Comparison of Two Murine Models of Familial Hypertrophic Cardiomyopathy
Abstract—Although sarcomere protein gene mutations cause familial hypertrophic cardiomyopathy (FHC), individuals bearing a mutant cardiac myosin binding protein C (MyBP-C) gene usually have a better prognosis than individuals bearing β-cardiac myosin heavy chain (MHC) gene mutations. Heterozygous mice bearing a cardiac MHC missense mutation (αMHC403/+ or a cardiac MyBP-C mutation (MyBP-Ct/+) were constructed as murine FHC models using homologous recombination in embryonic stem cells. We have compared cardiac structure and function of these mouse strains by several methods to further define mechanisms that determine the severity of FHC. Both strains demonstrated progressive left ventricular (LV) hypertrophy; however, by age 30 weeks, αMHC403/+ mice demonstrated considerably more LV hypertrophy than MyBP-Ct/+ mice. In older heterozygous mice, hypertrophy continued to be more severe in the αMHC403/+ mice than in the MyBP-Ct/+ mice. Consistent with this finding, hearts from 50-week-old αMHC403/+ mice demonstrated increased expression of molecular markers of cardiac hypertrophy, but MyBP-Ct/+ hearts did not demonstrate expression of these molecular markers until the mice were >125 weeks old. Electrophysiological evaluation indicated that MyBP-Ct/+ mice are not as likely to have inducible ventricular tachycardia as αMHC403/+ mice. In addition, cardiac function of αMHC403/+ mice is significantly impaired before the development of LV hypertrophy, whereas cardiac function of MyBP-Ct/+ mice is not impaired even after the development of cardiac hypertrophy. Because these murine FHC models mimic their human counterparts, we propose that similar murine models will be useful for predicting the clinical consequences of other FHC-causing mutations. These data suggest that both electrophysiological and cardiac function studies may enable more definitive risk stratification in FHC patients.
Familial hypertrophic cardiomyopathy (FHC) is inherited as an autosomal dominant trait that is characterized by myocardial hypertrophy in the absence of identifiable precipitating hemodynamic factors.1 2 The diagnostic hallmark of FHC is asymmetric hypertrophy of the interventricular septum; however, the distribution and severity of hypertrophy are variable.3 4 Affected individuals may present with symptoms ranging from dizziness and palpitations to sudden death. Molecular genetic studies have demonstrated that FHC is genetically heterogeneous; 10 disease genes have been identified.2 5 All 10 of these genes encode sarcomere proteins expressed in cardiac muscle. We and others have demonstrated that individuals bearing some sarcomere protein gene mutations have better prognoses than individuals bearing other mutations,6 7 8 but the basis for this correlation has not been elucidated.
To further investigate factors determining the clinical response to a sarcomere protein gene mutation, we have created two strains of mice, using homologous recombination in embryonic stem cells that bear precise analogues of FHC-causing mutations. Individuals bearing the β-cardiac myosin heavy chain (MHC) gene Arg403Gln missense mutation have an earlier disease onset and a shorter life expectancy than individuals bearing mutations in the cardiac myosin binding protein C (MyBP-C) gene.7 8 Transgenic mice expressing cDNAs encoding mutant forms of both MyBP-C and MHC have been produced previously.9 10 These mice are of limited value for directly comparing the consequences of FHC-causing mutations because the amount and temporal pattern of mutant cDNA expression, even when controlled by a cardiac specific promoter, varies even between different strains of mice bearing the same mutant transgene. We have previously created a mouse bearing the Arg403Gln mutation in one allele of the α-cardiac MHC gene, the murine analogue of the human β-cardiac MHC gene.11 Heterozygous Arg403Gln α-cardiac MHC (αMHC403/+) mutant mice have been shown to develop physiological and histological features typical of human FHC.11 12 13 Recently, we created a strain of mice bearing a neomycin resistance gene inserted in the cardiac MyBP-C gene.14 This mutant allele encodes a truncated MyBP-C protein that closely resembles the truncated MyBP-C protein that causes FHC in some individuals (Family NN in Figure 1A⇓ and Reference1414 ); heterozygous mice bearing the mutant allele were designated MyBP-Ct/+ mice. Although we have previously demonstrated that both homozygous αMHC403/403 and MyBP-Ct/t mice produce mutant polypeptides and develop dilated cardiomyopathy, the cardiac phenotype of older heterozygous mice bearing these mutations has not been compared.
