echocardiography in 462 patients with normal FS at presentation are also reported.

RESULTS

26 (2.4%) patients (49 (14) years, 18 men) had SI at the initial visit. During follow up (58 (49) months), nine (34.6%) died or underwent cardiac transplantation compared with 108 (10.2%) patients with normal FS (p = 0.01). Five year survival from death (any cause) or transplantation was 90.1% (95% confidence interval (CI) 87.8 to 92.4) in patients with normal systolic function versus 52.4% (95% CI 25.2 to 79.6, p < 0.0001) in patients with SI. In patients who underwent serial echocardiography, 22 (4.8%, aged 41 (15) years) developed SI over 66 (40) months; the annual incidence of SI was 0.87% (95% CI 0.54 to 1.31). On initial evaluation patients who developed SI had a higher frequency of syncope (67 (15.2%) v 10 (45.5%) of those who did not develop SI, p = 0.001), non-sustained ventricular tachycardia (91 (20.6%) v 11 (50%), p = 0.002), and an abnormal blood pressure response on exercise (131 (29.7%) v 15 (68.2%), p = 0.001). Patients with SI had greater wall thinning (p = 0.001), left ventricular cavity enlargement (p < 0.0005), and deterioration in New York Heart Association functional class (p = 0.001) during follow up. Thirteen (59.1%) patients who progressed to SI died or underwent transplantation compared with 38 (8.6%) patients who maintained normal systolic function.

CONCLUSIONS

SI is an infrequent complication of HCM but, when present, is associated with a poor prognosis.

Quantification of Regional Nonuniformity and Paradoxical Intramural Mechanics in Hypertrophic Cardiomyopathy by High Frame Rate Ultrasound Myocardial Strain Mapping

This study tested the hypothesis that linear mapping of regional myocardial strain comprehensively assesses variations in regional myocardial function in hypertrophic cardiomyopathy. Hypertrophic cardiomyopathy is characterized by disorganized myocardial architecture that results in spatial and temporal nonuniformity of regional function. Left ventricular deformation was quantified in 20 patients with hypertrophic cardiomyopathy and compared with 25 age- and sex-matched control subjects. Abnormalities in subendocardial strain ranged from reduced longitudinal shortening to paradoxical systolic lengthening and delayed regional longitudinal contractions that were often located in small subsegmental areas. These variations were underestimated significantly by arbitrary measurements compared with linear mapping, in which a region of interest was moved across the longitudinal length of left ventricle (difference of peak and least strain, 10.7% +/- 5.1% vs 17% +/- 5.5%; P < .001). Echocardiographic assessment of variations in regional strain requires careful mapping and may be inappropriately assessed if left ventricular segments are sampled at arbitrary focal locations.

Use of angiotensin II stress pulsed tissue Doppler imaging to evaluate regional left ventricular contractility in patients with hypertrophic cardiomyopathy

There is controversy concerning whether contract-ility in the nonhypertrophied region of the left ventricular (LV) wall is impaired or normal in patients with hypertrophic cardiomyopathy (HCM). Global LV systolic function decreases with increases in afterload in this disease. This study was performed to identify abnormalities in regional LV contractility along the long and short axes in the setting of HCM with the use of angiotensin II (AT-II) stress pulsed tissue Doppler imaging (PTDI). Angiotensin II was administered intravenously to patients with asymmetric septal hypertrophy (HCM group, n = 21) and age-matched normal volunteers (N group, n = 12). We then measured the percent LV fractional shortening (%FS) and end-systolic circumferential LV wall stress by M-mode echocardiography, LV ejection fraction (LVEF) by 2-dimensional echocardiography, and time-velocity integral (TVI) of LV outflow velocity by pulsed Doppler echocardiography. The peak first and second systolic LV wall motion velocities along the long (L-Sw(1) and L-Sw(2)) and short (S-Sw(1) and S-Sw(2)) axes were measured in the LV posterior wall and ventricular septum with the use of PTDI. The end-systolic circumferential LV wall stress at baseline was significantly lower in the HCM group. The L-Sw(1) and L-Sw(2) for the posterior wall were significantly lower in the HCM group, but the S-Sw(1) and S-Sw(2) for the posterior wall and ventricular septum were similar in the two groups. The %FS, LVEF, TVI, and systolic PTDI variables along both axes for the posterior wall decreased significantly, and end-systolic circumferential LV wall stress increased significantly at AT-II doses of 0.005 or 0.010 microg/kg per minute in the HCM group. No significant changes were found in either group in the systolic PTDI variables (except for L-Sw(1)) for the ventricular septum with AT-II infusion. Contractility along the long and short axes of the nonhypertrophied LV wall is easily impaired with increases in afterload in patients with HCM, resulting in a decrease in global LV systolic function. We found AT-II stress PTDI to be a safe and useful technique for evaluating the regional LV systolic function in this disease.

A transgenic rabbit model for human hypertrophic cardiomyopathy

Certain mutations in genes for sarcomeric proteins cause hypertrophic cardiomyopathy (HCM). We have developed a transgenic rabbit model for HCM caused by a common point mutation in the beta-myosin heavy chain (MyHC) gene, R400Q. Wild-type and mutant human beta-MyHC cDNAs were cloned 3' to a 7-kb murine beta-MyHC promoter. We injected purified transgenes into fertilized zygotes to generate two lines each of the wild-type and mutant transgenic rabbits. Expression of transgene mRNA and protein were confirmed by Northern blotting and 2-dimensional gel electrophoresis followed by immunoblotting, respectively. Animals carrying the mutant transgene showed substantial myocyte disarray and a 3-fold increase in interstitial collagen expression in their myocardia. Mean septal thicknesses were comparable between rabbits carrying the wild type transgene and their nontransgenic littermates (NLMs) but were significantly increased in the mutant transgenic animals. Posterior wall thickness and left ventricular mass were also increased, but dimensions and systolic function were normal. Premature death was more common in mutant than in wild-type transgenic rabbits or in NLMs. Thus, cardiac expression of beta-MyHC-Q(403) in transgenic rabbits induced hypertrophy, myocyte and myofibrillar disarray, interstitial fibrosis, and premature death, phenotypes observed in humans patients with HCM due to beta-MyHC-Q(403).