Reversal of acute pulmonary oedema with beta-blockers in hypertrophic cardiomyopathy.
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Adrenergic beta-Antagonists↗
Biomedical subjects
M S Hamid
Publications and source records attributed to M S Hamid.
Pregnancy related complications in women with hypertrophic cardiomyopathy.
OBJECTIVES: To determine whether pregnancy is well tolerated in hypertrophic cardiomyopathy. SETTING: Referral clinic. DESIGN: The study cohort comprised 127 consecutively referred women with hypertrophic cardiomyopathy. Forty (31.5%) underwent clinical evaluation before pregnancy. The remaining 87 (68.5%) were referred after their first pregnancy. All underwent history, examination, electrocardiography, and echocardiography. Pregnancy related symptoms and complications were determined by questionnaire and review of medical and obstetric records where available. RESULTS: There were 271 pregnancies in total. Thirty six (28.3%) women reported cardiac symptoms in pregnancy. Over 90% of these women had been symptomatic before pregnancy. Symptoms deteriorated during pregnancy in fewer than 10%. Of the 36 women with symptoms during pregnancy, 30 had further pregnancies. Symptoms reoccurred in 18 (60%); symptomatic deterioration was not reported. Heart failure occurred postnatally in two women (1.6%). No complications were reported in 19 (15%) women who underwent general anaesthesia and in 22 (17.4%) women who received epidural anaesthesia, three of whom had a significant left ventricular outflow tract gradient at diagnosis after pregnancy. Three unexplained intrauterine deaths occurred in women taking cardiac medication throughout pregnancy. No echocardiographic or clinical feature was a useful indicator of pregnancy related complications. CONCLUSIONS: Most women with hypertrophic cardiomyopathy tolerate pregnancy well. However, rare complications can occur and therefore planned delivery and fetal monitoring are still required for some patients.
Adult↗
Hypertrophic cardiomyopathy: management issues in the new millennium.
Hypertrophic cardiomyopathy is an inherited cardiac disorder. Sudden cardiac death frequently occurs in otherwise healthy individuals, and accounts for nearly 35% of all sudden deaths within this age group. Although symptoms occur commonly, they often go unreported. Despite this, a degree of functional limitation is often seen on objective assessment. Management of hypertrophic cardiomyopathy is aimed at relieving symptoms, identifying and treating those individuals at increased risk of sudden death, and screening family members.
Age of Onset↗
Septal myotomy-myectomy and transcoronary septal alcohol ablation in hypertrophic obstructive cardiomyopathy. A comparison of clinical, haemodynamic and exercise outcomes.
AIMS: Surgical myectomy has been successfully used to treat patients with symptomatic obstructive hypertrophic cardiomyopathy (HCM). More recently, alcohol septal ablation has been advocated as a less invasive, but equally effective alternative therapy. The aim of this non-randomized cohort study was to compare subjective and objective outcomes in patients undergoing these therapies. METHODS: Forty-four patients (25 male; age 41+/-15 years) with symptomatic drug-refractory obstructive HCM were studied. Twenty-four patients underwent surgical myectomy and 20 alcohol septal ablation. All patients underwent clinical evaluation, echocardiography and upright maximal cardiopulmonary exercise testing using a cycle ergometer before and following their intervention. RESULTS: Peak gradient was reduced to a similar extent by both modalities (myectomy: 83+/-23 to 15+/-10 mmHg (P<0.000001); ablation: 91+/-18 to 22+/-14 mmHg (P<0.000002);P =0.48 for myectomy vs ablation) and led to similar improvements in NYHA class (myectomy: 2.4+/-0.6 to 1.5+/-0.7 (P<0.00001); ablation: 2.3+/-0.5 to 1.7+/-0.8 (P<0.0001);P=0.3 for myectomy vs ablation). Myectomy resulted in a greater improvement in peak oxygen consumption (myectomy: 16.4+/-5.8 to 23.1+/-7.1 ml.kg(-1) min(-1) (P<0.00002); ablation: 16.2+/-5.2 to 19.3+/-6.1 ml.kg(-1) min(-1) (P<0.05);P <0.05 for myectomy vs ablation) and work rate achieved (myectomy: 130+/-57 to 161+/-60 watts (P<0.04); ablation: 121+/-53 to 137+/-51 watts (P=0.11);P <0.05 for myectomy vs ablation). CONCLUSION: Surgical myectomy and alcohol septal ablation are equally effective at reducing obstruction and subjective exercise limitation in appropriately selected patients. However, the superior effect of surgical myectomy on exercise test parameters suggests that surgery remains the gold standard against which new treatment modalities should be compared.