We have characterized cardiac structure and function of αMHC403/+ and MyBP-Ct/+ mice at several ages to define the development of hypertrophic cardiomyopathy in these mice. We demonstrate in the present study that both mutations cause cardiac hypertrophy. However, αMHC403/+ mice develop hypertrophy much earlier than MyBP-Ct/+ mice consistent with the pathologies observed in humans bearing these mutations. In addition, we demonstrate that hearts bearing truncated MyBP-C polypeptide have normal cardiac function and do not demonstrate inducible ventricular tachycardia whereas age-matched hearts bearing α-cardiac MHC Arg403Gln missense polypeptide have significant deficits in cardiac and electrophysiological function.12 15 We speculate that deficits in cardiac function, rather than increased cardiac hypertrophy, are responsible for the more severe symptoms observed in individuals with the Arg403Gln missense mutation.
Materials and Methods
Mice bearing the MyBP-C(Neo) allele were generated using homologous recombination techniques and a targeting construct containing exons 28 to 32 of the murine cardiac MyBP-C gene with a 2-kb neomycin gene insertion in exon 30 as described.14 Heterozygous mice bearing the MyBP-C(Neo) allele are designated MyBP-Ct/+. The structure of mutant-derived MyBP-C RNA was defined by reverse transcription–polymerase chain reaction (RT-PCR) amplification and DNA sequencing of RNA derived from homozygous mice bearing the MyBP-C(Neo) allele.14 Mouse genotypes were determined by PCR amplification or restriction enzyme digestion of tail DNA from each animal.11 14 αMHC403/+ mice were generated as described.11 Both strains of mice were bred and maintained on the 129SvEv genetic background. Electrophysiological analyses were performed on mice bearing these mutations on a 129/BS genetic background. All mice were maintained according to protocols approved by the Institutional Animal Care and Use Committee of Harvard Medical School.
Cardiac Physiology and Pathology
Cardiac tissues from male mice were subjected to histological examination using methods described previously.11 16 A single experienced pathologist who was unaware of the mouse genotype reviewed all histological specimens.
Echocardiographic studies were performed on male mice using a 12-MHz linear array probe with a Sonos 5500 ultrasonograph (Hewlett-Packard) as described.14 Left ventricular (LV) end-diastolic (LVDD) and end-systolic (LVSD) chamber dimensions and wall thickness were obtained from M-mode tracings using measurements averaged from 3 separate cardiac cycles. LV fractional shortening (%) was derived as follows: (LVDD−LVSD)/LVDD×100. A single observer, who did not know the mouse’s genotype, made all echocardiographic measurements. Heart rates were determined from electrocardiographic recordings performed during echocardiography.
LV hemodynamic studies were performed in male mice as described previously.12 17 In brief, anesthetized mice were intubated, artificially ventilated, and real-time LV pressure-volume relationships were measured using a newly developed miniaturized impedance/micromanometer catheter (Millar Instruments). Aortic flow was measured by an ultrasound perivascular probe (Transonics, 1RB) placed around the thoracic aorta. Pressure-volume signals were recorded at steady state and during transient reduction of cardiac preload achieved by inferior vena caval occlusion. Data were digitized at 2 kHz for subsequent analysis.
