Mutational spectrum of the CHAC gene in patients with chorea-acanthocytosis

Chorea-acanthocytosis (ChAc) is an autosomal recessive neurological disorder whose characteristic features include hyperkinetic movements and abnormal red blood cell morphology. Mutations in the CHAC gene on 9q21 were recently found to cause chorea-acanthocytosis. CHAC encodes a large, novel protein with a yeast homologue implicated in protein sorting. In this study, all 73 exons plus flanking intronic sequence in CHAC were screened for mutations by denaturing high-performance liquid chromatography in 43 probands with ChAc. We identified 57 different mutations, 54 of which have not previously been reported, in 39 probands. The novel mutations comprise 15 nonsense, 22 insertion/deletion, 15 splice-site and two missense mutations and are distributed throughout the CHAC gene. Three mutations were found in multiple families within this or our previous study. The preponderance of mutations that are predicted to cause absence of gene product is consistent with the recessive inheritance of this disease. The high proportion of splice-site mutations found is probably a reflection of the large number of exons that comprise the CHAC gene. The CHAC protein product, chorein, appears to have a certain tolerance to amino-acid substitutions since only two out of nine substitutions described here appear to be pathogenic.

Dual chamber pacemaker therapy for mid-cavity obstructive hypertrophic cardiomyopathy

Intracavitary LV obstruction is an important determinant of clinical outcome in hypertrophic cardiomyopathy (HCM). In a minority of patients the obstruction is at the level of the papillary muscles. Mid-cavity obstructive HCM may be associated with a distal LV aneurysm and a worse prognosis. It is often not amenable to standard cardiac surgeryfor LV outflow obstruction. The long-term effects (mean follow-up 4.8+/-2.9 years) of dual chamber (DDD) pacemaker therapy in 14 patients with mid-cavity obstructive HCM (mean age 34+/-16 years, range 15-65 years) were studied. Patients were evaluated by cardiac catheterization at baseline and 6 months to 1 year after receiving DDD pacemakers off all drug therapy. Symptoms were improved in all patients and NYHA functional class reduced from 2.8+/-0.1 to 1.9+/-0.4 (P < 0.0005). Intracavitary LV pressure gradients was reduced significantly (43+/-36 vs 84+/-31 mmHg at baseline, P < 0.0005). There was a significant associated reduction in apical LV systolic pressure (152+/-37 vs 188+/-34 mmHg, P < 0.001). In addition, there was a trend towards increased exercise tolerance (445+/-123 vs 396+/-165). Cardiac output and LV filling pressures were unchanged. In conclusion, chronic DDD pacing results in significant symptomatic and hemodynamic improvement in this uncommon but important subset of patients with obstructive HCM in whom the role of cardiac surgery is less well defined compared with the more typical outflow tract location of LV obstruction.

R403Q and L908V mutant beta-cardiac myosin from patients with familial hypertrophic cardiomyopathy exhibit enhanced mechanical performance at the single molecule level

Familial hypertrophic cardiomyopathy (FHC) is a disease of the sarcomere. In the beta-myosin heavy chain gene, which codes for the mechanical enzyme myosin, greater than 40 point mutations have been found that are causal for this disease. We have studied the effect of two mutations, the R403Q and L908V, on myosin molecular mechanics. In the in vitro motility assay, the mutant myosins produced a 30% greater velocity of actin filament movement (v(actin)). At the single molecule level, v(actin) approximately d/t(on), where d is the myosin unitary step displacement and t(on) is the step duration. Laser trap studies were performed at 10 microM MgATP to estimate d and t(on) for the normal and mutant myosin molecules. The increase in v(actin) can be explained by a significant decrease in the average t(on)'s in both the R403Q and L908V mutants (approximately 30 ms) compared to controls (approximately 40 ms), while d was not different for all myosins tested (approximately 7 nm). Thus the mutations affect the kinetics of the cross-bridge cycle without any effect on myosin's inherent motion and force generating capacity. Based on these studies, the primary signal for the hypertrophic response appears to be an apparent gain in function of the individual mutant myosin molecules.

Identification of a gene responsible for familial Wolff-Parkinson-White syndrome

BACKGROUND

The Wolff-Parkinson-White syndrome, with a prevalence in Western countries of 1.5 to 3.1 per 1000 persons, causes considerable morbidity and may cause sudden death. We identified two families in which the Wolff-Parkinson-White syndrome segregated as an autosomal dominant disorder.

METHODS

We studied 70 members of the two families (57 in Family 1 and 13 in Family 2). The subjects underwent 12-lead electrocardiography and two-dimensional echocardiography. Genotyping mapped the gene responsible to 7q34-q36, a locus previously identified to be responsible for an inherited form of Wolff-Parkinson-White syndrome. Candidate genes were identified, sequenced, and analyzed in normal and affected family members to identify the disease-causing gene.

RESULTS

A total of 31 members (23 from Family 1 and 8 from Family 2) had the Wolff-Parkinson-White syndrome. Affected members of both families had ventricular preexcitation with conduction abnormalities and cardiac hypertrophy. The maximal combined two-point lod score was 9.82 at a distance of 5 cM from marker D7S636, which confirmed the linkage of the gene in both families to 7q34-q36. Haplotype analysis indicated that there were no alleles in common in the two families at this locus, suggesting that the two families do not have a common founder. We identified a missense mutation in the gene that encodes the gamma2 regulatory subunit of AMP-activated protein kinase (PRKAG2). The mutation results in the substitution of glutamine for arginine at residue 302 in the protein.

CONCLUSIONS

The identification of this genetic defect has important implications for elucidating the pathogenesis of ventricular preexcitation. Further understanding of how this molecular defect leads to supraventricular arrhythmias could influence the development of specific therapies for other forms of supraventricular arrhythmia.

Hypertrophic cardiomyopathy caused by a novel alpha-tropomyosin mutation (V95A) is associated with mild cardiac phenotype, abnormal calcium binding to troponin, abnormal myosin cycling, and poor prognosis

BACKGROUND

We report hypertrophic cardiomyopathy (HCM) in a Spanish-American family caused by a novel alpha-tropomyosin (TPM1) mutation and examine the pathogenesis of the clinical disease by characterizing functional defects in the purified mutant protein.

METHODS AND RESULTS

HCM was linked to the TPM1 gene (logarithm of the odds [LOD] score 3.17). Sequencing and restriction digestion analysis demonstrated a TPM1 mutation V95A that cosegregated with HCM. The mutation has been associated with 13 deaths in 26 affected members (11 sudden deaths and 2 related to heart failure), with a cumulative survival rate of 73+/-10% at the age of 40 years. Left ventricular wall thickness (mean 16+/-6 mm) and disease penetrance (53%) were similar to those for the ss-myosin mutations L908V and G256E previously associated with a benign prognosis. Left ventricular hypertrophy was milder than with the ss-myosin mutation R403Q, but the prognosis was similarly poor. With the use of recombinant tropomyosins, we identified several functional alterations at the protein level. The mutation caused a 40% to 50% increase in calcium affinity in regulated thin filament-myosin subfragment-1 (S1) MgATPase assays, a 20% decrease in MgATPase rates in the presence of saturating calcium, a 5% decrease in unloaded shortening velocity in in vitro motility assays, and no change in cooperative myosin S1 binding to regulated thin filaments.

CONCLUSIONS

In contrast to other reported TPM1 mutations, V95A-associated HCM exhibits unusual features of mild phenotype but poor prognosis. Both myosin cycling and calcium binding to troponin are abnormal in the presence of the mutant tropomyosin. The genetic diagnosis afforded by this mutation will be valuable in the management of HCM.

Myocardial bridging does not predict sudden death in children with hypertrophic cardiomyopathy but is associated with more severe cardiac disease

OBJECTIVES

We sought to examine the association between systolic compression of sections of epicardial coronary vessels (myocardial bridging) with myocardial perfusion abnormalities and clinical outcome in children with hypertrophic cardiomyopathy (HCM).

BACKGROUND

It has recently been suggested that myocardial bridging is an important cause of myocardial ischemia and sudden death in children with HCM.