Adult↗
Shear stress distribution in the trabeculae of human vertebral bone.
The statistical distribution of von Mises stress in the trabeculae of human vertebral cancellous bone was estimated using large-scale finite element models. The goal was to test the hypothesis that average trabecular von Mises stress is correlated to the maximum trabecular level von Mises stress. The hypothesis was proposed to explain the close experimental correlation between apparent strength and stiffness of human cancellous bone tissue. A three-parameter Weibull function described the probability distribution of the estimated von Mises stress (r2>0.99 for each of 23 cases). The mean von Mises stress was linearly related to the standard deviation (r2=0.63) supporting the hypothesis that average and maximum magnitude stress would be correlated. The coefficient of variation (COV) of the von Mises stress was nonlinearly related to apparent compressive strength, apparent stiffness, and bone volume fraction (adjusted r2=0.66, 0.56, 0.54, respectively) by a saturating exponential function [COV = A + B exp(-x/C)]. The COV of the stress was higher for low volume fraction tissue (<0.12) consistent with the weakness of low volume fraction tissue and suggesting that stress variation is better controlled in higher volume fraction tissue. We propose that the average stress and standard deviation of the stress are both controlled by bone remodeling in response to applied loading.
Adult↗
Severe urological complication of leech bite in the tropics.
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Agricultural Workers' Diseases↗
Effects of cyclic flexion of coronary arteries on progression of atherosclerosis.
The purpose of this investigation was to test the hypothesis that cyclic flexion of the coronary arteries contributes to the progression of atherosclerotic plaques. Coronary arteriograms were evaluated in 33 unselected patients who underwent 2 studies over a period of 25 +/- 16 months (mean +/- SD). Among the 33 patients, 103 plaques were identified. Plaques that showed progression were compared with plaques that showed no progression. The angle of flexion that occurred during systole at the site of the plaque was measured on the first arteriogram. In comparing progression versus no progression, the interval between arteriograms was 29 +/- 18 versus 23 +/- 14 months (p = NS) and percent stenosis at the first arteriogram was 42 +/- 28 versus 45 +/- 19% (p = NS). Percent stenosis at the time of the second arteriogram among plaques that progressed was 78 +/- 21%, and by definition, it remained 45 +/- 19% among those that did not progress. Among arteries with plaques that showed a progression of stenosis, the angle of flexion during systole was 19 +/- 13 degrees versus 9 +/- 15 degrees among arteries with plaques that did not progress (p < 0.01). Linear regression showed that the correlation of the angle of flexion with percent change of stenosis was relatively low (r = 0.32) but statistically significant (p < 0.005). Mathematic modeling of flexible and stiff plaques showed stresses approximately 1.5 to 1.9 times greater with 20 degrees than with 10 degrees flexion. Stresses due to flexion were usually greatest proximal and distal to the plaque along the subendothelial layer of the inner wall of the curved vessel. Data show that the angle of cyclic flexion, and consequently the stresses due to cyclic flexion of the artery were greatest in the region of plaques that progressed over the period of observation. Such stresses may have contributed to tissue damage of fatigue resulting in a more rapid progression of the atheromatous plaques.
Aged↗
Acute glomerulonephritis in Kelantan--a prospective study.
A prospective study of acute nephritis in children was conducted at the Universiti Sains Malaysia Hospital, Kubang Kerian between July 1987 and June 1988. One hundred and twenty four children were admitted with acute glomerulonephritis. The aim of the study was to determine the clinical pattern of the nephritis as well as its aetiology. The majority of our patients came from the lower socio-economic group and 54% of the families had incomes below the poverty line. Preceding skin infection was much more common than throat infection. The children showed a high incidence of complications: severe hypertension (43.6%), hypertensive encephalopathy (11.3%), clinical pulmonary oedema (36.3%), severe azotaemia (10.5%), and prolonged gross haematuria (13.7%). By using immunologic indices such as ASOT, anti-DNase B and complement 3, it was concluded that 121 of the 124 patients had post-streptococcal nephritis.
