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Biomedical subjects

D R Redwood

Publications and source records attributed to D R Redwood.

At least 37 records · Page 2Linked to original sources
PubMed1976

Relation between echocardiographically determined left atrial size and atrial fibrillation.

In an attempt to define quantitatively the relation between left atrial size and atrial fibrillation, echocardiography was used to study 85 patients with isolated mitral valve disease, 50 patients with isolated aortic valve disease, and 130 patients with asymmetric septal hypertrophy. In all three groups of patients, atrial fibrillation was rare when left atrial dimension was below 44 mm (3 of 117 or 3%) but common when this dimension exceeded 40 mm (80 of 148 or 54%). In addition, when left atrial dimension exceeds 45 mm, cardioversion, while initially successful, is unlikely to produce sinus rhythm that can be maintained at least six months. These data suggest that left atrial size is an important factor in the development of atrial fibrillation and in determining the long term result of cardioversion. The pathophysiologic mechansim most consistent with this is that a chronic hemodynamic burden initially produces left atrial enlargement which in turn predisposes to atrial fibrillation. Only prospective studies will determine definitively whether these observations will be useful in decisions concerning prophylactic anticoagulation and elective cardioversion.

Adolescent↗
PubMed1976

Tunnel subaortic stenosis: left ventricular outflow tract obstruction produced by fibromuscular tubular narrowing.

The clinical and morphologic features of tunnel subaortic stenosis, an unusual form of obstruction to left ventricular outflow, are described in 11 patients. Although patients with tunnel subaortic stenosis demonstrate a variety of cardiovascular malformations, the most characteristic anatomic feature is fibromuscular tubular narrowing of the outflow tract that remains relatively unchanged during the cardiac cycle. The aortic anulus was abnormally small in six of the 11 patients, including one who also had a hypoplastic ascending aorta. Evidence of a small mitral orifice was present in two patients, and two other patients had asymmetric septal hypertrophy. Although operation was successful in significantly reducing the outflow gradient in two of the seven operated patients, all seven patients had gradients of 50 mm Hg or more at the most recent postoperative evaluation. Three patients (two with previous operation) died suddenly; each of these patients had mild or no symptoms. Because of the apparent ineffectiveness of current operative methods in patients with tunnel subaortic stenosis, it is important to differentiate this condition from obstructions to left ventricular outflow.

Adolescent↗
PubMed1976

Protection of ischemic myocardium by nitroglycerin: experimental and clinical results.

Nitroglycerin (NTG) traditionally has bben avoided in the treatment of pain caused by acute myocardial infarction because of the belief that NTG-induced decrease in arterial pressure and concomitant reflex increase in heart rate might extend the ischemic process. However, recent experimental and clinical investigations cast doubt on this concept. For example, when the left anterior descending coronary artery is acutely occluded in normal dogs or in dogs when chronic coronary occlusions and extensive collaterals, NTG reduces ST-segment evevation (and presumably myocardial ischemia). This salutary effect occurs despite lowering of systemic arterial pressure, as long as excessive reflex tachycardia does not result; the magnitude of ischemia reduction is potentiated when methoxamine or phenylephrine are administered simultaneously to abolish the NTG -induced hypotension and reflex tachycardia. NTG and methoxamine treatment also results in 1) reduction of infarct size as (as assessed by gross morphologic examinations and myocardial CPK levels) in dogs subjected to 5 hours of coronary occlusion, and 2) increase in ventricular fibrillation (VF) threshold and reduction of the incidence of spontaneously occurring VF in dogs with acute coronary occlusion. Finally, the effectiveness of NTG during acute myocardial iinfarction (AMI) in man has been studied. Multiple precordial electrodes were used to measure changes in the degree of ST-segment elevation; these changes were used as an index of alterations in myocardial ischemic injury. Patients with normal pulmonary capillary wedge pressures ( less than 15 mm Hg) did not benefit consistently from NTG alone; however, when phenylephrine was administered with NTG (to abolish NTG-induced arterial pressure reduction and reflex increase in heart rate), ST-segment elevation diminished consistently. In patients with elevated wedge pressures ( greater than 15 mm Hg), NTG alone consistently reduced ischemia; addition of phenylephrine often partially reversed this benefit. Thus, administration of NTG, alone or with phenylephrine, appears to reduce myocardial ischemic injury during AMI in man; however, the response to phenylephrine depends upon the presence or absence of LV failure prior to treatment. These experimental and clinical results suggest this form of therapy may be use in reducing infarct size in man, although additional studies are necessary to determine the functional significance of these acute electrophysiologic alterations.