Surface resting electrocardiograms and electrophysiological studies were performed in anesthetized male wild-type and αMHC403/+ mice as described.15 18 Standard procedures for pacing and extra-stimulus testing were used to assess baseline conduction parameters and arrhythmia induction.15 18 The PR, QRS, RR, and QT intervals were measured in 6 surface limb ECG leads by two independent observers who were blinded to mouse genotype. Inducible ventricular tachycardia was assessed as described previously.18 19
RNA and Protein Analyses
Northern blot analyses were performed as described previously.14 20 Total RNA was isolated from the left ventricle using Trizol (Gibco BRL) and analyzed by standard Northern blot procedures.14 MyBP-C RNA was detected using 32P-labeled insert from a 2.4-kb mouse MyBP-C cDNA plasmid clone designated pcMyBPC. The MyBP-C cDNA probe consisted of a 1584-bp segment encoding amino acid residues 582 to 1110.14 Other RNAs were detected using 5′-32P-labeled oligonucleotide probes and hybridized to nylon membranes using standard hybridization conditions.14 The oligonucleotides used as transcript specific probes were as follows:
atrial natriuretic factor: 5′-AATGTGACCAAGCTGCGTGACACACCACAAGGGCTTAGGATCTTTTGC-3′
brain natriuretic factor: 5′-CAGCTTGAGATATGTGTCACCTTGGAATTTTGAGGTCTC-TGCTGGACC-3′
α-skeletal actin: 5′-TGGCTTTAATGCTTCAAGTTTTCCATTTCCTTTCCACAG-GG-3′
The hybridization signal for each oligonucleotide probe was quantified using ImageQuant software (Molecular Dynamics) and normalized to the signal intensity observed with an oligonucleotide specific for GAPDH RNA. MyBP-C polypeptides were identified by Western blot analyses using antibody raised against chicken cardiac MyBP-C.14
The statistical significance of differences between groups of wild-type, MyBP-Ct/+, and αMHC403/+ mice in continuous variables was determined by one-factor ANOVA and the unpaired Student’s t test. Differences in categorical variables were assessed with the χ2 test. Data are expressed as mean±SD. A value of P<0.05 was considered significant.
Expression and Structure of RNAs and Proteins Expressed in MyBP-Ct/+ and αMHC403/+ Hearts
MyBP-C mRNA expressed from the MyBP-C(Neo) allele was characterized by Northern blot analyses of heterozygous MyBP-Ct/+ cardiac RNA (Figures 1A⇑ and 1B⇑). The 4.5-kb MyBP-C RNA transcript was found in the left ventricle of both wild-type and MyBP-Ct/+ mice; however, MyBP-C mRNA expression in MyBP-Ct/+ mice (n=6) was 49.2±16.6% the level of expression in wild-type mice (n=6). MyBP-C (150 kDa) protein was identified in myofibrillar extracts from cardiac left ventricles of wild-type and MyBP-Ct/+ mice. MyBP-C (mutant and wild type) protein expression in MyBP-Ct/+ left ventricles (n=4) was 89.9±8.5% the level found in wild-type left ventricles. Because the mutant MyBP-C(Neo) allele produces a reduced amount (10% of wild type) of truncated MyBP-C peptide,14 we hypothesize that the heterozygous MyBP-Ct/+ hearts contain ≈90% wild-type MyBP-C and 10% truncated peptide.
The structure of the carboxyl end of the MyBP-C polypeptide encoded by the MyBP-C(Neo) allele was characterized by nucleotide sequence analyses of RT-PCR–amplified products derived from RNA found in the left ventricle of homozygous MyBP-Ct/t mice (Figure 1A⇑ and Reference1414 ). αMHC403/+ left ventricles contain equivalent amounts of mutant and wild-type α-cardiac MHC mRNA and protein (our unpublished results).