Acute Disease↗
Mechanical factors in the degeneration of porcine bioprosthetic valves: an overview.
Predilection of certain sites of the porcine bioprosthetic valve (PBV) leaflets to calcification and tissue disruption has provoked suggestions that design factors and mechanical stresses may be major reasons leading to degeneration. In recent years, computer based numerical models of PBVs have shown a close association between sites of leaflet calcification and disruption and sites of leaflet stress concentration. These numerical models have also provided a means through which methodical design optimization can be carried out. Increasing stent flexibility, for instance, was shown to lead to an overall reduction of mechanical stresses on the PBV leaflets. Reducing the stent height, on the other hand, was accompanied by an undesirable increase of overall leaflet stresses. Despite encouraging work in this field, more research is needed to further elucidate means by which the structural integrity of bioprosthetic valves can be preserved through a minimization of the adverse effects of mechanical stresses.
Animals↗
Effect of alcohol upon arrhythmias following nonpenetrating cardiac impact.
The purpose of this study was to determine if alcohol worsens arrhythmias produced by nonpenetrating cardiac impact. Twenty-three dogs were studied. Twelve underwent nonpenetrating cardiac impact alone at 12 m/sec with a contact compression of 2 cm. Eleven underwent cardiac impact after having received intravenous alcohol (blood level of 197 +/- 37 mg/100 ml) (mean +/- SD). Three dogs experienced ventricular fibrillation immediately after impact and died: of these, two underwent impact alone and one underwent impact following ethanol. These three dogs were eliminated from the study. All of the dogs had some form of complex arrhythmia during the first 10 minutes of observation, the average cumulative duration of which during the first 10 minutes following trauma was greater among dogs that received ethanol. No complex arrhythmias other than ventricular premature contractions or ventricular tachycardia were observed after the first 10 minutes following impact. During the first 2 hours of observation following cardiac impact, dogs that received alcohol before trauma showed more single premature ventricular contractions (p less than 0.03), couplets (p less than 0.01), triplets (p less than 0.02), runs of 4-20 beats (p less than 0.05), and total number of premature ventricular contractions (p less than 0.05) than dogs that underwent trauma alone. Following the first 10 minutes, ventricular irritability increased with time until approximately 1 hour, and then there was a gradual reduction of the frequency of arrhythmias in both dogs that received alcohol and those that did not. In conclusion, nonpenetrating cardiac impact in dogs that previously received ethanol was associated with greater ventricular irritability than in dogs that underwent impact alone.
Animals↗
Vibrational analysis of bioprosthetic heart valve leaflets using numerical models: effects of leaflet stiffening, calcification, and perforation.
The fundamental natural frequency of the closed cusps of porcine bioprosthetic valves, fabricated from the normal leaflets of pig aortic valves, was estimated using a finite element model. Both normal and stiffened leaflets were considered in the vibrational analysis. The effects of conditions that simulated degeneration, such as stiffening, central perforation, a tear, calcium deposits in the commissural attachments, and combinations of these were determined. The primary frequency of vibration of the normal leaflets was within the range of the dominant frequency of the heart sounds determined clinically by spectral analysis of the recorded phonocardiogram. If only one leaflet was stiffened or calcified, there was only a marginal change of frequency. With stiffening and calcification of the commissures of all 3 leaflets, the frequency of vibration increased. Introduction of a tear in a single leaflet of a stiffened and calcified valve markedly reduced the fundamental frequency. In view of the relation between the frequency content of heart sounds and the frequency of valve vibration, this mathematical simulation establishes a possible basis for the observation of a varying dominant frequency of heart sounds in patients with bioprosthetic valves that are in the process of degenerating.
Biomechanical Phenomena↗
Influence of stent height upon stresses on the cusps of closed bioprosthetic valves.
