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Biomedical subjects

T M Sundt

Publications and source records attributed to T M Sundt.

At least 55 records · Page 3Linked to original sources
PubMed1997

The maze procedure for cure of atrial fibrillation.

Atrial fibrillation is the most common dysrhythmia encountered in clinical practice. A significant number of patients fail medical therapy because of inability to convert or control the rhythm pharmacologically, intolerance of the requisite medication, or persistent symptoms despite apparently satisfactory rate control. Based on experimental studies establishing the electrophysiologic basis of atrial fibrillation, a surgical procedure has been developed that is highly effective in restoring sinus rhythm without further requirement for medications. The evolution of this procedure, its current indications, and results are outlined.

Atrial Fibrillation↗
PubMed1997

The surgical management of atrial fibrillation.

Atrial fibrillation is the most common dysrhythmia encountered in clinical practice. For some patients, satisfactory rate control is not possible by pharmacologic means. This led us to develop a surgical approach to its cure, which in turn has led to a deeper understanding of the electrophysiologic basis of atrial fibrillation and to the development of a surgical procedure that is highly effective in restoring sinus rhythm with an acceptable mortality and morbidity. We review these findings as well as the clinical results obtained with the Maze procedure.

Adult↗
PubMed1997

Transmyocardial laser revascularization for inoperable coronary artery disease.

Interest in transmyocardial laser revascularization for the treatment of otherwise inoperable coronary artery disease has increased rather dramatically in recent years. The results of several industrially sponsored clinical series have been reported recently, all with significant improvement in angina pectoris that appears both rapid and sustained. In most instances, an associated improvement in exercise tolerance has been reported. Improvement in regional myocardial perfusion has been proclaimed, although it is less consistent and less complete than symptom relief. The mechanisms whereby this clinical effect is achieved remain unknown. Histologic analysis of autopsy material has yielded somewhat conflicting results regarding the persistent patency of laser-created channels. The results of laboratory investigations of this therapy have been equally inconsistent. Despite our ignorance regarding the mechanism of angina relief, clinical experience continues to grow. In addition to the CO2 laser energy source used in early studies, trials of alternative devices using holmium:yttrium-aluminum-garnet and eximer lasers are underway. The latter two employ fiberoptic technology and are currently under development for endovascular approaches.

Angina Pectoris↗
PubMed1996

Alternative technique for assessment and repair of the mitral valve.

Valve repair is preferred over replacement in the management of mitral regurgitation when technically possible. Central to the achievement of a durable result is precise assessment of the anatomic abnormality present before repair, as well as accurate intraoperative evaluation of the adequacy of repair accomplished. Cardioplegic techniques commonly employed permit inspection of the valve in a flaccid, arrested state, which may not accurately reflect its function in the contractile heart. The repair can be tested under normal loading conditions only after separation from cardiopulmonary bypass. An alternative technique of myocardial management employing mild hypothermia, continuous aortic root perfusion, and intermittent fibrillation is described that provides an opportunity to directly examine the valve under physiologic conditions before, during, and after completion of the repair.

Cardiac Surgical Procedures↗
PubMed1995

Reoperative aortic valve operation after homograft root replacement: surgical options and results.

The surgical options available and the associated operative risks for repeat aortic valve replacement after free-standing homograft root replacement with reimplantation of the coronary arteries are as yet undefined. We therefore reviewed our experience with repeat aortic valve replacement between January 1976 and July 1994 and identified 22 such procedures performed on 21 patients after homograft or autograft root replacement. Reoperation was indicated for structural deterioration in 16 and for bacterial endocarditis in 6 patients. Associated procedures were undertaken in 5 patients, and 4 procedures were performed emergently. Significant calcification of the homograft wall was noted in over half of all patients. There were no coronary ostial complications. In 13 patients new valves were inserted within the previous root: 9 mechanical valves and 4 subcoronary homografts. In 9 patients the root was re-replaced. The mean cross-clamp time was 85 (+/- 20) minutes and mean cardiopulmonary bypass time was 123 (+/- 32) minutes. There were no early deaths and 5 late deaths. Two patients required reoperation for bleeding and 2 experienced low cardiac output syndromes postoperatively. Univariate analysis failed to identify any variables predictive of outcome. We conclude that repeat aortic valve replacement after homograft root replacement, even in the presence of significant calcification, can be undertaken with an acceptable operative risk and should not be delayed until irreversible ventricular dysfunction has occurred. The same options available at initial valve replacement may be employed at reoperation, although extensive calcification mandates repeat root replacement.