Animals↗
PubMed1975

Reduction in myocardial ischemia with nitroglycerin or nitroglycerin plus phenylephrine administered during acute myocardial infarction.

Nitroglycerin reduces ischemic injury during acute myocardial infarction (AMI) in dogs--an effect that is potentiated when drug-induced hypotension and tachycardia are prevented with phenylephrine. To determine the effectiveness of nitroglycerin, alone or with phenylephrine, during AMI in man, 12 patients (five or whom had left heart failure) were evaluated by summing ST-segment abnormalities (sigmaST) from 35 precordial electrodes. The seven patients without heart failure did not benefit consistently from nitroglycerin alone; however, addition of phenylephrine to abolish nitroglycerin-induced arterial pressure reduction uniformly diminished sigmaST (4.9 to 3.2 mv; P less than 0.05). In patients with heart failure, nitroglycerin alone consistently reduced ischemia (5.8 to 4.4 mv, P less than 0.05); addition of phenylephrine often partially reversed this effect. Thus, administration of nitroglycerin, alone or with phenylephrine, can reduce myocardial ischemic injury during AMI in man; however, the response to phenylephrine depends on the presence or absence of left ventricular failure before treatment.

Acute Disease↗
PubMed1975

Limitations of the electrocardiographic response to exercise in predicting coronary-artery disease.

The electrocardiographic response to exercise was compared with the results of coronary angiography in 89 patients with Type II hyperlipoproteinemia who had previous myocardial infarction or typical angina or both (43 patients)(Group A), "atypical angina" (16 patients)(Group B)or positive electrocardiographic response to exercise without other evidence of cardiac disease (30 patients)(Group C). Thirty-nine of 43 in Group A had greater than or equal to 50 per cent stenosis, and 26 (67%) of these 39 had negative exercise tests. In Group B, five of the 16 had greater than or equal to 50% stenosis, and three had positive exercise tests (one patient had a false-positive test). In Group C, eleven of 30(37%) had greater than or equal to 50% stenosis; however, nine (30%) had minor stenosis (less than or equal to 50%), and 10(33%) normal coronary arteries. The diagnostic usefulness of exercise electrocardiography is limited. False-negative responses are frequent in patients with clinically suspected coronary disease, and false-positive responses frequent in asymptomatic patients.

Adult↗
PubMed1975

Measurement of ejection fraction in man by videodensitometry.

This report describes a new method based on roentgen videodensitometry for the measurement of left ventricular ejection fraction in man. The net forward ejection fraction (NFEF) is calculated directly from the formula NFEF=1-exp(-.693/N), where N is the number of cardiac cycles necessary for half of the injected contrast material to be washed out of the left ventricle. The derivation of this formula is presented, and the technique is validated by comparison with washout curves from a Lucite model of the heart and with simultaneous angiographically determined left ventricular ejection fractions in man. The videodensitometry technique offers the following advantages over the conventional volume technique: (1) only a small amount of contrast material is required; (2) ectopic beats are uncommon during the washout phase when measurements are made; (3) the ejection fraction measured is an average of several cardiac cycles; and (4) dependence upon operator interpretation is minimized. Furthermore, given adequate mixing within the chamber, NFEF should be independent of ventricular geometry. Thus, NFEF of the unusually shaped left ventricle can be readily determined.

Absorptiometry, Photon↗
PubMed1975

Saphenous vein bypass grafts: Long-term patency and effect on the native coronary circulation.

The long-term durability of saphenous vein bypass grafts and their effect on existing intrinsic coronary artery disease remain ill defined. Therefore, sequential catheterization studies were performed in patients selected for study solely on the basis of documentation of a patent graft at an earlier study performed three to nine months postoperatively; at that time 29 patent grafts were demonstrated in 20 patients. Fifteen to 36 months postoperatively (average 22 months), 27 grafts were unchanged, 1 manifested minimal luminal irregularities and 1 was occluded. In one additional patient, studied 4 months and 4 1/2 years postoperatively, the graft was widely patent and had good distal runoff at the second study. Sequential coronary arteriograms revealed that progression of disease to complete occlusion occurred in 24 percent of vessels with severe lesions proximal to a patent graft, whereas progression of disease distal to a graft anastomosis was uncommon. Of 25 vessels not receiving grafts, disease progressed in 5 (20 percent). Grafts that are patent 3 months after operation appear to remain patent for at least 2 to 3 years, and their presence does not unduly accelerate the disease process involving the native coronary arteries.

