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Biomedical subjects

B J Maron

Publications and source records attributed to B J Maron.

At least 55 records · Page 3Linked to original sources
PubMed1999

Assessment of permanent dual-chamber pacing as a treatment for drug-refractory symptomatic patients with obstructive hypertrophic cardiomyopathy. A randomized, double-blind, crossover study (M-PATHY).

BACKGROUND: Dual-chamber pacing (DDD) has been proposed as a treatment alternative to surgery for severely symptomatic patients with obstructive hypertrophic cardiomyopathy (HCM), based largely on uncontrolled studies. METHODS AND RESULTS: This prospective, multicenter trial assessed pacing in 48 symptomatic HCM patients with >/=50 mm Hg basal gradient, refractory to drug therapy. Patients were randomized to 3 months each of DDD pacing and pacing backup (AAI-30) in a double-blind, crossover study design, followed by an uncontrolled and unblinded 6-month pacing trial. With randomization, no significant differences were evident between pacing and no pacing for subjective or objective measures of symptoms or exercise capacity, including NYHA functional class, quality of life score, treadmill exercise time or peak oxygen consumption. After 6 additional months of unblinded pacing, functional class and quality of life score were improved compared with baseline (P<0.01), but peak oxygen consumption was unchanged. Outflow gradient decreased 40%, 82+/-32 mm Hg to 48+/-32 mm Hg (P<0. 001), and was reduced in 57% of patients but showed no change or an increase in 43%. At 12 months, 6 individual patients (12%) showed improved functional capacity; each was 65 to 75 years of age. Left ventricular wall thicknesses in the overall study group showed no remodeling between baseline (22+/-5 mm) and 12 months (21+/-5 mm; P=NS). CONCLUSIONS: (1) Pacing cannot be regarded as a primary treatment for obstructive HCM; (2) with randomization, perceived symptomatic improvement was most consistent with a substantial placebo effect; (3) longer, uncontrolled pacing periods were associated with some subjective benefit but unaccompanied by objective improvement in cardiovascular performance and should be interpreted cautiously; (4) modest reduction in outflow gradient was achieved in most patients; and (5) a small subset (12%) >/= 65 years of age showed a clinical response, suggesting that DDD pacing could be a therapeutic option for some elderly patients.

Adult↗
PubMed1999

Clinical course of hypertrophic cardiomyopathy in a regional United States cohort.

CONTEXT: Hypertrophic cardiomyopathy (HCM) has been regarded as a disease that causes substantial disability, with annual mortality rates of up to 6%, based largely on reports from tertiary referral centers. OBJECTIVE: To assess the clinical course of HCM in a patient cohort more closely resembling the true disease state. DESIGN: Retrospective cohort study. SETTING: A regional cohort from Minnesota and adjoining regions, free of referral center bias, studied at Minneapolis Heart Institute. PATIENTS: Two hundred seventy-seven consecutively studied HCM patients, none referred for specialized HCM care, managed clinically in a standard fashion. MAIN OUTCOME MEASURES: Mortality and clinical course of HCM. RESULTS: During a mean (SD) follow-up of 8.1 (6.6) years, 45 patients died and 29 of these deaths were directly related to HCM; however, 8 of the 29 HCM deaths were not premature (occurring >75 years of age). Annual HCM mortality rate was 1.3% (0.7% for sudden cardiac death). Patients identified in adulthood (n = 234) showed no statistically significant difference in mortality when compared with expected mortality, as calculated for the general US or Minnesota populations (P=.17). Patients identified as children (n=43) showed decreased survival compared with the general population (P<.001). At most recent clinical evaluation, 192 patients (69%) had no or mild symptoms and 69 (25%) experienced incapacitating symptoms or HCM-related death; 53 (19%) of the patients had achieved estimated life expectancy of 75 years or older. More advanced symptoms at diagnosis-occurrence of atrial fibrillation (often associated with stroke), the presence of basal outflow obstruction of at least 30 mm Hg, and marked left ventricular wall thickness of more than 25 mm-were clinically important independent predictors of HCM mortality. CONCLUSIONS: In a regionally selected patient population most closely resembling the true disease state, HCM did not significantly increase the risk of premature death or adversely affect overall life expectancy. Prevailing misconceptions of HCM as a generally unfavorable condition may largely be related to the skewed patient referral patterns characteristic of tertiary care centers. Hypertrophic cardiomyopathy is nevertheless a highly complex disease capable of serious clinical consequences and premature death in some patients.