Adolescent↗
PubMed1995

Fourteen-year experience with homovital homografts for aortic valve replacement.

Two hundred seventy-five unprocessed, viable homograft ("homovital") aortic valves were used for aortic valve replacement in patients aged 1.5 to 79 years (mean 45.8 +/- 19 years) with maximum follow-up of a 14-year period (mean 4.8 years). Ninety-two percent (252 patients) had New York Heart Association class III or IV functional status before operation and 25 underwent emergency operation. Valves were harvested under sterile conditions and kept in nutrient medium 199. Freehand (subcoronary) technique was used in 147 patients and freestanding root replacement was used in 128. Cumulative survival rates for the whole group were 92% +/- 2% at 5 years and 85% +/- 3% at 10 years, as compared with 96% +/- 2% and 94% +/- 4%, respectively, for the 98 patients who underwent isolated root replacement. Multivariate analysis determined that root replacement with associated procedures and operation for prosthetic endocarditis were risk factors for death, whereas previous xenograft valve, operation for endocarditis, and operation for aortic regurgitation were risk factors for reoperation. Actuarial rates for freedom from degenerative valve failure diagnosed at operation, by postmortem examination, or by routine echocardiography were 94% +/- 2% at 5 years and 89% +/- 3% at 10 years. Recipient age younger than 30 years and previous xenograft valve were risk factors for late degeneration. We conclude that homovital valves demonstrate good durability, particularly in patients older than 30 years, who had a 10-year freedom from degeneration rate of 97%.

Adolescent↗
PubMed1994

Retransplantation in miniature swine. Lack of a requirement for graft adaptation for maintenance of specific renal allograft tolerance.

In miniature swine, one-haplotype class I disparate renal allografts are accepted without exogenous immunosuppression by approximately 35% of recipients. Alternatively, transplants bearing a two-haplotype class I mismatch are always rejected acutely. However, long-term acceptance in the latter animals can be achieved uniformly with a 12-day course of cyclosporine. In vitro studies of recipient cell-mediated lymphocytotoxicity responses have shown donor-specific cytotoxic T lymphocyte clones in tolerant animals, suggesting that tolerance may be a local phenomenon or a central phenomenon activated in the milieu of the graft. Six animals were retransplanted with kidneys MHC-matched to their original allograft to determine whether (1) tolerance is a central phenomenon; (2) host tolerance can be broken with a fresh challenge of donor antigen and antigen-presenting cells; and (3) graft adaptation is required for maintenance of tolerance. Four of the retransplanted animals had been spontaneous acceptors of one-haplotype class I-disparate grafts and two had been rendered tolerant to two-haplotype class I-mismatched kidneys with CsA induction. All six explanted allografts showed no histological evidence of rejection and all six retransplants were accepted without exogenous immunosuppression. These findings suggest that in miniature swine tolerance of class I-disparate kidneys is a stable, centrally mediated phenomenon that cannot be broken with a challenge of fresh donor antigen and donor-type APCs. Furthermore, successful retransplantation without immunosuppression in animals receiving CsA induction therapy for their first transplant suggests that graft adaptation is not necessary for the maintenance of tolerance.

Animals↗
PubMed1994

Angiographically occult vascular malformations: a correlative study of features on magnetic resonance imaging and histological examination.