METHODS

Angiograms from 57 children with HCM were reviewed for the presence of bridging (50% or more maximum systolic arterial compression). QT interval indices, echocardiographic and cardiac catheterization findings, treadmill exercise tests, exercise thallium scintigraphy, Holter monitoring and electrophysiologic study findings were compared in children with and without bridging. The findings were also related to the presence or absence of compression of septal branches of the left anterior descending artery (LAD).

RESULTS

Bridging was present in 23 (40%) of the children. Multiple coronary arteries were involved in four children. Bridging involved the LAD in 16 of 28 (57%) affected vessels. Myocardial perfusion abnormalities were present in 14 of 30 (47%) children without bridging and in 17 of 22 (94%) children with bridging, p = 0.002. However, bridging was associated with more severe septal hypertrophy (19+/-8 mm vs. 28+/-8 mm, p < 0.001), a higher septum:posterior wall thickness ratio (2.7+/-1.2 vs. 1.8+/-0.9, p < 0.001), and higher left ventricle (LV) outflow gradient (45+/-37 mm Hg vs. 16+/-28 mm Hg, p = 0.002). Compression of septal LAD branches was present in 37 (65%) of the children and was significantly associated with bridging, severity of LV hypertrophy and outflow obstruction. Multivariate analysis demonstrated that LV septal thickness and septal branch compression, and not bridging, were independent predictors of thallium perfusion abnormalities. There was a 90% power at 5% significance to detect an effect of bridging on thallium abnormalities at an odds ratio of 3. Bridging was also not associated with significantly greater symptoms, increased QT and QTc intervals and QTc dispersion, ventricular tachycardia on Holter or induced at EP study, or a worse prognosis.

CONCLUSIONS

Bridging and compression of septal branches of the LAD are common in HCM children and are related to magnitude of LV hypertrophy. Left ventricular hypertrophy and compression of intramyocardial branches of the epicardial coronary arteries may contribute to myocardial perfusion abnormalities. Our findings suggest that bridging does not result in myocardial ischemia and may not cause arrhythmias or sudden death in HCM children.

Inherited and de novo mutations in the cardiac actin gene cause hypertrophic cardiomyopathy

Mutations in genes encoding sarcomeric proteins cause hypertrophic cardiomyopathy (HCM). The sarcomeric protein actin plays a central, dual role in cardiac myocytes, generating contractile force by interacting with myosin and also transmitting force within and between cells. Two missense mutations in the cardiac actin gene (ACTC), postulated to impair force transmission, have been associated with familial dilated cardiomyopathy (DCM). Recently, a missense mutation in ACTC was found to cosegregate with familial HCM. To further test the hypothesis that mutations within functionally distinct domains of ACTC cause either DCM or HCM, we performed mutational analyses in 368 unrelated patients with familial or sporadic HCM. Single strand conformation polymorphism and sequence analyses of genomic DNA were performed. De novo mutations in ACTC were identified in two patients with sporadic HCM who presented with syncope in early childhood. Patients were heterozygous for missense mutations resulting in Pro164Ala and Ala331Pro amino acid substitutions, adjacent to regions of actin-actin and actin-myosin interaction, respectively. A mutation that cosegregated with familial HCM was also found, causing a Glu99Lys substitution in a weak actomyosin binding domain. The cardiac phenotype in many affected patients was characterized by an apical form of HCM. These findings support the hypothesis that a single amino acid substitution in actin causes either congestive heart failure or maladaptive cardiac hypertrophy, depending on its effect on actin structure and function.

Myocardial perfusion and sympathetic innervation in patients with hypertrophic cardiomyopathy

OBJECTIVES

This study assessed left ventricular myocardial perfusion and sympathetic innervation and function in hypertrophied and nonhypertrophied myocardial regions of patients with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Patients with HCM often have clinical findings consistent with increased cardiac sympathetic outflow. Little is known about the status of sympathetic innervation specifically in hypertrophic regions.

METHODS

We conducted positron emission tomographic (PET) scanning using the perfusion imaging agent 13N-ammonia (13NH3) and the sympathoneuronal imaging agent 6-[18F]-fluorodopamine (18F-FDA) in 8 patients with HCM and 15 normal volunteers. Positron emission tomographic data corrected for attenuation and the partial volume effect were analyzed using the region-of-interest technique.

RESULTS

Myocardial 13NH3-derived radioactivity was similar in hypertrophied and nonhypertrophied regions of patients with HCM and in normal volunteers. At all time points, the 18F:13N ratio was lower in hypertrophied than in nonhypertrophied regions of HCM patients and in the septum of normal volunteers (p = 0.001). Trends in 18F-FDA-derived radioactivity over time were normal in both hypertrophied and nonhypertrophied myocardium.

CONCLUSIONS

The results are consistent with decreased neuronal uptake of catecholamines in hypertrophied but not in nonhypertrophied myocardium of patients with HCM. Other aspects of cardiac sympathoneural function seem normal. Decreased neuronal uptake could reflect local relative hypoinnervation, decreased numbers of neuronal uptake sites, or metabolic limitations on cell membrane transport. By enhancing norepinephrine delivery to adrenoceptors for a given amount of sympathetic nerve traffic, decreased neuronal uptake can explain major clinical features of HCM.

Temporal repolarization lability in hypertrophic cardiomyopathy caused by beta-myosin heavy-chain gene mutations

BACKGROUND

Certain genetic mutations associated with hypertrophic cardiomyopathy (HCM) carry an increased risk of sudden death. QT variability identifies patients at a high risk for sudden death from ventricular arrhythmias. We tested whether patients with HCM caused by beta-myosin heavy-chain (beta-MHC) gene mutations exhibit labile ventricular repolarization using beat-to-beat QT variability analysis.

METHODS AND RESULTS

We measured the QT variability index and heart rate-QT interval coherence from Holter monitor recordings in 36 patients with HCM caused by known beta-MHC gene mutations and in 26 age- and sex-matched controls. There were 7 distinct beta-MHC gene mutations in these 36 patients; 9 patients had HCM caused by the malignant Arg(403)Gln mutation and 8 patients had HCM caused by the more benign Leu(908)Val mutation. The QT variability index was higher in HCM patients than in controls (-1.24+/-0.17 versus -1. 58+/-0.38, P<0.01), and the greatest abnormality was detected in patients with the Arg(403)Gln mutation (-0.99+/-0.49 versus -1. 46+/-0.43 in controls, P<0.05). In keeping with this finding, coherence was lower for the entire HCM group than for controls (P<0. 001). Coherence was also significantly lower in patients with the Arg(403)Gln mutation compared with controls (P<0.05).

CONCLUSIONS

These findings suggest that (1) patients with HCM caused by beta-MHC gene mutations exhibit labile repolarization quantified by QT variability analysis and, hence, may be more at risk for sudden death from ventricular arrhythmias, and (2) indices of QT variability may be particularly abnormal in patients with beta-MHC gene mutations that are associated with a poor prognosis.

Structural and functional responses of mammalian thick filaments to alterations in myosin regulatory light chains

The ordered array of myosin heads, characteristic of relaxed striated muscle thick filaments, is reversibly disordered by phosphorylating myosin regulatory light chains, decreasing temperature and/or ionic strength, increasing pH, and depleting nucleotide. In the case of light chain phosphorylation, disorder, most likely due to a change in charge affecting the light chain amino-terminus, reflects increased myosin head mobility, thus increased accessibility to actin, and results in increased calcium sensitivity of tension development. Thus, interactions between the unphosphorylated regulatory light chain and the filament backbone may help maintain the overall order of the relaxed filament. To define this relationship, we have examined the structural and functional effects of such manipulations as exchanging wild-type smooth and skeletal myosin light chains into permeabilized rabbit psoas fibers and removing regulatory light chains (without exchange) from such fibers. We have also compared the structural and functional parameters of biopsied fibers from patients with severe familial hypertrophic cardiomyopathy due to a single amino acid substitution in the regulatory light chains to those exhibited by fibers from normal relatives. Our results support a role for regulatory light chains in reversible ordering of myosin heads and suggest that economy of energy utilization may provide for evolutionary preservation of this function in vertebrate striated muscle.

