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Biomedical subjects

Thomas Walther

Publications and source records attributed to Thomas Walther.

At least 91 records · Page 5Linked to original sources
PubMed2004

Changes of blood pressure and heart rate variability precede a grand mal seizure in a pregnant woman.

In order to evaluate blood pressure and heart rate variability as a potent diagnostic tool for different hypertensive pregnancy disorders we started a clinical trial recording these variables in early pregnancies predisposed for preeclampsia. During routine measurements one of the patients experienced a grand mal epileptic seizure. Since the parameters of both heart rate and blood pressure variability were sequentially altered immediately before the seizure, this case report provides an interesting insight into autonomic cardiovascular control in a developing convulsive fit and the pathophysiological generation of a grand mal seizure in pregnancy.

Adult↗
PubMed2004

Restitution of sinus rhythm plus stentless mitral valve replacement at three years.

BACKGROUND AND AIM OF THE STUDY: The study aim was to examine results after stentless mitral valve (SMV) replacement (Quattro) and restitution of physiological cardiac rhythm by intraoperative left atrial ablation therapy. METHODS: Twenty patients (13 females; mean age 69.7 +/- 5.9 years) with severe degenerative mitral valve disease (six with valve stenosis, six with valve incompetence, eight with combined lesion) were prospectively evaluated since 1998. The mean NYHA functional class was 3.2 +/- 0.4, and cardiac index 1.8 +/- 0.5 l/min/m2. Ablation therapy was performed by inducing left atrial linear lesion lines to avoid reentrant circuits. RESULTS: Surgery was performed using conventional sternotomy (n = 10) or lateral minithoractomy (n = 10). Sinus rhythm was successfully restituted in 17 patients either postoperatively or in the long term (success rate 85%). However, three patients required DDD-pacemaker implantation, and another three had to be discharged with persistent atrial fibrillation. Intermittent medical therapy (sotalol or amiodarone) was required in nine patients postoperatively, in four patients at six months, and in two patients at one-year follow up. One patient was reoperated on for paravalvular leak after one year, but subsequently died due to sepsis. In the other patients, echocardiographic control proved good SMV function with atrial contraction. CONCLUSION: Restitution of physiological cardiac function is possible by combined stentless MV implantation and left atrial ablation therapy. A persistent benefit, without need for additional re-intervention, was shown at mid-term follow up.

Aged↗
PubMed2004

Early results with stentless mitral valve replacement.

BACKGROUND AND AIM OF THE STUDY: Implantation of a chordally supported stentless mitral valve (SMV) may be the strategy of choice for patients with severe degenerative mitral valve disease. Herein, the early clinical results of this surgical technique were analyzed. METHODS: Since August 1997, 52 patients (36 females, 16 males; mean age 68.0 +/- 8.5 years) each received a SMV (Quattro; St. Jude Medical Inc.) at the authors' institution. The underlying disease was predominant mitral stenosis (n = 26), incompetence (n = 17) and combined lesion (n = 9). The mean NYHA class was 3.1 +/- 0.6, left ventricular ejection fraction 64 +/-13%, and cardiac index 2.1 +/- 0.8 1/min/m2. RESULTS: SMV implantation was performed using either a conventional sternotomy (n = 33) or a lateral minithoracotomy (n = 19). The mean implanted valve size was 29.2 +/- 1.7 mm, and mean cross-clamp time 81 +/- 33 min. Reoperation was required in six patients: two for paravalvular leakage, two for functional stenosis (both 26 mm valves), in one patient for pannus formation with underlying collagenosis, and in one for papillary flap rupture at five years. One patient died perioperatively, one died after reoperation at one year, and five patients died at longer follow up, from non-cardiac causes. Hemodynamic function was shown to be normal on echocardiography. CONCLUSION: Intermediate-term results after SMV implantation were promising. Preservation of annuloventricular continuity led to good left ventricular function, but long-term durability remains to be proven.

Aged↗
PubMed2003

Fibrosis rather than blood pressure determines cardiac BNP expression in mice.