Actuarial Analysis↗
PubMed1999

Comparison of phenotypic expression of hypertrophic cardiomyopathy in patients from the United States and Germany.

A comparison of patients with hypertrophic cardiomyopathy in the United States and Germany showed significant differences in phenotypic expression. While it is unresolved whether these observed morphologic differences were due to racial and genetic factors, or alternatively to patient selection, the awareness of such heterogeneity in the phenotypic expression of HC is relevant to interpreting clinical studies from different regions of the world.

Adult↗
PubMed1999

Physiologic left ventricular cavity dilatation in elite athletes.

BACKGROUND: Absolute left ventricular cavity dimension may be substantially increased in some highly trained athletes. This raises questions about the differential diagnosis between athlete's heart and dilated cardiomyopathy as well as possible disqualification from competitive sports. OBJECTIVE: To evaluate the morphologic characteristics and physiologic limits of left ventricular cavity enlargement associated with intensive, long-term athletic conditioning. DESIGN: Evaluation of left ventricular cavity dimension in a large sample of highly trained athletes. SETTING: Institute of Sports Science, Rome, Italy. PARTICIPANTS: 1309 elite Italian athletes (957 men and 352 women), 13 to 59 years of age (mean, 24 years), participating in 38 different sports. MEASUREMENTS: Echocardiographic assessment of left ventricular cavity dimension and multivariate statistical analysis of the determinants. RESULTS: Left ventricular end-diastolic cavity dimensions varied widely (38 to 66 mm [mean, 48 mm] in women and 43 to 70 mm [mean, 55 mm] in men) and was within generally accepted normal limits for most participants (< or = 54 mm in 725 athletes [55%]). According to an arbitrary clinical cut-point of 60 mm, the left ventricular cavity was substantially enlarged in 185 participants (14%). These athletes had global left ventricular systolic function within normal limits and no regional wall-motion abnormalities; participants remained free of cardiac symptoms and impaired performance over 1 to 12 years (mean, 4.7 years). The major determinants of cavity dimension were greater body surface area and participation in certain endurance sports (cycling, cross-country skiing, and canoeing). CONCLUSIONS: In a sample of highly trained athletes, left ventricular cavity dimension varied widely but was strikingly increased to a degree compatible with primary dilated cardiomyopathy in almost 15% of participants. In the absence of systolic dysfunction, this cavity dilatation is most likely an extreme physiologic adaptation to intensive athletic conditioning. The long-term consequences and significance of this marked left ventricular remodeling of the athlete's heart is not known.

Adolescent↗
PubMed1999

Clinical profile of hypertrophic cardiomyopathy identified de novo in rural communities.

OBJECTIVES: The purpose of this study was to assess the extent to which hypertrophic cardiomyopathy (HCM) exists unsuspected and undetected in the general population. BACKGROUND: Hypertrophic cardiomyopathy is a disease with diverse natural history for which the potential to produce adverse consequences has been emphasized. However, the possibility of this disease remaining clinically dormant for many years has not been as widely appreciated. Certainly, the clinical recognition of previously undiagnosed patients with HCM may be advantageous by permitting risk stratification for sudden cardiac death or for timely pharmacologic therapy when symptoms intervene. METHODS: We prospectively conducted an echocardiographic survey in 64 primarily rural communities within Minnesota (populations < 10,000) over a 33-month period. RESULTS: A total of 15,137 echocardiograms were performed at the request of primary care physicians for the purpose of excluding cardiovascular abnormalities. Hypertrophic cardiomyopathy was identified in 44 patients during the survey (0.29%), and 29 of these patients (0.19% of the 15,137 echocardiograms) had not been previously identified as having cardiac disease or HCM. At diagnosis, ages were 16 to 87 years (mean 57); 14 patients were > or = 60 years of age, and only two were < 30 years. Twenty-four patients (83%) had either no or only mild or transient symptoms; 5 (17%) evidenced severe functional limitation; in eight patients the onset of symptoms had been deferred until > or = 70 years of age. Basal left ventricular outflow obstruction (gradients 20 to 82 mm Hg) was evident in 11 patients (38%). Relatively mild phenotypic expression of the disease was substantiated by localized patterns of left ventricular wall thickening occurring more commonly than diffusely distributed hypertrophy (48% vs. 7%, respectively), and electrocardiograms that were frequently normal (about 25%) and rarely showed evidence of left ventricular hypertrophy (10%). CONCLUSIONS: These prospectively assembled data show that HCM may remain clinically dormant and undetected within community-based rural populations for many years (often to advanced ages) with a not inconsequential prevalence similar to that of HCM in the general population.