The in vitro motility activity of beta-cardiac myosin depends on the nature of the beta-myosin heavy chain gene mutation in hypertrophic cardiomyopathy

Several mutations in the beta-myosin heavy chain gene cause hypertrophic cardiomyopathy. This study investigates (1) the in vitro velocities of translocation of fluorescently-labelled actin by beta-myosin purified from soleus muscle of 30 hypertrophic cardiomyopathy patients with seven distinct beta-myosin heavy chain gene mutations: Thr124Ile, Tyr162Cys, Gly256Glu, Arg403Gln, Val606Met, Arg870His, and Leu908Val mutations; and (2) motility activity of beta-myosin purified from cardiac and soleus muscle biopsies in the same patients. The velocity of translocation of actin by beta-myosin purified from soleus or cardiac muscle of 22 normal controls was 0.48 +/- 0.09 micron s-1. By comparison, the motility activity was reduced in all 30 patients with beta-myosin heavy chain gene mutations (range, 0.112 +/- 0.041 to 0.292 +/- 0.066 micron s-1. Notably, the Tyr162Cys and Arg403Gln mutations demonstrated significantly lower actin sliding velocities: 0.123 +/- 0.044, and 0.112 +/- 0.041 micron s-1, respectively. beta-myosin purified from soleus muscle from four patients with the Arg403Gln mutation had a similar actomyosin motility activity compared to beta-myosin purified from their cardiac biopsies (0.127 +/- 0.045 micron s-1 versus 0.119 +/- 0.068 micron s-1, respectively). Since these seven mutations lie in several distinct functional domains, it is likely that the mechanisms of their inhibitions of motility are different.

Hypertrophic cardiomyopathy: evaluation and treatment of patients at high risk for sudden death

Hypertrophic cardiomyopathy (HCM) is a heritable disease characterized by LV hypertrophy with markedly variable clinical, morphological, and genetic manifestations. It is the most common cause of sudden death in otherwise healthy young individuals. HCM patients often have disabling symptoms and are prone to arrhythmias. Frequently, there is associated LV systolic and diastolic dysfunction, LV outflow obstruction, and myocardial ischemia. Over the past decade, progress has been made in identifying patients who are at high risk for sudden death, in elucidating potential mechanisms of sudden death, and in defining therapeutic algorithms that may improve prognosis. It has also been possible to determine the genetic defect in some of the patients and to correlate clinical findings with the molecular defects. An exciting development has been the use of dual chamber pacemaker as an alternative to cardiac surgery to improve symptoms and relieve LV outflow obstruction.

Differential effects of changes in local myocardial refractoriness on atrial and ventricular latency

BACKGROUND

Assessment of myocardial refractoriness and conduction properties, critical to development and propagation of reentrant arrhythmias, is an integral part of the investigation of atrial and ventricular tachycardias through the use of programmed electrical stimulation. Local conduction itself, however, may be affected by myocardial refractoriness.

METHODS AND RESULTS

We studied the effects of changes in myocardial refractoriness on local conduction in right atrial and ventricular myocardium in 19 patients. Changes in effective, functional, and relative refractoriness were accomplished with the use of four pacing protocols, including drive train pacing cycle lengths (PCLs) of 600 and 400 milliseconds (ms) and drive train durations (DTDs) of 8 and 50 stimuli. Unipolar cathodal stimulation was performed from the distal electrode, and unipolar electrograms were recorded from the proximal three poles of quadripolar catheters with 5-mm interelectrode spaces. Atrial and ventricular effective and relative refractory periods (ERPs and RRPs) were significantly shortened by both the reduction in PCL and the increase in DTD. The reduction in the PCL shortened atrial and ventricular refractory periods significantly more than did the increase in the DTD. Changes in ventricular refractory periods were significantly greater compared with atrial refractory periods. The ratio of RRP to ERP was reduced in the atrium but significantly increased in the ventricle with reduction in PCL and increase in DTD. For all premature intervals, the conduction interval from stimulus to the first recording electrode pole was significantly greater than conduction intervals measured between subsequent electrode poles. The greatest increase in conduction interval with closely coupled premature complexes occurred between the stimulus artifact and the first recording electrode pole. Reduction in ventricular but not atrial ERP was associated with significantly increased local conduction interval.

CONCLUSIONS

First, most of the conduction delay after the stimulus artifact occurs within 5 mm from the pacing site. Second, closely coupled premature complexes delay conduction primarily by prolonging latency in the first 5 mm from the pacing site. Third, fundamental differences occur between the atrium and ventricle regarding changes in local conduction as a function of changes in ERP, suggesting that factors involved in sudden changes in refractoriness (eg, heart rate acceleration) could produce divergent effects on atrial and ventricular arrhythmogenesis.

A Fourier based algorithm for tracking SPAMM tags in gated magnetic resonance cardiac images

A method is described for automatically tracking spatial modulation of magnetization tag lines on gated cardiac images. The method differs from previously reported methods in that it uses Fourier based spatial frequency and phase information to separately track horizontal and vertical tag lines. Use of global information from the frequency spectrum of an entire set of tag lines was hypothesized to result in a robust algorithm with decreased sensitivity to noise. The method was validated in several ways: first, actual tagged cardiac images at end diastole were deformed known amounts, and the algorithm's predictions compared to the known deformations. Second, tagged, gated images of the thigh muscle (assumed to have similar signal to noise characteristics as cardiac images, but to not deform with time) were created. Again the algorithmic predictions could be compared to the known (zero magnitude) deformations and to thigh images which had been artificially deformed. Finally, actual cardiac tagged images were acquired, and comparisons made between manual, visual, determinations of tag line locations, and those predicted by the algorithm. At 0.5 T, the mean bias of the method was < 0.34 mm even at large deformations and at late (noisy) times. The standard deviation of the method, estimated from the tagged thigh images, was < 0.7 mm even at late times. The method may be expected to have even lower error at higher field strengths.

Mutations in either the essential or regulatory light chains of myosin are associated with a rare myopathy in human heart and skeletal muscle

The muscle myosins and hexomeric proteins consisting of two heavy chains and two pairs of light chains, the latter called essential (ELC) and regulatory (RLC). The light chains stabilize the long alpha helical neck of the myosin head. Their function in striated muscle, however, is only partially understood. We report here the identification of distinct missense mutations in a skeletal/ventricular ELC and RLC, each of which are associated with a rare variant of cardiac hypertrophy as well as abnormal skeletal muscle. We show that myosin containing the mutant ELC has abnormal function, map the mutant residues on the three-dimensional structure of myosin and suggest that the mutations disrupt the stretch activation response of the cardiac papillary muscles.

Relief of left ventricular outflow tract obstruction following inadvertent left ventricular apical pacing in a patient with hypertrophic cardiomyopathy

Dual chamber (DDD) pacing improves symptoms and relieves left ventricular (LV) outflow obstruction in hypertrophic cardiomyopathy. The ventricular lead is usually positioned at the right ventricular apex (RVA). We report a patient in whom the ventricular lead had inadvertently penetrated the septum, resulting in DDD pacing from the LV apex. However, after 3 months, obstruction was reduced and symptoms were improved. Pacing from LV apex and RVA resulted in comparable hemodynamic improvement. This case suggests that the asynchronous wave of septal contraction, originating from the apex, irrespective of ventricular site, accounts for the reduction in LV outflow obstruction.

Structural interpretation of the mutations in the beta-cardiac myosin that have been implicated in familial hypertrophic cardiomyopathy

In 10-30% of hypertrophic cardiomyopathy kindreds, the disease is caused by > 29 missense mutations in the cardiac beta-myosin heavy chain (MYH7) gene. The amino acid sequence similarity between chicken skeletal muscle and human beta-cardiac myosin and the three-dimensional structure of the chicken skeletal muscle myosin head have provided the opportunity to examine the structural consequences of these naturally occurring mutations in human beta-cardiac myosin. This study demonstrates that the mutations are related to distinct structural and functional domains. Twenty-four are clustered around four specific locations in the myosin head that are (i) associated with the actin binding interface, (ii) around the nucleotide binding site, (iii) adjacent to the region that connects the two reactive cysteine residues, and (iv) in close proximity to the interface of the heavy chain with the essential light chain. The remaining five mutations are in the myosin rod. The locations of these mutations provide insight into the way they impair the functioning of this molecular motor and also into the mechanism of energy transduction.