Previous studies11 demonstrated that hearts from 15-week-old αMHC403/+ mouse hearts have mild myocyte hypertrophy, interstitial fibrosis, and myofibrillar disarray that become much more severe by 30 to 50 weeks of age. No histological abnormalities were observed in 50-week-old MyBP-Ct/+ mouse hearts. Histological sections obtained from >125-week-old MyBP-Ct/+ mouse hearts demonstrated myocyte hypertrophy, interstitial fibrosis, and myofibrillar disarray in ≈50% of mutant animals. However, similar histological abnormalities were observed in a comparable proportion of hearts from age-matched wild-type mice (Figure 2⇓ and data not shown).
Cardiac Morphology of Mutant and Wild-Type Mice
Cardiac hypertrophy in mutant and wild-type mice was assessed using transthoracic echocardiography (Table 1⇓). Neither 10- to 20-week-old male MyBP-Ct/+ or αMHC403/+ mouse hearts demonstrated significant differences from age-matched wild-type mouse hearts (Table 1⇓). By 30 to 50 weeks, both MyBP-Ct/+ mice and αMHC403/+ mice were beginning to demonstrate signs of their mutations. MyBP-Ct/+ mice displayed significantly enlarged atria and a slight increase in LV wall thickness compared with wild-type mice (0.96±0.08 versus 0.87±0.05 mm; P<0.05). However, αMHC403/+ mice demonstrated significantly increased left atrial dimensions and much greater LV wall thickness than either MyBP-Ct/+ or wild-type mice (compare left ventricular anterior wall thickness [LVAW] of αMHC403/+ mice, 1.12±0.07 mm versus LVAW of wild-type, 0.87±0.06 mm, and MyBP-Ct/+, 0.96±0.08 mm, mice; P<0.05; Table 1⇓). In addition, only 32% (6 of 19) of the MyBP-Ct/+ mice had developed cardiac hypertrophy (>1.0 mm) by 50 weeks of age (Figure 3⇓) compared with 92% (11 of 12) αMHC403/+ mice. However, LVAW of >125-week-old MyBP-Ct/+ mice was significantly greater than age-matched wild-type mice (1.39±0.10 versus 1.08±0.05 mm, P<0.001; Table 1⇓), demonstrating that cardiac hypertrophy is late onset in heterozygous MyBP-C mutant mice. The fractional shortening was not significantly different in MyBP-Ct/+ mice (55±4%) compared with age-matched wild-type mice (52±5%) at >125 weeks. Heart rates during echocardiographic studies were similar in all groups of mice (Table 1⇓ and data not shown). (The different heart rates of age- and strain-matched mice reported in Tables 1⇓ and 2⇓ are due to differences in anesthesia used in different studies.)
LV Pressure-Volume Analyses
Previous studies have demonstrated that 8- to 20-week-old αMHC403/+ mice have impaired cardiac function compared with age-matched wild-type mice.12 We demonstrate in the present study that 30- to 50-week-old αMHC403/+ mice, like 20-week-old αMHC403/+ mice, exhibited altered LV diastolic kinetics with delayed pressure relaxation and chamber filling (Table 2⇑). Thirty to 50-week-old αMHC403/+ mice also had altered elevated LV systolic pressure (Table 2⇑).
Cardiac function of wild-type and MyBP-Ct/+ mice at 30 to 50 weeks and >125 weeks were assessed by in vivo cardiac catheterization (Figure 4⇓). Thirty to 50-week-old MyBP-Ct/+ mice had normal systolic and diastolic LV function when compared with age-matched wild-type mice (Table 2⇑ and data not shown). Similarly, cardiac function of >125-week-old MyBP-Ct/+ mice was indistinguishable from that of age-matched wild-type mice but significantly better than cardiac function of 30- to 50-week-old αMHC403/+ mice (Figure 4⇓, Table 2⇑, and data not shown).