With reference to vascular malformations, the term cavernous has architectural as well as histologic connotations. It refers to a compact pattern of growth wherein no intervening brain parenchyma is evident, as well as to the histological nature of the vessels, which are hyaline and collagenous in appearance, lacking the microscopic features of arteries or veins. Historically, cavernous angioma has been defined as exhibiting both features. Twenty-five patients with neurological symptoms and neuroimaging abnormalities who underwent surgery for cerebral vascular malformations between 1987 and 1990 satisfied the following study criteria: their lesions were angiographically occult and both magnetic resonance imaging (MRI) and histological sections were available for review. The patients' ages ranged from 4 to 49 years (mean, 30 years), the male to female ratio being 1:2. Two thirds of the lesions were supratentorial in location and all were intraparenchymal. All patients had clinical improvement after resection. In 24 of the 25 lesions, the vascular channels were histologically cavernous in nature; one inadequate specimen precluded classification. Three demonstrated a purely compact or cavernous pattern, 20 a mixed cavernous and racemose pattern, and one a purely racemose pattern. The authors conclude that 1) histologically cavernous lesions are the commonest form of occult vascular malformation; 2) a purely compact or cavernous architectural pattern is uncommon, most lesions showing a partially racemose architecture; 3) some histologically cavernous malformations possess a capillary component; 4) clinical growth of cavernous malformations may have its basis in intraluminal thrombosis and subsequent recanalization; 5) the T2-weighted MRI pattern of cavernous malformations varies, the most common being a multifocal hyperintense center surrounded by a hypointense ring; 6) the MRI pattern reflects the histological appearance; 7) since no thrombosed arteriovenous malformations were encountered, such lesions must be rare; 8) in that the pathophysiological hallmark of a cavernous lesion is recurrent thrombosis and hemorrhage, a resolving hematoma cannot always be distinguished from a cavernous lesion; 9) MRI is the examination of choice in evaluating occult vascular malformations; and 10) microsurgical excision is a satisfactory method of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1994

Retirement of Mrs. Jean Lawe, managing editor of the Journal of Neurosurgery.

On June 30, Mrs. Jean Lawe will step down as Managing Editor of the Journal of Neurosurgery. She has worked on the Journal since 1965, when Dr. Louise Eisenhardt retired as the first Editor. Since that time the Journal has grown in size and circulation, and production has become fully computerized. In her valedictory, Mrs. Lawe summarizes her years with the Journal and her approach to scientific editing.

History, 20th Century↗
PubMed1993

Extensive allelic polymorphism in the CDR2-like region of the miniature swine CD4 molecule.

MHC class II polymorphism is well documented whereas only minimal polymorphism has been reported for the CD4 molecule with which it interacts. We report on the structural basis of an allelic polymorphism of the CD4 molecule in miniature swine. Eleven of 13 nucleotide differences between the 2 alleles cause amino acid replacements. A majority of these replacements are clustered in a region protruding as a loop structure, termed Ig CDR2-like, from the surface of the amino terminal domain. This part of the human CD4 appears to comprise the binding site for the human immunodeficiency virus gp120 protein. The loop structure has also been implicated in the binding of CD4 to MHC class II, but this is currently a matter of some controversy. Our previous results have indicated that the porcine CD4 polymorphism, that we now show is situated in this loop, does not significantly affect the binding to class II. However, because the polymorphism appears to have been selected for and is situated in a very exposed part of the molecule, it is likely to be of functional significance.

Alleles↗
PubMed1993

Renal dysfunction and intravascular coagulation with aprotinin and hypothermic circulatory arrest.

High-dose aprotinin was used in 20 patients undergoing primary or repeat operations on the thoracic or thoracoabdominal aorta using cardiopulmonary bypass and hypothermic circulatory arrest. The activated clotting times immediately before the establishment of hypothermic circulatory arrest exceeded 700 seconds in all but 1 patient. Three patients (15%) required reoperation for bleeding. Seven patients died during hospitalization, and 5 had postmortem examination. Platelet-fibrin thrombi were present in multiple organs including the coronary arteries of 4 patients with myocardial infarction or failure, the pulmonary arteries of 2 patients, 1 of whom died of acute right ventricular failure, the brains of 2 patients who sustained a stroke, and the kidneys of 4 patients, 3 of whom had development of renal dysfunction. Renal dysfunction occurred in 13 patients (65%), and all were 65 years of age or older. Five of these patients required hemodialysis. Among 20 age-matched patients who had similar operations without aprotinin, there was one hospital death (5%) from myocardial infarction, and renal dysfunction developed in 1 patient (5%), who did not require dialysis. None of these 20 patients required reoperation for bleeding. Although aprotinin has been shown to reduce blood loss in patients having cardiac operations employing cardiopulmonary bypass, this benefit was not attained in this group of patients with thoracic aortic disease in whom hypothermic circulatory arrest was used. Use of aprotinin in elderly patients undergoing these procedures was associated with an increased risk of renal dysfunction and failure, and of myocardial infarction and death.