Abnormal contractile properties of muscle fibers expressing beta-myosin heavy chain gene mutations in patients with hypertrophic cardiomyopathy

Missense mutations in the beta-myosin heavy chain (beta-MHC) gene cause hypertrophic cardiomyopathy (HCM). As normal and mutant beta-MHCs are expressed in slow-twitch skeletal muscle of HCM patients, we compared the contractile properties of single slow-twitch muscle fibers from patients with three distinct beta-MHC gene mutations and normal controls. Fibers with the 741Gly-->Arg mutation (near the binding site of essential light chain) demonstrated decreased maximum velocity of shortening (39% of normal) and decreased isometric force generation (42% of normal). Fibers with the 403Arg-->Gln mutation (at the actin interface of myosin) showed lowered force/stiffness ratio (56% of normal) and depressed velocity of shortening (50% of normal). Both the 741Gly-->Arg and 403Arg-->Gln mutation-containing fibers displayed abnormal force-velocity relationships and reduced power output. Fibers with the 256Gly-->Glu mutation (end of ATP-binding pocket) had contractile properties that were indistinguishable from normal. Thus there is variability in the nature and extent of functional impairments in skeletal fibers containing different beta-MHC gene mutations, which may correlate with the severity and penetrance of the disease that results from each mutation. These functional alterations likely constitute the primary stimulus for the cardiac hypertrophy that is characteristic of this disease.

Identification of patients with hypertrophic cardiomyopathy at high risk for sudden death

Patients with hypertrophic cardiomyopathy are at increased risk for sudden death. Recent studies have improved our ability to risk-stratify such patients and have elucidated several potential mechanisms of sudden death and syncope. Certain noninvasive tests, such as signal-averaged electrocardiography and measurements of cardiac autonomic function and QT/QT dispersion, are often abnormal in hypertrophic cardiomyopathy, but are not useful for risk stratification. Myocardial ischemia determined by exercise thallium scintigraphy, however, identifies young patients with hypertrophic cardiomyopathy who are at high risk for cardiac arrest and syncope. Nonsustained ventricular tachycardia on ambulatory Holter monitoring in the absence of symptoms of impaired consciousness is associated with a benign prognosis and is not predictive of sudden death. Conversely, ventricular tachycardia induced at electrophysiologic study identifies adult patients with hypertrophic cardiomyopathy who subsequently experience sudden death. Finally, characterization of the natural history of the genetic defects will increasingly become an integral part of risk evaluation in hypertrophic cardiomyopathy.

Long-term results of dual-chamber (DDD) pacing in obstructive hypertrophic cardiomyopathy. Evidence for progressive symptomatic and hemodynamic improvement and reduction of left ventricular hypertrophy

BACKGROUND

We previously reported that 6 to 12 weeks of dual-chamber (DDD) pacing results in clinical and hemodynamic improvement in obstructive hypertrophic cardiomyopathy (HCM). This study examines the long-term results of DDD pacing in obstructive HCM.

METHODS AND RESULTS

DDD devices were implanted in 84 patients (mean age, 49 +/- 16 years) with obstructive HCM and severe drug-refractory symptoms. At a mean follow-up of 2.3 +/- 0.8 years (maximum, 3.5 years), the New York Heart Association (NYHA) functional class had improved significantly (1.6 +/- 0.6 versus 3.2 +/- 0.5, P < .00001). Symptoms were eliminated in 28 patients (33%), improved in 47 patients (56%), but remained unchanged in 7 patients (8%). Two patients died suddenly (97% cumulative 3-year survival rate). In 74 patients with significant left ventricular outflow tract (LVOT) obstruction at rest, the LVOT gradients were significantly reduced at follow-up (27 +/- 31 versus 96 +/- 41 mm Hg, P < .00001). Symptoms and provokable LVOT gradients were also reduced in all 10 patients without significant resting but with provokable LVOT obstruction. Persistence of the LVOT obstruction and symptoms was attributed to inability to pre-excite the interventricular septum (n = 8) and onset of atrial fibrillation (n = 7). Fifty patients had two cardiac catheterization evaluations, 3 +/- 1 and 16 +/- 4 months after implantation of a pacemaker. In this subgroup, the NYHA functional class improved from 3.2 +/- 0.5 at baseline to 1.8 +/- 0.7 at the initial evaluation (P < .00001), but with a further significant improvement at the second evaluation: 1.4 +/- 0.6, P < .001. This symptomatic improvement was associated with progressive reduction of LVOT gradient at the two evaluations: baseline, 100 +/- 47 mm Hg; first evaluation, 41 +/- 36 mm Hg (P < .0001); and second evaluation, 29 +/- 34 mm Hg (P < .01). Despite the presence of left bundle branch block, DDD pacing reduced LVOT obstruction significantly in 15 patients (LVOT gradient, baseline 89 +/- 36 mm Hg versus 18 +/- 26 mm Hg at follow-up, P < .0001). There was a weak but significant correlation between the reduction in LVOT gradients accomplished by AV pacing before implantation of DDD device and the eventual reduction in LVOT gradients recorded at the follow-up evaluation (r = .38, P = .0017). Echocardiography demonstrated significant thinning of the anterior septum and distal anterior LV wall in the absence of deterioration of LV systolic function.

CONCLUSIONS

(1) Although most of the improvement of symptoms and hemodynamic indexes occurs during the first few months of DDD pacing, further changes are often observed a year later; (2) DDD pacing is associated with an excellent prognosis in a subgroup of severely disabled patients, many of whom present with syncope or presyncope; (3) baseline pacing studies are not essential to identify patients who may benefit from pacing; (4) preexisting left bundle branch block is compatible with severe LVOT obstruction, and DDD pacing is also beneficial in this subgroup; (5) DDD pacing reduces both resting and provokable LVOT obstruction; (6) additional therapy, for example, radiofrequency ablation of the AV node, may be necessary in some patients either to preexcite the interventricular septum or to control atrial fibrillation; and (7) although LV hypertrophy has been considered a primary feature of HCM, pacing appears to reverse LV wall thickness in a significant subset of adult HCM patients.

Results of permanent dual-chamber pacing in symptomatic nonobstructive hypertrophic cardiomyopathy

Because dual-chamber (DDD) pacing has been shown to be of benefit regarding symptoms, rest and pacing hemodynamics, and exercise duration in patients with obstructive hypertrophic cardiomyopathy (HC), the effect of DDD pacing was assessed in patients with nonobstructive HC who were significantly symptomatic despite medical management. Echocardiography, treadmill exercise testing, thallium-201 scintigraphy, radionuclide angiography, and invasive measurement of rest and semi-erect bicycle exercise hemodynamics were performed in 12 patients before and approximately 4 months after permanent DDD pacing. One patient died 3 months after pacemaker implantation, because of worsening diastolic heart failure. Of the remaining 11 patients, 10 improved regarding symptoms, and treadmill exercise duration was longer during DDD pacing than during the baseline study in sinus rhythm (6.8 +/- 2.8 to 8.5 +/- 2.8 minutes; p < 0.01), with a significant increase in the peak double product achieved (28.9 +/- 6.1 to 31.0 +/- 6.8 x 10(3); p < 0.05). However, there were significant reductions in cardiac (3.7 +/- 0.9 to 3.1 +/- 0.5 ml/min/m2; p < 0.01) and stroke volume (47.4 +/- 11.4 to 38.7 +/- 6.5 ml/beat/m2; p < 0.01) indexes, and a trend toward reduction in submaximal stroke volume index during DDD pacing as compared with the baseline study in sinus rhythm (44.7 +/- 13.5 to 40.9 +/- 10.9 ml/beat/m2; p = 0.097). No change in peak heart rate, cardiac or stroke volume index, mean blood pressure, or pulmonary artery or pulmonary capillary wedge pressure occurred with peak exercise during DDD pacing as compared with the initial exercise study in sinus rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)

Genotype-phenotype correlations in hypertrophic cardiomyopathy. Insights provided by comparisons of kindreds with distinct and identical beta-myosin heavy chain gene mutations

BACKGROUND

We have previously described two distinct mutations in the beta-myosin heavy chain gene with markedly different clinical presentations and outcome: The 908Leu-->Val mutation was associated with a low disease penetrance and a benign prognosis. In contrast, the 403Arg-->Gln mutation in a Caucasian kindred was associated with a 100% disease penetrance and high incidence of sudden cardiac death. Recently, another mutation, 606Val-->Met, has been reported to be associated with "near normal survival" and offered as evidence for the benign nature of neutral charge substitutions.