Adolescent↗
PubMed1999

Prognostic value of systemic blood pressure response during exercise in a community-based patient population with hypertrophic cardiomyopathy.

OBJECTIVES: The present study was designed to prospectively evaluate the prognostic relevance of abnormal blood pressure response to exercise (ABPR), defined as hypotension or failed blood pressure increase (<20 mm Hg) with exercise, in a community-based hypertrophic cardiomyopathy (HCM) population representative of the overall disease spectrum. BACKGROUND: Abnormal blood pressure response to exercise has been proposed as a marker for hemodynamic instability and increased risk for disease-related mortality in highly selected patient populations with HCM. METHODS: The study population comprised 126 patients (aged 42+/-14 years) who underwent maximal symptom-limited cycloergometer exercise testing as part of the standard evaluation at our institution, and who were followed systematically for 4.7+/-3.7 years after testing. RESULTS: Of the 126 study patients, 98 (78%) had a normal blood pressure response during exercise, whereas the other 28 (22%) had ABPR, including nine with hypotension and 19 with failed blood pressure rise. During the follow-up period, nine patients (7%) died of HCM-related causes (three suddenly and six heart failure-related), of whom four had ABPR. In those patients aged < or =50 years, survival analysis after exercise testing showed a significantly increased risk for cardiovascular mortality associated with ABPR compared with a normal exercise response (p = 0.04), with an odds ratio of 4.5 (95% confidence interval: 1.1, 20.1). However, ABPR showed low positive predictive accuracy for cardiovascular mortality (i.e., 14%), whereas negative predictive accuracy was high (i.e., 95%). CONCLUSIONS: A hypotensive blood pressure response during exercise occurred in over 20% of a community-based patient cohort with HCM, and was associated with adverse long-term prognosis in patients <50 years old. However, the positive predictive accuracy of this blood pressure response is too low to justify modifications of clinical management or to allow identification of the high-risk patient based solely on an abnormal test result. By virtue of its high negative predictive accuracy for HCM-related mortality, the blood pressure response to exercise appears to be most valuable (in conjunction with the absence of other well recognized risk factors) as a screening test for the identification of low-risk subsets of patients.

Adult↗
PubMed1999

Clinical profile of commotio cordis: an under appreciated cause of sudden death in the young during sports and other activities.

Not particularly well recognized are athletic field catastrophes in which virtually instantaneous cardiac arrest is produced by nonpenetrating chest blows in the absence of heart disease or identifiable morphologic injury to the chest wall or heart (commotio cordis). To better characterize the clinical profile of this syndrome, we have assembled 70 cases, including 34 occurring during organized competitive athletics and 36 others that occurred during informal recreational sports at home, school or the playground, or during nonsporting activities. Ages were 2 to 38 (mean age: 12) with 70% < 16 years old. Most common sports involved were youth baseball (n = 40), softball (n = 7), and ice hockey (n = 7). Seven (10%) of the 70 commotio cordis victims, including six with documented ventricular fibrillation, have survived the consequences of their chest blow. Eleven of the events (16%) occurred despite the presence of chest padding believed to be potentially protective. Four victims experienced modest chest blows while in circumstances completely unrelated to sports activities; three of the four individuals who delivered these blows were ultimately convicted of criminal acts within the justice system. An experimental model of low-energy chest wall impact demonstrates that commotio cordis events are due largely to the exquisite timing of blows during a narrow window within the repolarization phase of the cardiac cycle, 15 to 30 msec prior to the peak of the T wave.

Adolescent↗
PubMed1998

Pitfalls in clinical recognition and a novel operative approach for hypertrophic cardiomyopathy with severe outflow obstruction due to anomalous papillary muscle.