Aged↗
PubMed1993

Transitional cavernous aneurysms of the internal carotid artery.

Twenty-three cases of transitional cavernous aneurysms are presented. Aneurysms of this subgroup (of a total of 118 cases of cavernous sinus aneurysms) arise entirely from within the cavernous sinus but project into the extracavernous intradural subarachnoid space, thus resembling other intracranial aneurysms in their increased risk of rupture. Six aneurysms were small (less than 15 mm), 6 were large (15 to 25 mm), and 11 were giant (more than 25 mm). Thirteen patients (57%) had a subarachnoid hemorrhage, nine patients (39%) had compressive symptoms, and one patient (4%) was asymptomatic. A direct surgical approach was performed successfully in 18 cases (78%), and indirect bypass methods were performed in 5 cases. The overall surgical outcome was excellent in 87% of the patients, with three complications (13%) including one fatality. It is suggested that this subgroup is a different entity from other cavernous or extracavernous aneurysms and should be managed aggressively with direct clipping whenever possible because of the increased risk of subarachnoid hemorrhage. A simplified numerical classification system of clinoidal-region aneurysms of the internal carotid artery (including transitional aneurysms) is also proposed.

Adult↗
PubMed1993

Seizure outcome in patients with surgically treated cerebral arteriovenous malformations.

A series of 280 cases of cerebral arteriovenous malformations (AVM's) treated surgically between June, 1970, and June, 1989, is reviewed with particular focus on the preoperative seizure history and follow-up seizure status. Follow-up evaluation (mean duration 7.5 years) was achieved in 98% of cases and was accomplished through re-examinations, telephone interviews, and written questionnaires. Overall, 89% of the surviving patients with a follow-up period of greater than 2 years were free of seizures at last examination. Of the 280 patients in this series, 163 had experienced no seizures preoperatively. A recent follow-up study (with a minimum duration of 2 years or to death) was available in 157 of these 163 cases; 21 patients had died. Of the 136 surviving patients, only eight (6%) were having new ongoing seizures. In the 128 (94%) who had remained seizure-free, 73% were receiving no anticonvulsant agents while 27% were taking anticonvulsant prophylaxis. The 2-year minimum follow-up study in 110 of the 117 patients with preoperative seizures revealed that eight (7%) had died. Of the 102 surviving patients, 85 (83%) were seizure-free (with 48% no longer receiving anticonvulsant therapy), while 17 (17%) still suffered intermittent seizures. However, of these 17 patients, 13 reported their seizures to be improved compared to preoperatively; the seizures were the same in two patients and were worse in two patients. An actuarial analysis was conducted comparing the life expectancy of patients following surgery for AVM's with the expected survival of a general white population of the same age and sex in the West Northcentral region of the United States. No statistically significant difference was found. There were seven perioperative deaths (three from cerebral hemorrhage, two from pulmonary emboli, and two from obstruction of venous drainage) and 22 deaths during the follow-up period. Of these 22 deaths, the cause was unknown in four patients, apparently unrelated to the AVM in 13, and directly or indirectly related to the patient's neurological condition prior to surgery or due to surgery performed for resection of the AVM in five. There was a statistically significant relationship between the size and location of the AVM and the clinical presentation. Patients with small AVM's (< 3 cm) were more likely to present with hemorrhage whereas those with large AVM's were more likely to present with seizures.(ABSTRACT TRUNCATED AT 400 WORDS)

Actuarial Analysis↗
PubMed1993

Occlusive hyperemia: a theory for the hemodynamic complications following resection of intracerebral arteriovenous malformations.