METHODS AND RESULTS

We report (1) a large kindred (245 family members at risk of inheriting the disease gene) with a 256Gly-->Glu mutation characterized by a similar disease penetrance in adults and in children (56% and 60%, respectively) and a cumulative sudden cardiac death rate of only 2% at 50 years of age, (2) a kindred with the 606Val-->Met mutation with four sudden cardiac deaths in eight affected individuals, and (3) a Korean kindred with the 403Arg-->Gln mutation. Although the disease occurred early and was associated with a high prevalence of myocardial ischemia in both of our kindreds with the 403Arg-->Gln mutation, no sudden cardiac death or syncope has occurred in the Korean kindred. Furthermore, in the Caucasian kindred, all patients had nonobstructive hypertrophic cardiomyopathy, but most of the patients in the Korean kindred had left ventricular outflow obstruction.

CONCLUSIONS

The conclusions are as follows: (1) Although several sudden cardiac deaths are sufficient to establish that a mutation is malignant, study of a large kindred is necessary to be certain that a mutation is benign. To date, only the 908Leu-->Val and the 256Gly-->Glu mutations satisfy this requirement. (2) The 256Gly-->Glu mutation demonstrates that not all mutations that result in a charge change are malignant. (3) Conversely, the 606Val-->Met mutation is malignant in some kindreds; hence, despite the absence of a charge change, minor substitutions in critical regions of beta-myosin heavy chain protein may also have serious consequences. (4) The diverse ethnic origins of the two 403Arg-->Gln kindreds provide evidence suggesting that the identical mutation occurred independently and was associated with different genetic backgrounds. Their distinct phenotypes underline the importance of modifying genes and nongenetic factors.

Radiofrequency catheter atrioventricular node ablation in patients with permanent cardiac pacing systems

Following successful RF ablation of the atrioventricular node (AVN), temporary pacing is necessary prior to insertion of a permanent pacemaker. The risks and inconvenience of temporary pacing could be avoided if a permanent pacemaker is already in place. This study reports the feasibility of RF ablation of the AVN in 27 patients (age 55 +/- 17 years, 15 males) with hypertrophic cardiomyopathy and pacemakers. Indications for AVN ablation were drug refractory atrial fibrillation in 24 patients, and rapid AVN conduction preventing septal pre-excitation by DDD pacemaker, inserted for relief of left ventricular outflow obstruction, in three cases. Sixteen patients had DDD devices and 11 patients had VVI devices. During RF ablation, each pacemaker was programmed to VVI at 50 beats/min. The ablation catheter was manipulated with fluoroscopic control to avoid close contact with or disturbance of the pacing leads. In 16 patients, RF ablation was performed immediately following pacemaker implantation but in the remaining patients, the AVN was ablated 6-32 months after pacemaker implantation. The power applied was 25-50 watts for a duration of 15-60 seconds. AV block was achieved in all cases but required 34 +/- 36 applications for 16.5 +/- 17.8 min/case. RF ablation consistently caused reversion to magnet rate in one patient and temporarily inhibited appropriate pacemaker discharge in another. However, no other pacemaker or lead malfunction was detected so that temporary pacing was not required in any case. At 6 +/- 3 months follow-up, all pacemakers were functioning normally without alteration in pacing parameters from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial ischemia detected by thallium scintigraphy is frequently related to cardiac arrest and syncope in young patients with hypertrophic cardiomyopathy

OBJECTIVES

The purpose of this study was to determine the frequency of myocardial ischemia as a potential mechanism for cardiac arrest and syncope in young patients with hypertrophic cardiomyopathy who experienced such complications.

BACKGROUND

Sudden cardiac death and syncope occur frequently in patients with hypertrophic cardiomyopathy. Although ventricular arrhythmias account for most of these events in adult patients, the mechanism responsible for cardiac arrest and syncope in young patients has not been established.

METHODS

Twenty-three patients with hypertrophic cardiomyopathy, aged 6 to 23 years, with previous cardiac arrest (n = 8), syncope (n = 7) or a family history of sudden cardiac death (n = 8) were evaluated to determine the prevalence of spontaneous ambulatory ventricular tachycardia (24- to 72-h electrocardiographic [ECG] monitoring), exercise-induced myocardial ischemia (thallium scintigraphy) and inducibility of ventricular tachycardia (electrophysiologic studies).

RESULTS

Three of 15 patients with a history of cardiac arrest or syncope had ventricular tachycardia on ambulatory ECG monitoring. However, all 15 patients, had inducible ischemia by thallium scintigraphy compared with only 3 (37%) of 8 patients with no such history (p < 0.01). In contrast, ventricular tachycardia induction was uncommon in all of the young patients (27% in those with cardiac arrest or syncope; 0% in the others). During therapy for ischemia with verapamil alone or in combination with beta-adrenergic blocking agents, only 4 of the 15 patients with cardiac arrest or syncope had further episodes. In three of the four patients, these events were temporally related to discontinuation of verapamil. Among eight patients who had a repeat exercise thallium study while receiving anti-ischemic therapy, seven (88%) had improved regional thallium uptake, of whom three had normal thallium studies.

CONCLUSIONS

These data suggest that in young patients with hypertrophic cardiomyopathy, sudden cardiac arrest or syncope is frequently related to ischemia rather than to a primary arrhythmogenic ventricular substrate.

Skeletal muscle expression and abnormal function of beta-myosin in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is an important inherited disease. The phenotype has been linked, in some kindreds, to the beta-myosin heavy chain (beta-MHC) gene. Missense and silent mutations in the beta-MHC gene were used as markers to demonstrate the expression of mutant and normal cardiac beta-MHC gene message in skeletal muscle of hypertrophic cardiomyopathy patients. Mutant beta-myosin, also shown to be present in skeletal muscle by Western blot analysis, translocated actin filaments slower than normal controls in an in vitro motility assay. Thus, single amino acid changes in beta-myosin result in abnormal actomyosin interactions, confirming the primary role of missense mutations in beta-MHC gene in the etiology of hypertrophic cardiomyopathy.

Missense mutations in the beta-myosin heavy-chain gene cause central core disease in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an important cause of sudden death in apparently healthy young individuals. In less than half of kindreds with HCM, the disease is linked to the beta-myosin heavy-chain gene locus (MYH7). We have recently described two missense MYH7 gene mutations [Arg-403 to Gln (R403Q) and Leu-908 to Val (L908V)] and found that the mutant message is present in skeletal muscle soleus) and that the mutant beta-myosin obtained from soleus muscle has abnormal in vitro motility activity. Having identified a second kindred with the R403Q mutation, and 3 other kindreds with two additional mutations (G741R and G256E), we performed histochemical analysis of soleus muscle biopsies from 25 HCM patients with one of these four mutations. Light microscopic examination of the NADH-stained biopsies revealed the presence of central core disease (CCD) of skeletal muscle, a rare autosomal dominant nonprogressive myopathy characterized by a predominance of type I "slow" fibers and an absence of mitochondria in the center of many type I fibers. CCD was present in 10 of 13 patients with the L908V mutation, 5 of 8 patients with the R403Q mutation, 1 of 3 patients with the G741R mutation, and 1 patient with the G256E mutation. Mild-to-moderate myopathic changes with muscle fiber hypertrophy were present in 16 patients. Notably, CCD was present in 2 adults and 3 children with the L908V mutation who did not have cardiac hypertrophy. In contrast, soleus muscle samples from 5 patients from 4 kindreds in which HCM was not linked to the MYH7 locus showed no myopathy or CCD. Soleus muscle biopsies from 5 control subjects also showed normal histology. This work demonstrates that (i) MYH7-associated HCM is often a disease of striated muscle but with predominant cardiac involvement and (ii) a subset of HCM patients with MYH7 gene missense mutations have CCD.