BACKGROUND: Ventricular septal myotomy/myectomy (Morrow procedure) is the standard surgical option for severely symptomatic patients with hypertrophic cardiomyopathy (HCM) and marked basal obstruction to left ventricular outflow due to mitral valve systolic anterior motion. In some patients, however, congenital malformations of the mitral apparatus may be responsible for outflow obstruction; the failure to recognize this morphology before operation could have adverse consequences. METHODS AND RESULTS: We recently evaluated 2 patients with obstructive HCM operated on at Mayo Medical Center in 1997 who demonstrated direct anomalous papillary muscle insertion into the anterior mitral leaflet, producing muscular midcavity obstruction. This anomaly is potentially identifiable with echocardiography by exaggerated anterior displacement of hypertrophied papillary muscles within the left ventricular cavity and the direct continuity between papillary muscle and anterior leaflet associated with a rigid motion pattern of the mitral apparatus. Echocardiographic diagnosis, however, was confused in both patients by the association of systolic anterior motion of the mitral valve, probably produced by freely mobile margins of the mitral leaflet unencumbered by papillary muscle insertion, and in 1 patient probably representing a second and more basal level of obstruction. Because outflow tract morphology was judged unsuitable for conventional myotomy/myectomy, a novel surgical strategy was designed to remove the outflow gradient in which an extensive myectomy trough (wider at its apical than basal extent) was created within the ventricular septum to papillary muscle level; also, in 1 patient, attachment of anterolateral papillary muscle with the lateral free wall was partially severed to increase mobility of the mitral apparatus. After surgery, both patients reported substantial relief of symptoms and improved exercise tolerance and also showed reduced or abolished basal outflow obstruction. CONCLUSIONS: In HCM, outflow obstruction due to anomalous papillary muscle insertion directly into anterior mitral leaflet is challenging to identify but should always be contemplated before operative intervention. This important (but often unsuspected) congenital malformation may require alternative surgical strategies to standard myotomy/myectomy, similar to those described here.

Adolescent↗
PubMed1998

Cardiovascular risks to young persons on the athletic field.

Sudden cardiac deaths of young athletes, which are usually associated with physical exertion, continue to achieve high public visibility and generate considerable concern. Despite broad community participation in sports, such catastrophes are uncommon, occurring in about 1/200000 high school athletes per academic year. Various unsuspected congenital cardiovascular diseases are usually responsible; the most common lesions are hypertrophic cardiomyopathy and several congenital coronary artery anomalies. Selected reports suggest that arrhythmogenic right ventricular dysplasia may be a more common cause of these deaths than previously suspected. In some trained athletes with borderline increases in thickness of the left ventricular wall, mild morphologic expression of hypertrophic cardiomyopathy can often be distinguished from the physiologic consequences of athlete's heart by noninvasive clinical assessment and testing. In addition, the recognized cardiovascular risks of the athletic field are now extended to include cardiac arrest resulting from relatively modest, nonpenetrating chest blows produced by projectiles (such as baseballs) or bodily contact in the absence of underlying cardiac disease and without structural injury to the chest wall or heart. These uncommon but usually fatal events seem to result when chest impact occurs precisely during the vulnerable phase of repolarization, and they may be reduced by use of softer baseballs. Preparticipation screening for cardiovascular disease, consisting of standard history and physical examination, is customary practice for most high school and college athletes in the United States. Evidence suggests, however, that the present screening process for cardiovascular disease in high school athletes may be largely inadequate, given the content of the approved screening questionnaires (which serve as guidelines for the process) and the use of examiners with little cardiovascular training. This emphasizes the need for national standardization of preparticipation screening. The recommendations of the 26th Bethesda Conference for disqualification from competitive athletics are now a standard for management decisions when cardiovascular abnormalities are identified in trained athletes.

Cardiovascular Diseases↗
PubMed1998

Congenital heart disease caused by mutations in the transcription factor NKX2-5.

Mutations in the gene encoding the homeobox transcription factor NKX2-5 were found to cause nonsyndromic, human congenital heart disease. A dominant disease locus associated with cardiac malformations and atrioventricular conduction abnormalities was mapped to chromosome 5q35, where NKX2-5, a Drosophila tinman homolog, is located. Three different NKX2-5 mutations were identified. Two are predicted to impair binding of NKX2-5 to target DNA, resulting in haploinsufficiency, and a third potentially augments target-DNA binding. These data indicate that NKX2-5 is important for regulation of septation during cardiac morphogenesis and for maturation and maintenance of atrioventricular node function throughout life.