Baseline recordings in 30- to >125-week-old MyBP-Ct/+ mice showed the same electrocardiographic interval conduction times and axes as observed in age-matched wild-type mice (data not shown). Neither MyBP-Ct/+ nor αMHC403/+ mice exhibited PR prolongation, AV block, or abnormally long atrioventricular conduction block coupling intervals. Normal atrial and ventricular conduction parameters and refractory periods were also demonstrated in both strains of mice (data not shown and Reference 2020 ). Using a standard murine pacing and programmed electrical stimulation protocol,15 18 19 inducible arrhythmias were elicited in significantly more (8 of 15) 30- to 50-week-old αMHC403/+ mice than age-matched wild-type (0 of 10) or MyBP-Ct/+ (1 of 9) mice. Similar proportions of >125-week-old MyBP-Ct/+ (2 of 6) and wild-type (2 of 4) mice demonstrated inducible arrhythmias.
RNA Expression Associated With Cardiomyopathy
Atrial natriuretic factor, brain natriuretic factor, and α-skeletal actin mRNAs, which are induced in other models of cardiac hypertrophy, were measured in mutant mice at 10 to 20, 30 to 50, and >125 weeks of age by Northern blot analyses. The amounts of atrial natriuretic factor, brain natriuretic factor, and α-skeletal actin RNA transcripts in 10- to 20-week-old αMHC403/+ and MyBP-Ct/+ hearts were the same as in age-matched wild-type hearts (data not shown). However, by 50 weeks, αMHC403/+ left ventricles demonstrated increases in atrial natriuretic factor (4.9±1.0-fold), brain natriuretic factor (2.5±0.3-fold), and α-skeletal actin (1.9±0.2-fold) RNAs compared with 50-week-old wild-type left ventricles (Figure 5⇓). Left ventricles from 50-week-old MyBP-Ct/+ mice had the same amounts of these RNAs as left ventricles from age-matched wild-type mice. However, left ventricles of >125-week-old MyBP-Ct/+ mice demonstrated significant increases in atrial natriuretic factor (3.1±0.4-fold), brain natriuretic factor (2.3±0.2-fold), and α-skeletal actin (3.3±0.7-fold) RNAs compared with left ventricles from age-matched wild-type hearts (Figure 5⇓).
We demonstrate that both αMHC403/+ and MyBP-Ct/+ mice, two strains of mice bearing different FHC-causing mutations, develop LV hypertrophy, but age-matched αMHC403/+ mice have much more LV hypertrophy than MyBP-Ct/+ mice. Mice bearing the Arg403Gln missense mutation in the α-cardiac MHC gene have impaired cardiac function (Figure 4⇑ and References 11 and 1211 12 ) and some have electrophysiological abnormalities. However, no difference in cardiac function of mice expressing the truncated cardiac MyBP-C gene and wild-type mice was detected (Figure 4⇑ and Table 2⇑) and neither demonstrated inducible arrhythmias. These observations may explain the different clinical features observed in humans bearing different sarcomere protein gene mutations. Although the mechanisms by which these mutations cause hypertrophy remain uncertain, some insights into this process can be gained by considering the effects of these different mutations on cardiac function and LV morphology.
Both heterozygous αMHC403/+ and MyBP-Ct/+ mice develop LV hypertrophy, whereas homozygous αMHC403/+ and MyBP-Ct/t mice develop dilated cardiomyopathy.14 16 Homozygous αMHC403/+ mice develop severe dilated cardiomyopathy and die by day 10 after birth16 whereas MyBP-Ct/t mice develop a milder dilated cardiomyopathy and survive for up to 2 years.14 Thus, the severity of dilated cardiomyopathy in homozygous mice bearing sarcomere protein mutations paralleled the severity of hypertrophic cardiomyopathy observed in heterozygous mice bearing the same mutations. Perhaps the signal that determines the severity of dilated cardiomyopathy in homozygous mutant mice is the same signal that determines the severity of LV hypertrophy in heterozygous mutant mice.