BACKGROUND: Since first reports demonstrated interactions between the natriuretic peptide (NPS) and renin-angiotensin system (RAS), our experiments should clarify whether cardiac brain natriuretic peptide (BNP) is regulated in mice genetically altered for components of the RAS. METHODS AND RESULTS: The study was carried out in hypotensive AT1- and angiotensinogen (ANG)-, and normotensive AT2-knockout mice, and in hypertensive animals overexpressing ANG and wildtype controls of each genotype. Ventricular BNP expression was analyzed by RNase-protection assay (RPA) (n=6). Cardiac fibrosis was visualized by Sirius red staining. While ANG overexpression increases cardiac BNP-mRNA expression (1035+/-210 vs. wildtype: 405+/-95 in PSL/mm(2), P<0.01), its deficiency had no influence. Both AT1- and AT2-knockouts showed significantly decreased BNP-mRNA concentrations (AT1: 21+/-6 vs. wildtype: 139+/-28 in PSL/mm(2), P<0.001; AT2: 8+/-2 vs. 19+/-3 in PSL/mm(2), P<0.05). These alterations correlate to reduced cardiac fibrosis in AT2-deficient animals, and an unchanged matrix content in ANG knockouts. CONCLUSIONS: Increased BNP-mRNA levels in hypertensive ANG-overexpressing mice and decreased BNP in hypotensive AT1-deficient animals suggest that this mRNA expression is blood pressure-dependent. However, the observed alterations of fibrosis and the unchanged BNP in hypotensive ANG knockouts and impaired BNP-mRNA expression in normotensive AT2-deficient mice demonstrate a direct interaction of the RAS and NPS that is fibrosis- rather than blood pressure-dependent.

Animals↗
PubMed2003

Predictors of prolonged ICU stay after on-pump versus off-pump coronary artery bypass grafting.

OBJECTIVE: To define predictors for prolonged ICU stay in order to improve patient outcome and reduce costs. PATIENTS AND METHODS: Prospective data on 10,759 patients undergoing coronary artery bypass grafting with and without use of cardiopulmonary bypass (coronary artery bypass grafting, CABG; n =8,917; off-pump coronary artery bypass grafting, OPCAB; n =765; minimally invasive direct coronary artery bypass grafting, MIDCAB; n =1,077) between April 1996 and August 2001 were subjected to univariate and, consecutively, to multivariate logistic regression analysis. Prolonged ICU stay was defined as intensive care treatment for three postoperative days and longer. MEASUREMENTS AND RESULTS: Mean duration of ICU stay was 3.8+/-6.9 days; overall prevalence of prolonged ICU stay was 37.1%. The hospital mortality was 3.5% (ICU > or =3 days: 5.9%; ICU <3 days: 2.0%). Out of 39 selected pre- and intraoperative patient- and treatment-related variables, by univariate analysis, 32 variables having a high association with prolonged ICU stay were identified. Using a stepwise logistic regression model, 20 variables were shown to be independent predictors for prolonged ICU stay. Both OPCAB and MIDCAB surgery were identified as having a significantly lower association with prolonged ICU stay. CONCLUSION: As prolonged ICU stay is associated with poor patient outcome and increased costs it is of utmost importance to identify patients at a high risk for prolonged ICU stay. More frequent off-pump CABG may optimize patient outcome.

Aged↗
PubMed2003

Midterm results after stentless mitral valve replacement.

BACKGROUND: To analyze the midterm clinical results after stentless mitral valve (SMV) replacement. METHODS AND RESULTS: Fifty one patients (68.3+/-8.4 years, 35 female) with severe mitral valve disease (stenosis 25, incompetence 17, mixed lesion 9) received a chordally supported SMV (Quattro, St. Jude Medical Inc.) since August 1997. Preoperative New York Heart Association class was 3.1+/-0.6; left ventricular ejection fraction 64+/-13%, and cardiac index 2.1+/-0.8 l/min/m2. Additional intraoperative ablation therapy was performed on 19 patients with chronic atrial fibrillation. Mean follow-up is 35.4+/-19.2 months (range 5 to 63). SMV implantation was performed using a conventional (32) or a minimally invasive (19) approach, valve size was 29+/-1.5 mm, cross-clamp duration was 81+/-33 minutes. Atrial rhythm was reestablished in 16 of 19 patients. Five patients required reoperation early in this series, two for paravalvular leakage, two for functional stenosis, and one with underlying rheumatoid disease. Mortality was one perioperative (1.96%, non-valve-related), one after reoperation as a result of multiple organ failure (MOF), and five during late follow-up (30+/-7 months postoperatively) for noncardiac causes. Regular echocardiographic control revealed good SMV function (Vmax 1.7+/-0.2m/s, P(mean) 3.9+/-1.2 mm Hg) and well-preserved ejection fraction postoperatively and at most recent follow-up. CONCLUSIONS: Midterm results after SMV implantation are promising. Preservation of the annuloventricular continuity leads to stable left ventricular function and combined with ablation therapy to physiological hemodynamics. Long-term durability remains to be proven.