Adult↗
PubMed1975

Design and function of a mechanical assembly for recording echocardiograms during upright exercise.

It has proved difficult to record satisfactorily echocardiograms during patient motion. This report describes the design and preliminary results obtained with an echo harness with which the transducer can be held stationary or moved rapidly and predictably by remote control. With this apparatus, recordings can be made during tilting, drug intervention, and during bicycle and treadmill exercise.

Amplifiers, Electronic↗
PubMed1975

Operative treatment in hypertrophic subaortic stenosis. Techniques, and the results of pre and postoperative assessments in 83 patients.

The results of operative treatment in 83 patients with idiopathic hypertrophic subaortic stenosis (IHSS) are described. Most patients with the disease are asymptomatic, or derive satisfactory symptomatic improvement from nonoperative therapy: administration of propranolol, exerice limitation, control of arrhythmia, etc. Operation is required, however, in 10-15% of patients, those who remain severely symptomatic after nonoperative treatment or who become refractory to it. Operation relieves symptoms in IHSS by relieving obstruction to left ventricular outflow, and for a patient to be considered an operative candidate severe obstruction must be documented at left heart catheterization either under resting conditions or after provocative interventions. All 83 patients were severely incapacitated--58 in Class III and 24 in Class IV. Seventy had obstruction at rest (average gradient 96 mm Hg), and 13 had only provocable obstruction. At operation the hypertrophic interventricular septum was exposed via an aortotomy, and a vertical bar of muscle was resected between parallel myotomy incisions. There were six operative deaths (7%); no patient has died since 1970. Seven patients have died late after operation, five of them from causes unrelated to their heart disease or the operation. All surviving patients describe symptomatic improvement. Fifty-two patients with obstruction at rest preoperatively (average gradient 95 mm Hg) have been studied postoperatively: no resting gradient was evident in 47, while in the remaining five the gradient was less than 25 mm Hg. Recurrence of obstruction has never been observed at late catheterization (21 pts) or late echocardiographic examination (37 pts). Obstruction could not be provoked postoperatively in ten of the 11 patients who had large gradients only with the Valsalva maneuver or isoproterenol administration preoperatively. Obstructed and provocable obstructed patients had similar symptomatic improvement after operation. A variety of rhythm and conduction abnormalities were observed both pre and postoperatively, and these are described in detail. The results of operation in these 83 patients with IHSS demonstrate that gratifying symptomatic and hemodynamic improvement uniformly follows left ventriculomyotomy and myectomy. Relief of obstruction and amelioration of symptoms have proved to be long-lasting during postoperative observation periods extending to 14 years. Continued application of the operative procedure in properly selected patients appears to be indicated.

Adolescent↗
PubMed1975

Delayed coronary artery dissection after angiography. A case description with successful operative treatment.

A patient is described in whom right coronary artery dissection occurred 48 hours after coronary angiography. Successful operative treatment consisted of immediate saphenous vein bypass grafting and ligation of the proximal coronary artery. Several aspects of the case are characteristic of this pathological entity as reported in the literature and suggest principles of surgical management.

Adult↗
PubMed1975

Atrioventricular valve replacement with the Hancock porcine xenograft: a five year clinical experience.

Since July, 1970, 111 patients have undergone mitral and/or tricuspid valve replacement with a glutaraldehyde-fixed porcine xenograft mounted on a flexible stent; 41 of these patients also had aortic valve replacement with a Starr-Edwards or Bjork-Shiley valve, and 85 patients presently are alive. Cumulative follow-up totals 2,060 months, with 16 patients followed more than 4 years. Anticoagulants have not been administered postoperatively, and one patient has had a systemic embolus. Postoperative hemodynamic assessments have been carried out in 54 patients, and in either the mitral or tricuspid position the valve was shown to have good hydraulic function. Significant mitral regurgitation, secondary to prosthetic dysfunction, occurred in one patient 56 months following implantation. Progressive prosthetic stenosis has not occurred, and hemolysis or anemia of clinical significance has not been observed as a consequence of the use of the use of the xenograft. To date, these clinical and hemodynamic data indicate that the glutaraldehyde-fixed xenograft, mounted on a flexible stent, is the prosthesis of choice for mitral and tricuspid valve replacement.

Aortic Valve↗