Young αMHC403/+ mice have cardiac dysfunction12 and this dysfunction is also found in older αMHC403/+ mice (Table 2⇑). Thus, cardiac dysfunction precedes cardiac hypertrophy in these mice (Table 1⇑ and Figures 3⇑ and 4⇑). We conclude that cardiac dysfunction is not secondary to the cardiac hypertrophy, myocyte disarray, myocyte hypertrophy, and fibrosis observed in older αMHC403/+ mice. Previous studies21 22 23 have suggested that sarcomere dysfunction per se can lead to cardiac hypertrophy. Are the findings demonstrated in the present study consistent with this model? αMHC403/+ mice who develop cardiac hypertrophy by age 30 weeks (Table 1⇑) have defective sarcomere function24 25 and significant cardiac dysfunction11 12 13 (see Table 2⇑). However, cardiac function of the MyBP-Ct/+ mice (Table 2⇑ and Figure 4⇑) appears normal, and we anticipate that sarcomere dysfunction will be minimal. These animals do not develop cardiac hypertrophy until much later in life. Two hypotheses can be proposed: (1) that cardiac hypertrophy arises in MyBP-Ct/+ mice in the absence of cardiac dysfunction and (2) that MyBP-Ct/+ mice have very mild cardiac dysfunction that is not detectable by the methods used in the present study (see Materials and Methods). We strongly favor the latter model. We have demonstrated that these mice express a truncated cardiac MyBP-C in their myocardium and that homozygous mice expressing this mutation have significant cardiac dysfunction. Therefore, we suggest that cardiac dysfunction induces hypertrophy in these FHC models.
Electrophysiological abnormalities might contribute to the more severe disease process observed in αMHC403/+ mice. However, we do not know whether these abnormalities precede cardiac hypertrophy and its associated histopathological changes. Characterization of MyBP-Ct/+ mice suggests that cardiac hypertrophy can occur in mice without causing electrophysiological abnormalities because >125-week-old mutant animals were no more susceptible to inducible arrhythmias than >125-week-old wild-type mice. Previous studies of individuals with hypertrophic cardiomyopathy have suggested that electrophysiological abnormalities are not a good prognostic indicator in this disease.26 27 The findings reported in the present study suggest that some FHC-causing mutations cause more electrophysiological abnormalities than other FHC-causing mutations. Why one sarcomere gene mutation causes such abnormalities and not another sarcomere gene mutation remains uncertain.
The prognostic value derived from identification of FHC-causing mutations has been debated for the past several years.2 Physicians have recognized for the past two decades that some FHC-causing mutations cause more severe disease than other mutations. However, when a new mutation is identified in an individual, predicting whether this mutation will cause severe or mild disease in other family members is difficult. Characterization of murine FHC models suggests that one approach to this problem may be to introduce mutations into otherwise genetically identical mice and then study the phenotype of these murine models. We suggest that the strong correlation between murine phenotypes and clinical features observed in humans bearing analogous FHC-causing mutations will be observed in mice bearing other FHC-causing mutations. Further production and evaluation of other mouse strains bearing FHC-causing mutations should help to define the predictive value of these murine FHC models. Eventually, characterization of other murine FHC models will provide important prognostic information to patients and physicians. Another approach to the problem of predicting the severity of an FHC-causing mutation in humans is suggested by the results in the present study. Based on the two murine models, mutations that cause significant deficits in cardiac function cause severe disease whereas mutations that cause less impairment of cardiac function cause milder disease. Cardiac function of genetically affected family members should provide a good indicator of the clinical consequences of an FHC-causing mutation.
The Howard Hughes Medical Institute supported these studies. J.M. and M.H. were recipients of Sarnoff Foundation fellowships. C.S. and C.B. received National Heart Foundation of Australia and National Institutes of Health Grant K08-03607, respectively.
Original received October 23, 2000; resubmission received January 3, 2001; accepted January 23, 2001.
↵1 These authors contributed equally to this work.
This manuscript was sent to James T. Willerson, Consulting Editor, for review by expert referees, editorial decision, and final disposition.
- © 2001 American Heart Association, Inc.