Amino Acid Sequence↗
PubMed1998

An experimental model of sudden death due to low-energy chest-wall impact (commotio cordis)

BACKGROUND: The syndrome of sudden death due to low-energy trauma to the chest wall (commotio cordis) has been described in young sports participants, but the mechanism is unknown. METHODS: We developed a swine model of commotio cordis in which a low-energy impact to the chest wall was produced by a wooden object the size and weight of a regulation baseball. This projectile was thrust at a velocity of 30 miles per hour and was timed to the cardiac cycle. RESULTS: We first studied 18 young pigs, 6 subjected to multiple chest impacts and 12 to single impacts. Of the 10 impacts occurring within the window from 30 to 15 msec before the peak of the T wave on the electrocardiogram, 9 produced ventricular fibrillation. Ventricular fibrillation was not produced by impacts at any other time during the cardiac cycle. Of the 10 impacts sustained during the QRS complex, 4 resulted in transient complete heart block. We also studied whether the use of safety baseballs, which are softer than standard ones, would reduce the risk of arrhythmia. A total of 48 additional animals sustained up to three impacts during the T-wave window of vulnerability to ventricular fibrillation with a regulation baseball and safety baseballs of three degrees of hardness. We found that the likelihood of ventricular fibrillation was proportional to the hardness of the ball, with the softest balls associated with the lowest risk (two instances of ventricular fibrillation after 26 impacts, as compared with eight instances after 23 impacts with regulation baseballs). CONCLUSIONS: This experimental model of commotio cordis closely resembles the clinical profile of this catastrophic event. Whether ventricular fibrillation occurred depended on the precise timing of the impact. Safety baseballs, as compared with regulation balls, may reduce the risk of commotio cordis.

Animals↗
PubMed1998

Profile of preparticipation cardiovascular screening for high school athletes.

CONTEXT: Sudden death in young competitive athletes due to unsuspected cardiovascular disease has heightened concern and interest in the preparticipation screening available to high school athletes in the United States. OBJECTIVE: To assess the potential adequacy of the preparticipation screening process for detecting or increasing the suspicion of cardiovascular abnormalities. DESIGN: Current guidelines and requirements for implementation of preparticipation screening from each of the high school jurisdictions in the 50 states and the District of Columbia were analyzed and compared with the 1996 American Heart Association (AHA) consensus panel guidelines on screening. OUTCOME MEASURES: Items contained on preparticipation screening questionnaires; the examiners designated to perform screening. RESULTS: Eight states (16%) have no approved history and physical examination questionnaires to guide examiners, including 1 state without a formal screening requirement. Of the remaining 43 states, several items relevant to cardiac-related problems were frequently omitted from the questionnaires. Exertional dyspnea or chest pain, prior limitation from sports, family history of heart disease, or Marfan syndrome were included in 0% to 56% of the state forms. Specific cardiovascular items on physical examination were included in forms from only 5% to 37% of states, including documentation of a heart murmur, irregular heart rhythm, peripheral pulses, or stigmata of Marfan syndrome. Seventeen (40%) of 43 states had history and physical questionnaires judged to be most adequate with at least 9 of the 13 AHA recommendations, whereas 12 states (28%) were least adequate with 4 or less of these recommended items. Therefore, a total of 20 (40%) of the 51 states have no approved history and physical examination questionnaires, or formal screening requirement, or forms that were judged to be inadequate. In addition to physicians, 21 states also permit nurses or physician assistants to administer examinations, and 11 states specifically provide for practitioners with limited cardiovascular training (such as chiropractors). CONCLUSIONS: Preparticipation athletic screening for cardiovascular disease with standard history and physical examination, as presently employed in US high schools, is highly dependent on the state-approved questionnaires, which frequently are abbreviated and may be inadequate; is implemented by a variety of health care workers with varying levels of expertise; and may be severely limited in its power to detect potentially lethal cardiovascular abnormalities. These observations should represent an impetus for change and improvement in the preparticipation cardiovascular screening process for high school athletes.

Adolescent↗