Suppression of incessant ventricular tachycardia in hypertrophic cardiomyopathy associated with improvement of severe left ventricular dysfunction

A 32-year-old black man presented with a history of palpitations since childhood and two syncopal episodes. He was found to have incessant ventricular tachycardia, impaired left ventricular contraction (ejection fraction 9%), and nonobstructive hypertrophic cardiomyopathy. Procainamide abolished the arrhythmia and the ejection fraction rose to 22% in sinus rhythm. Later treatment was switched to amiodarone, which suppressed the ventricular tachycardia but necessitated pacemaker implantation. He has remained well during the subsequent 2 years. Left ventricular ejection fraction has increased to 47% measured in paced rhythm. The improvement in left ventricular function has been attributed to suppression of the incessant ventricular tachycardia.

Prognostic determinants in hypertrophic cardiomyopathy. Prospective evaluation of a therapeutic strategy based on clinical, Holter, hemodynamic, and electrophysiological findings

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) frequently have arrhythmias and hemodynamic abnormalities and are prone to sudden death and syncope. An important need exists for improved risk stratification and definition of appropriate investigation and therapy.

METHODS AND RESULTS

The relation of 31 clinical, Holter, cardiac catheterization, and electrophysiological (EP) variables to subsequent cardiac events in 230 HCM patients was examined by multivariate analysis. Studies were for cardiac arrest (n = 32), syncope (n = 80), presyncope (n = 52), ventricular tachycardia (VT) on Holter (n = 36), a strong family history of sudden death (n = 9), and palpitations (n = 21). Nonsustained VT on Holter was present in 115 patients (50%). Sustained ventricular arrhythmia was induced in 82 patients (36%). Seventeen cardiac events (eight sudden deaths, one cardiac arrest, and eight syncope with defibrillator discharges) occurred during a follow-up of 28 +/- 19 months. The 1-year and 5-year event-free rates were 99% and 79%, respectively. Two variables were significant independent predictors of subsequent events: sustained ventricular arrhythmia induced at EP study (beta, 3.5; p = 0.002) and a history of cardiac arrest or syncope (beta, 2.9; p less than 0.05). Only two of 66 patients without symptoms of impaired consciousness had a cardiac event (3-year event-free rate, 97%). In contrast, nonsustained VT on Holter was associated with a worse prognosis only in patients with symptoms of impaired consciousness: 11 of 79 symptomatic patients with VT on Holter (14%) had events versus only four of 85 symptomatic patients without VT on Holter (5%) (p = 0.057). Notably, none of 51 patients without symptoms of impaired consciousness in whom VT was not induced at EP study had a cardiac event.

CONCLUSIONS

In HCM, VT on Holter is of benign prognostic significance in the absence of symptoms of impaired consciousness and inducible VT, and sustained VT induced at EP study, especially when associated with cardiac arrest or syncope, identifies a subgroup at high risk for subsequent cardiac events.

Altered cardiac hemodynamic and electrical state in normal sinus rhythm after chronic dual-chamber pacing for relief of left ventricular outflow obstruction in hypertrophic cardiomyopathy

Dual-chamber (DDD) pacing relieves left ventricular (LV) outflow tract obstruction in patients with hypertrophic cardiomyopathy. The reduction in LV outflow gradient persists in some patients after cessation of pacing. Twelve-lead and signal-averaged electrocardiograms were obtained before and after 12 weeks of DDD pacing in 18 patients with obstructive hypertrophic cardiomyopathy to determine whether the altered hemodynamic state after chronic pacing is accompanied by electrical changes. Hemodynamic studies were performed at baseline and at follow-up. Signal-averaged electro-cardiograms were obtained using a Corazonix Predictor and bidirectional filters at 25 Hz to a noise level of less than 0.5 microV. At follow-up, LV outflow tract gradients were reduced significantly during DDD pacing and with cessation of pacing in sinus rhythm by 56 +/- 10 and 47 +/- 10 mm Hg, respectively (p less than 0.001). There was no simple relation between changes in LV outflow tract gradient and in the electrocardiogram. For example, amplitude of the R wave in V5,6 was reduced by greater than or equal to 0.5 mv in 4 patients, unchanged in 12 and increased in 2. Similarly, the S wave in leads V1,2 was reduced in 7 patients, unchanged in 7 and increased in 4. The T wave became more negative (greater than or equal to 0.1 mv) in leads II, III, aVF and V5,6 in 13 patients and more positive in leads I and aVL in 12.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in clinical expression of hypertrophic cardiomyopathy associated with two distinct mutations in the beta-myosin heavy chain gene. A 908Leu----Val mutation and a 403Arg----Gln mutation

BACKGROUND

The disease gene for hypertrophic cardiomyopathy (HCM) has been identified as the beta-myosin heavy chain (beta-MHC) gene in some HCM families. We describe extensive clinical evaluations in two kindreds with two distinct point mutations in the beta-MHC gene.

METHODS AND RESULTS

We used single-strand confirmation polymorphism (SSCP) gel analysis of polymerase chain reaction-amplified products capturing each of the 40 beta-MHC gene exons to identify distinct missense mutations in two HCM kindreds. Clinical, ECG, and echocardiographic studies were performed in the two kindreds: kindred 2755 with amino acid 908Leu----Val mutation and kindred 2002 with amino acid 403Arg----Gln mutation. The morphological appearances of HCM were similar in these two kindreds. However, the two kindreds differed with respect to disease penetrance, age of onset of disease, and incidence of premature sudden death. Twelve of 31 adults (greater than or equal to 17 years) with the disease gene in kindred 2755 did not have left ventricular hypertrophy (LVH), and only five of these had ECG abnormalities. Thus, the disease penetrance in adults with this mutation was only 61%. None of 11 children aged less than 16 years had LVH. The 908 mutation was associated with a low incidence of cardiac events: Only two sudden deaths and one syncope occurred in 46 individuals with the mutant allele. In contrast, LVH was present in all 11 adults in kindred 2002 with the 403 mutation (100% disease penetrance). In addition, three of four affected children were symptomatic and had clinical evidence of HCM. The disease in this kindred was severe and resulted in six premature sudden deaths. Seven additional patients had syncope or presyncope.

CONCLUSIONS

In some kindreds, the HCM disease gene is more prevalent than indicated by echocardiography and ECG. Some point mutations may be associated with a more malignant prognosis. Preclinical identification of children with mutations associated with a high incidence of sudden death and syncope provides the opportunity to evaluate efficacy of early therapeutic interventions.

Impact of dual-chamber permanent pacing in patients with obstructive hypertrophic cardiomyopathy with symptoms refractory to verapamil and beta-adrenergic blocker therapy

BACKGROUND

Patients with obstructive hypertrophic cardiomyopathy (HCM) with symptoms refractory to drugs (beta-blockers or verapamil) are candidates for cardiac surgery (left ventricular septal myectomy or mitral valve replacement). The present study examines prospectively the ability of dual-chamber (DDD) pacing to improve symptoms and relieve left ventricular outflow obstruction in such patients.

METHODS AND RESULTS

Forty-four consecutive patients with obstructive HCM who had failed to benefit from pharmacotherapy underwent treadmill exercise tests, echocardiography, and cardiac catheterization before and 1.5-3 months after implantation of a DDD pacemaker. Symptoms (angina, dyspnea, palpitations, presyncope, and syncope), New York Heart Association functional class status (1.7 +/- 0.7 versus 3.4 +/- 0.5, p less than 0.00001), and exercise durations were improved at follow-up evaluation. This was associated with significant reduction in left ventricular outflow tract gradient (38 +/- 38 versus 87 +/- 43 mm Hg, p less than 0.0001) and significant increases in cardiac output and systemic arterial pressures. Notably, when pacing was discontinued and comparisons were made in sinus rhythm, treadmill exercise durations were greater and left ventricular outflow tract gradients were less at the follow-up evaluation compared with the baseline study.