Hunter JJ, Grace A, Chien KR. Molecular and cellular biology of cardiac hypertrophy and failure. In: Chien KR, ed. Molecular Basis of Cardiovascular Disease. Philadelphia, Pa: Saunders; 1999:211–250.
Fatkin D, Seidman JG, Seidman CE. Hypertrophic cardiomyopathy. In: Willerson JT, Cohn JN, eds. Cardiovascular Medicine. Philadelphia, Pa: Saunders; 2000:1055–1074.
Seidman CE, Seidman JG. Molecular genetic studies of familial hypertrophic cardiomyopathy. Basic Res Cardiol. 1998;93:13–16.
Niimura H, Bachinski LL, Sangwatanaroj S, Watkins H, Chudley AE, McKenna W, Kristinsson A, Roberts R, Sole M, Maron BJ, Seidman JG, Seidman CE. Mutations in the gene for cardiac myosin-binding protein C and late-onset familial hypertrophic cardiomyopathy. N Engl J Med. 1998;338:1248–1257.
Charron P, Dubourg O, Desnos M, Bennaceur M, Carrier L, Camproux AC, Isnard R, Hagege A, Langlard JM, Bonne G, Richard P, Hainque B, Bouhour JB, Schwartz K, Komajda M. Clinical features and prognostic implications of familial hypertrophic cardiomyopathy related to the cardiac myosin-binding protein C gene. Circulation. 1998;97:2230–2236.
Geisterfer-Lowrance AA, Christe M, Conner DA, Ingwall JS, Schoen FJ, Seidman CE, Seidman JG. A mouse model of familial hypertrophic cardiomyopathy. Science. 1996;272:731–734.
McConnell BK, Jones KA, Fatkin D, Arroyo LH, Lee RT, Aristizabal O, Turnbull DH, Georgakopoulos D, Kass D, Bond M, Niimura H, Schoen FJ, Conner D, Fischman DA, Seidman CE, Seidman JG. Dilated cardiomyopathy in homozygous myosin-binding protein-C mutant mice. J Clin Invest. 1999;104:1235–1244.
Berul CI, Mendelsohn ME. Molecular biology and genetics of cardiac disease associated with sudden death: electrophysiologic studies in mouse models of inherited diseases. In: Estes NAM, Salem DN, Wang PJ, eds. Sudden Cardiac Death in the Athlete. Armonk, NY: Futura Publishing Co; 1998:465–481.
Baan J, van der Velde ET, de Bruin HG, Smeenk GJ, Koops J, van Dijk AD, Temmerman D, Senden J, Buis B. Continuous measurement of left ventricular volume in animals and humans by conductance catheter. Circulation. 1984;70:812–823.
Berul CI, Aronovitz MJ, Wang PJ, Mendelsohn ME. In vivo cardiac electrophysiology studies in the mouse. Circulation. 1996;94:2641–2648.
McConnell BK, Moravec CS, Bond M. Troponin I phosphorylation and myofilament calcium sensitivity during decompensated cardiac hypertrophy. Am J Physiol. 1998;274:H385–H396.
Sweeney HL, Straceski AJ, Leinwand LA, Tikunov BA, Faust L. Heterologous expression of a cardiomyopathic myosin that is defective in its actin interaction. J Biol Chem. 1994;269:1603–1605.
Lankford EB, Epstein ND, Fananapazir L, Sweeney HL. Abnormal contractile properties of muscle fibers expressing β-myosin heavy chain gene mutations in patients with hypertrophic cardiomyopathy. J Clin Invest. 1995;95:1409–1414.
Blanchard E, Seidman C, Seidman JG, LeWinter M, Maughan D. Altered crossbridge kinetics in the αMHC403/+ mouse model of familial hypertrophic cardiomyopathy. Circ Res. 1999;84:475–483.
Kuck KH, Kunze KP, Schluter M, Nienaber CA, Costard A. Programmed electrical stimulation in hypertrophic cardiomyopathy: results in patients with and without cardiac arrest or syncope. Eur Heart J. 1988;9:177–185.