A finite element model of a bioprosthetic heart valve was developed to determine the influence of the stent height on leaflet stresses under various pressure loading conditions after valve closure. A nonlinear solution was used to obtain the stresses in the leaflets for stent heights of 14.6 mm, 19.0 mm and 22.0 mm respectively. The basic assumptions included an elliptic-paraboloid for a relaxed leaflet shape, a rigid stent, isotropic leaflet material property with a Poisson's ratio of 0.45, a uniform leaflet thickness and a stress dependent Young's modulus. The model predicted an increase of stresses on the closed leaflets as the stent height was reduced. This observation appears to mitigate, to some extent, the hemodynamic benefits thought to accompany the reduction of stent height of bioprosthetic valves.
Bioprosthesis↗
Mechanical stresses on closed cusps of porcine bioprosthetic valves: correlation with sites of calcification.
The purpose of this study was to (1) evaluate the magnitude and distribution of mechanical stresses on closed leaflets of porcine bioprosthetic valves (PBVs) by using a nonlinear, finite-element model, and (2) determine if a relationship exists between the magnitude of stresses at various sites on the leaflet and the incidence of calcification at those sites. Mechanical stresses were found to be highest near the commissures and lowest at the base of the leaflet. At a pressure of 100 mm Hg applied to the closed valve, the maximal principal normal stress was 160 kPa near the commissures, 140 kPa in the body of the leaflet, 70 kPa at the free margin, and 60 kPa near the base. Similarly, the maximal shear stress, at an applied pressure of 100 mm Hg, was 80 kPa near the commissures, 70 kPa in the body of the leaflet, 50 kPa at the free margin, and 40 kPa near the base. This distribution of mechanical stresses on the PBV leaflet coincided with the incidence of calcification of the various regions of the leaflet. Calcification was found most frequently near the commissures, less frequently in the body of the leaflet and free margin, and least frequently at the base. These observations suggest a possible causative relation between the magnitude of mechanical stresses and the site of calcification of PBV leaflets.
Bioprosthesis↗
Estimation of mechanical stresses on closed cusps of porcine bioprosthetic valves: effects of stiffening, focal calcium and focal thinning.
The magnitude and distribution of mechanical stresses acting on the closed cusps of porcine bioprosthetic valves (PBVs) were estimated using a finite element model. The effects of leaflet stiffening, focal calcium and focal thinning on leaflet stresses were determined. In a normal closed PBV leaflet, stresses increased as pressure was increased. At a pressure of 80 mm Hg, the maximal normal principal stresses were 11 g/mm2 near the center of the leaflet and increased to 19 g/mm2 at a pressure of 160 mm Hg. These observations suggest that the closed valve in the mitral position would experience higher mechanical stresses than the closed valve in the aortic position. Tissue stiffening increased stresses throughout the leaflet and introduced a site of stress concentration near the center of the leaflet. At a pressure of 80 mm Hg, the maximal principal normal stress increased 55% when the leaflet was stiff in comparison to the normal leaflet. Focal calcium and focal thinning caused marked gradients of stress between the sites of calcium or thinning and the immediate surrounding tissue. The magnitude of these stress gradients increased with increasing pressure. These sites of mechanical stress concentration or stress gradients appear to be compatible with sites of leaflet calcification or disruption. Such stresses may contribute to spontaneous degeneration of PBVs.
Aortic Valve↗
Computer-assisted methods for design optimization of cardiac bioprosthetic valves.
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Bioprosthesis↗
Finite element stress analysis of the human left ventricle whose irregular shape is developed from single plane cineangiocardiogram.
The three-dimensional left ventricular chamber geometrical model is developed from single plane cineangiocardiogram. This left ventricular model is loaded by an internal pressure monitored by cardiac catheterization. The resulting stresses in the left ventricular model chamber's wall are determined by computerized finite element procedure. For the discretization of this left ventricular model structure, a 20-node, isoparametric finite element is employed. The analysis and formulation of the computerised procedure is presented in the paper, along with the detailed algorithms and computer programs. The procedure is applied to determine the stresses in a left ventricle at an instant, during systole. Next, a portion (represented by a finite element) of this left ventricular chamber is simulated as being infarcted by making its active-state modulus value equal to its passive-state value; the neighbouring elements are shown to relieve the "infarcted" element of stress by themselves taking on more stress.
Angiocardiography↗