CONCLUSIONS

DDD pacing is an effective alternative to surgery in most patients with obstructive HCM with drug-refractory symptoms. The beneficial effects of pacing continue to be evident when pacing is acutely discontinued.

Impact of surgical relief of outflow obstruction on thallium perfusion abnormalities in hypertrophic cardiomyopathy

BACKGROUND

To assess the impact of surgical relief of left ventricular outflow obstruction on myocardial perfusion abnormalities in patients with obstructive hypertrophic cardiomyopathy, 20 symptomatic patients who underwent a septal myectomy or mitral valve replacement were studied with assessment of myocardial perfusion during exercise by 201Tl emission computed tomography before and 6 months after surgery.

METHODS AND RESULTS

Before surgery, 15 patients had myocardial perfusion defects during exercise that completely normalized at rest, one patient had both reversible and fixed perfusion defects, two patients had fixed defects only, and two patients had normal exercise and rest thallium scans. After surgical relief of left ventricular outflow obstruction (basal gradient reduced from 62 +/- 40 to 7 +/- 12 mm Hg, p less than 0.001; peak provokable gradient reduced from 131 +/- 27 to 49 +/- 36 mm Hg, p less than 0.001), repeat exercise thallium studies showed complete normalization of perfusion defects in 11 patients, including the two patients with fixed defects alone before surgery, and improvement in the magnitude and distribution of perfusion defects in five additional patients. This was associated with a significant reduction in the number of patients with reversible regional defects (five patients compared with 13 patients before surgery, p = 0.026) and of patients with endocardial hypoperfusion (four patients compared with 12 patients before surgery, p = 0.024). Furthermore, increased lung uptake of thallium was noted in five patients after surgery, compared with 12 patients before surgery (p = 0.055). Only two patients with reversible perfusion defects before surgery had unchanged postoperative studies. However, four patients acquired new fixed defects as a consequence of surgery, and two of these four had the greatest severity and distribution of left ventricular hypertrophy by echocardiography. These four patients experienced a substantially greater decrease in ejection fraction (-26 +/- 15%) after surgery than the remaining patients (-3 +/- 14%, p less than 0.01).

CONCLUSIONS

Surgical relief of left ventricular outflow obstruction results in normalization or improvement of myocardial perfusion in the majority of patients with reversible and fixed perfusion defects by 201Tl scintigraphy. However, surgery may result in myocardial injury and scarring, with consequent decreased left ventricular ejection fraction in some patients.

Evidence of genetic heterogeneity in five kindreds with familial hypertrophic cardiomyopathy

BACKGROUND

Recently, two families with hypertrophic cardiomyopathy have been shown to have mutations in the cardiac beta-myosin heavy chain gene (beta-MHC) located on the long arm of chromosome 14.

METHODS AND RESULTS

We have performed linkage analysis of five newly ascertained pedigrees with more than 50 chromosomal markers detecting polymorphisms. Our findings confirm the linkage to beta-MHC gene locus on chromosome 14 in one family (LOD score, 4.50) and suggest linkage to the same gene in another kindred. Chromosome 14 markers were not linked to the disease gene in the other three kindreds, however, and a test for genetic heterogeneity was statistically significant. Moreover, markers for the beta-MHC gene identified affected individuals who were recombinants with respect to this gene and the disease phenotype in these three kindreds.

CONCLUSIONS

These results provide conclusive evidence that hypertrophic cardiomyopathy in separate families is caused by mutations in disease genes at two or more locations in the genome.

Utility of continuous wave Doppler echocardiography in the noninvasive assessment of left ventricular outflow tract pressure gradient in patients with hypertrophic cardiomyopathy

Subaortic obstruction is an important determinant of the clinical presentation of and therapeutic approach to patients with hypertrophic cardiomyopathy. Therefore, assessment of the presence and magnitude of the intraventricular pressure gradient is paramount in the clinical evaluation of these patients. To establish the utility of continuous wave Doppler echocardiography in assessing the pressure gradient in hypertrophic cardiomyopathy, 28 patients representing the wide hemodynamic spectrum of this disease underwent simultaneous determination of the subaortic gradient by continuous wave Doppler ultrasound and cardiac catheterization. With use of the modified Bernoulli equation, the Doppler-estimated gradient showed a strong correlation with the maximal instantaneous pressure difference measured at catheterization, both under basal conditions (r = 0.93; p less than 0.0001) and during provocative maneuvers (r = 0.89; p less than 0.0001). In 26 of the 28 patients, all assessments of the subaortic gradient were in agreement within 15 mm Hg (average difference 5 +/- 3 mm Hg). In the other two patients there were substantial differences between these measurements (under basal conditions in one patient and after provocation in another), although the Doppler technique predicted the presence of marked subaortic obstruction in each. In both patients the erroneous interpretation was due to superimposition of the mitral regurgitation signal on that of left ventricular outflow. Doppler waveforms from the left ventricular outflow tract showed variability in contour among different patients and in individual patients. Hence, continuous wave Doppler echocardiography is a useful noninvasive method for estimating the subaortic gradient in patients with hypertrophic cardiomyopathy. However, technical factors such as contamination of the outflow tract jet with that of mitral regurgitation and variability in waveform configuration may importantly influence such assessments of the subaortic gradient.

Sudden cardiac death in hypertrophic cardiomyopathy

Sudden death is an important facet of the natural history of hypertrophic cardiomyopathy. Issues related to the nature and etiology of sudden death and the prospective identification of those patients at increased risk have been the subject of intense study, and consequently, our concepts and knowledge have continued to evolve. Occurrence of sudden death has been reported to be about 2-3% per year in a hospital-based referral population and, although described in most age groups, is most common in older children and young adults. The typical profile is that of a young asymptomatic patient with substantially increased left ventricular wall thickness who dies while performing sedentary or modest physical activities; however, a substantial minority die suddenly during or just after severe exertion, including those participating in competitive athletics. Other risk factors that have been identified in patients with hypertrophic cardiomyopathy include nonsustained ventricular tachycardia on ambulatory electrocardiogram, a strong family history of sudden death, and prior occurrence of syncope (or cardiac arrest). Electrophysiological studies have shown that most patients judged at increased risk for sudden death have sinoatrial or His-Purkinje conduction disease or inducible supraventricular or ventricular tachycardia; inducibility of a sustained ventricular arrhythmia is associated with prior occurrence of syncope or cardiac arrest. Hemodynamic and electrophysiological studies in patients with hypertrophic cardiomyopathy have demonstrated several potential mechanisms for cardiac arrest or sudden death, including atrial arrhythmias associated with hypotension, bradyarrhythmias, and ventricular tachyarrhythmias, all of which can be exacerbated in the presence of left ventricular outflow tract obstruction or myocardial ischemia.

Myocardial metabolic, hemodynamic, and electrocardiographic significance of reversible thallium-201 abnormalities in hypertrophic cardiomyopathy

BACKGROUND

Exercise-induced abnormalities during thallium-201 scintigraphy that normalize at rest frequently occur in patients with hypertrophic cardiomyopathy. However, it is not known whether these abnormalities are indicative of myocardial ischemia.

METHODS AND RESULTS

Fifty patients with hypertrophic cardiomyopathy underwent exercise 201Tl scintigraphy and, during the same week, measurement of myocardial lactate metabolism and hemodynamics during pacing stress. Thirty-seven patients (74%) had one or more 201Tl abnormalities that completely normalized after 3 hours of rest; 26 had regional myocardial 201Tl defects, and 26 had apparent left ventricular cavity dilatation with exercise, with 15 having coexistence of these abnormal findings. Of the 37 patients with reversible 201Tl abnormalities, 27 (73%) had metabolic evidence of myocardial ischemia during rapid atrial pacing (myocardial lactate extraction of 0 mmol/l or less) compared with four of 13 patients (31%) with normal 201Tl scans (p less than 0.01). Eleven patients had apparent cavity dilatation as their only 201Tl abnormality; their mean postpacing left ventricular end-diastolic pressure was significantly higher than that of the 13 patients with normal 201Tl studies (33 +/- 5 versus 21 +/- 10 mm Hg, p less than 0.001). There was no correlation between the angiographic presence of systolic septal or epicardial coronary arterial compression and the presence or distribution of 201Tl abnormalities. Patients with ischemic ST segment responses to exercise had an 80% prevalence rate of reversible 201Tl abnormalities and a 70% prevalence rate of pacing-induced ischemia. However, 69% of patients with nonischemic ST segment responses had reversible 201Tl abnormalities, and 55% had pacing-induced ischemia.