An alternative theory is proposed to explain the brain edema and hemorrhage that may occur after resection of high-flow intracerebral arteriovenous malformations (AVM's). This theory, termed "occlusive hyperemia," is based on a retrospective analysis of operative dictations along with postoperative imaging studies (191 angiograms and 273 computerized tomography scans) in 295 cases of intracerebral AVM's operated on at the Mayo Clinic between 1970 and 1990. In this series, 34 cases (12%) of postoperative deterioration were documented, of which 15 were due to incomplete resection of the AVM. Of the remaining 19 cases, six had brain edema alone and 13 had hemorrhage with edema, despite complete excision of the AVM. In these 19 cases, the AVM's were greater than 6 cm in diameter in 10 patients, between 3 and 6 cm in six, and less than 3 cm in three. Obstruction of the venous drainage system was observed in 14 (74%) of the 19 cases. Ten of these 14 were due to obstruction of the primary venous drainage of the brain parenchyma immediately surrounding the lesions, while four were due to obstruction of other venous structures. In no case was a rapid circulation identified on postoperative angiograms. The flow pattern was slow or stagnant in former AVM feeders and their parenchymal branches. It is proposed that postoperative intracranial hemorrhage and/or brain edema in AVM patients may be due to: 1) obstruction of the venous outflow system of brain adjacent to the AVM, with subsequent passive hyperemia and engorgement; and 2) stagnant arterial flow in former AVM feeders and their parenchymal branches, with subsequent worsening of the existing hypoperfusion, ischemia, and hemorrhage or edema into these areas. Supportive hemodynamic evidence for this theory was derived from the literature.

Adult↗
PubMed1993

Referral bias in aneurysmal subarachnoid hemorrhage.

The objective of this study was to assess the effect of referral bias on survival in patients with subarachnoid hemorrhage (SAH). The characteristics of 49 patients with aneurysmal SAH from a single community were compared with those of 328 patients referred from outside the community, all treated in the same medical care setting. In addition, referral patients who received surgery were compared by differential survival analysis with those still awaiting surgery at Days 1 to 3, Days 4 to 10, and Days 11 to 15. There was a dramatic difference in the 30-day survival rate between referral patients (83%) and community patients (59%), but most of the difference had occurred by the 2nd day after SAH. In the referral patients, the variables present at first medical attention that were found to have an independent effect on survival were clinical grade, presence of coma, number of days from SAH to referral, diastolic blood pressure, and patient age. There was a higher survival rate at 1 year for patients who were surgically treated compared with those awaiting surgery for each of the three time periods. Patients who underwent early surgical treatment had a 1-year survival rate almost identical to that of patients with late surgery. Referral patients had a better early survival rate than did community patients because the referral group did not include patients who died and some who were in poor clinical condition before the opportunity for referral. The differential survival analysis described provides a new method for estimating survival for treated and untreated patients with SAH.

Adolescent↗
PubMed1993

Arteriovenous fistulas of the brain and the spinal cord.

Arteriovenous (AV) fistulas of cerebral and spinal arteries are characterized angiographically by an immediate AV transition without a capillary bed or "nidus" as occurs in AV malformations (AVM's). The clinical presentation, morphology, radiology, and treatment of 12 patients with cerebral AV fistulas and of 12 patients with spinal AV fistulas are reviewed. In the patients with cerebral lesions, headache and seizure disorders were the most common presentations followed by subarachnoid hemorrhage, cardiac failure, progressive neurological dysfunction, and incidental detection on prenatal ultrasound study. In patients with spinal AV fistulas, weakness and sensory disturbance in the lower extremities were the most frequent clinical presentations followed by back pain, disturbances of micturition, and grand mal seizure. The etiology of the symptom complex produced by AV fistulas in each of these locations differed, with venous hypertension being important in spinal cord lesions. Of the patients with cerebral lesions, nine had a single AV fistula, one had two fistulas, and two had multiple fistulas. An AVM was observed in five patients with fistulas (two large, three small). Nine patients exhibited extramedullary AV fistulas of the spine, of whom eight had a single fistula and one had three fistulas; three patients had intramedullary spinal AV fistulas. An arterial aneurysm was found in association with two fistulas, one cerebral and one spinal. Venous ectasias or varices, frequently exhibiting mural calcification, were observed to be prominent in all AV fistulas involving cerebral arteries and in two involving spinal arteries. The location and size of the venous complexes reflected the diameter of the fistula. In addition to conventional imaging techniques (cerebral angiography, computerized tomography, and magnetic resonance (MR) imaging), MR angiography was a helpful adjunct in the evaluation of fistulas. Treatment strategies employed for AV fistulas in both locations included open surgical and endovascular procedures, frequently used in combination. A satisfactory outcome was observed in all patients.

Adolescent↗