CONCLUSIONS

Reversible 201Tl abnormalities during exercise stress are markers of myocardial ischemia in hypertrophic cardiomyopathy and most likely identify relatively underperfused myocardium. In contrast, ST segment changes with exercise and systolic compression of coronary arteries on angiography are unreliable markers of inducible myocardial ischemia in hypertrophic cardiomyopathy. Apparent cavity dilatation during 201Tl scintigraphy may indicate ischemia-related changes in left ventricular filling, with elevation in diastolic pressures and endocardial compression.

Value of electrophysiologic studies in hypertrophic cardiomyopathy treated with amiodarone

The relation of electrophysiologic effects of amiodarone to long-term outcome was studied in 35 patients with hypertrophic cardiomyopathy (HC). Indications for electrophysiologic studies were: cardiac arrest (n = 3), syncope/presyncope (n = 27) and asymptomatic ventricular tachycardia (VT) (n = 5). Twenty-eight patients (80%) had VT, 3 (9%) atrial tachycardia and 3 (9%) paroxysmal atrial fibrillation during 24-hour Holter monitoring. The studies were repeated after a total amiodarone dose of 58 +/- 122 g and during a maintenance median daily dose of 400 mg. Amiodarone abolished paroxysmal atrial arrhythmias in all 6 patients. However, it caused marked atrioventricular nodal conduction abnormality in 3 patients and heart block or marked HV interval prolongation (to greater than or equal to 100 ms) in 4 patients. Sustained VT was induced in 26 patients (74%) at baseline study and in 23 patients (66%) taking amiodarone therapy. With amiodarone, VT was no longer inducible or was more difficult to induce in 11 patients (31%), and the drug abolished VT during Holter monitoring in all patients. However, VT was easier to induce with amiodarone or was induced only with amiodarone in 18 (51%) patients. Amiodarone significantly slowed the rate of induced VT (from 248 +/- 29 to 214 +/- 37 beats/min, p less than 0.001). This was associated with a change in its morphology from polymorphic to monomorphic VT in 7 patients. During a follow up of 18 +/- 14 months (range 2 to 56), amiodarone was discontinued because of adverse effects in 8 patients (23%).(ABSTRACT TRUNCATED AT 250 WORDS)

Sudden death during empiric amiodarone therapy in symptomatic hypertrophic cardiomyopathy

Amiodarone is reported to improve symptoms and to prevent sudden death in patients with hypertrophic cardiomyopathy (HC). Amiodarone treatment (loading dose 30 g given over 6 weeks; maintenance dose 400 mg/day) was prospectively evaluated in 50 patients with HC in whom the drug was initiated because of symptoms refractory to conventional drug therapy (calcium antagonists and beta blockers). Twenty-one (42%) patients had ventricular tachycardia (VT) during Holter monitoring. Amiodarone significantly and often markedly improved the patients' New York Heart Association functional class status (from 3.3 to 2.7 at 2 months, p less than 0.001) and treadmill exercise duration (p less than 0.001). Eight patients, however, died (7 suddenly) during a mean follow-up period of 2.2 +/- 1.8 years. Of the 7 sudden deaths, 6 occurred within 5 months of initiation of treatment. The 6-month and 1- and 2-year survival rates were 87, 85 and 80%, respectively. The survival rate of patients with VT was significantly worse than that of patients without VT (61 vs 97% at 2 years; p less than 0.01). Sudden death occurred despite abolition of VT on Holter monitoring. Amiodarone increased left ventricular peak filling rate by radionuclide angiography in 20 of 33 patients (61%) (p less than 0.01). Decrease in peak left ventricular filling rate within 10 days of amiodarone therapy (8 of 33 patients) was associated with subsequent sudden death (p less than 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal cardiac sensitivity in patients with chest pain and normal coronary arteries

The causes of chest pain in patients found to have angiographically normal coronary arteries during cardiac catheterization remain controversial. Cardiac sensitivity to catheter manipulation, pacing at various stimulus intensities and intracoronary injection of contrast medium was examined in several groups of patients who underwent cardiac catheterization. Right heart (especially right ventricular) catheter manipulation and pacing and intracoronary contrast medium provoked chest pain typical of that previously experienced in 29 (81%) of 36 patients with chest pain and angiographically normal coronary arteries and 15 (46%) of 33 symptomatic patients with hypertrophic cardiomyopathy. In contrast, only 2 (6%) of 33 symptomatic patients with coronary artery disease experienced their typical chest pain with these sensitivity tests (p less than 0.001). None of 10 patients with valvular heart disease but without a chest pain syndrome experienced any sensation with these tests. Cutaneous pain threshold testing demonstrated that patients with chest pain and normal coronary arteries had a higher pain threshold to thermal stimulation compared with patients who had coronary artery disease or hypertrophic cardiomyopathy. No relation existed between cardiac sensitivity and cutaneous sensitivity testing. Thus, patients who have chest pain despite angiographically normal coronary arteries may have abnormal cardiac sensitivity to a variety of stimuli. This increased sensitivity may be of causal importance to their chest pain syndrome or may contribute to their perception of ischemia-induced pain. The same phenomenon was also commonly seen in symptomatic patients with hypertrophic cardiomyopathy. Whether this phenomenon represents abnormal activation of pain receptors within the heart or abnormal processing of visceral afferent neural impulses in the peripheral or central nervous system is unknown.

Genetic evidence of dissociation (generational skips) of electrical from morphologic forms of hypertrophic cardiomyopathy

The diagnosis of hypertrophic cardiomyopathy (HC) is traditionally based on the demonstration by echocardiography of left ventricular hypertrophy in the absence of apparent cause. This study reports on 5 adults in 4 families who are obligate or highly probable carriers of the HC gene by virtue of their position in the pedigree, but who have normal echocardiographic findings. Four of these 5 patients had abnormal signal-averaged electrocardiograms, a finding suggesting the presence of electrical disease despite the absence of left ventricular hypertrophy. The fifth patient, an identical twin of a patient with familial HC, had neither left ventricular hypertrophy nor a myocardial electrical abnormality. These data indicate that the spectrum of HC includes patients who have a potentially arrhythmogenic left ventricular substrate but who have no evidence of left ventricular hypertrophy. Our data demonstrating generational skips also imply that some instances of HC previously judged to be sporadic may indeed by familial.

Importance of preexcited QRS morphology during induced atrial fibrillation to the diagnosis and localization of multiple accessory pathways

The present investigation evaluates the ability of several electrocardiographic (ECG) and electrophysiologic methods to identify multiple accessory pathways in 47 patients in whom the presence and sites of multiple accessory pathways were confirmed intraoperatively. To establish ECG features that suggested the presence of multiple accessory pathways in these patients, we initially studied the 12-lead ECG during maximal preexcitation in 101 patients with single accessory pathways. Distinctive 12-lead ECG patterns were noted for six defined anatomic areas around the right and left atrioventricular groove. Multiple preexcited QRS morphologies, each typical for a separate accessory pathway, and atypical preexcited QRS morphologies were recorded during atrial fibrillation in 31 of 47 (66%) patients with multiple accessory pathways. By comparison, the ECG during sinus rhythm and rapid atrial pacing identified 14 (32%) and 26 (55%) of the patients, respectively. In 12 (26%) patients in whom evidence for multiple accessory pathways was absent from endocardial mapping data, atrial fibrillation provided the diagnosis. In five (11%) patients, atrial fibrillation was the only method that demonstrated the presence of multiple accessory pathways. A combination of ECG findings during atrial fibrillation and rapid atrial pacing plus endocardial mapping data identified 43 (91%) of the patients with multiple accessory pathways. There were two unique fusion patterns on the 12-lead ECG that were characteristic of specific multiple accessory pathway combinations.(ABSTRACT TRUNCATED AT 250 WORDS)