Aged↗
PubMed2003

Angiotensin-(1-7) is an endogenous ligand for the G protein-coupled receptor Mas.

The renin-angiotensin system plays a critical role in blood pressure control and body fluid and electrolyte homeostasis. Besides angiotensin (Ang) II, other Ang peptides, such as Ang III [Ang-(2-8)], Ang IV [Ang-(3-8)], and Ang-(1-7) may also have important biological activities. Ang-(1-7) has become an angiotensin of interest in the past few years, because its cardiovascular and baroreflex actions counteract those of Ang II. Unique angiotensin-binding sites specific for this heptapeptide and studies with a selective Ang-(1-7) antagonist indicated the existence of a distinct Ang-(1-7) receptor. We demonstrate that genetic deletion of the G protein-coupled receptor encoded by the Mas protooncogene abolishes the binding of Ang-(1-7) to mouse kidneys. Accordingly, Mas-deficient mice completely lack the antidiuretic action of Ang-(1-7) after an acute water load. Ang-(1-7) binds to Mas-transfected cells and elicits arachidonic acid release. Furthermore, Mas-deficient aortas lose their Ang-(1-7)-induced relaxation response. Collectively, these findings identify Mas as a functional receptor for Ang-(1-7) and provide a clear molecular basis for the physiological actions of this biologically active peptide.

Angiotensin I↗
PubMed2003

Transgenic rat model of Huntington's disease.

Huntington's disease (HD) is a late manifesting neurodegenerative disorder in humans caused by an expansion of a CAG trinucleotide repeat of more than 39 units in a gene of unknown function. Several mouse models have been reported which show rapid progression of a phenotype leading to death within 3-5 months (transgenic models) resembling the rare juvenile course of HD (Westphal variant) or which do not present with any symptoms (knock-in mice). Owing to the small size of the brain, mice are not suitable for repetitive in vivo imaging studies. Also, rapid progression of the disease in the transgenic models limits their usefulness for neurotransplantation. We therefore generated a rat model transgenic of HD, which carries a truncated huntingtin cDNA fragment with 51 CAG repeats under control of the native rat huntingtin promoter. This is the first transgenic rat model of a neurodegenerative disorder of the brain. These rats exhibit adult-onset neurological phenotypes with reduced anxiety, cognitive impairments, and slowly progressive motor dysfunction as well as typical histopathological alterations in the form of neuronal nuclear inclusions in the brain. As in HD patients, in vivo imaging demonstrates striatal shrinkage in magnetic resonance images and a reduced brain glucose metabolism in high-resolution fluor-deoxy-glucose positron emission tomography studies. This model allows longitudinal in vivo imaging studies and is therefore ideally suited for the evaluation of novel therapeutic approaches such as neurotransplantation.

Animals↗
PubMed2003

Stroke after cardiac surgery: a risk factor analysis of 16,184 consecutive adult patients.

BACKGROUND: Stroke remains a devastating complication after cardiac surgical procedures despite advances in perioperative monitoring and management. The purpose of this study was to determine the predictors of stroke in a large, contemporary cardiac surgery population. METHODS: Prospective data on 16,184 consecutive patients undergoing cardiac surgery (coronary artery bypass grafting [CABG], n = 8,917; beating heart CABG, n = 1,842; aortic valve surgery, n = 1,830; mitral valve surgery, n = 708; double or triple valve surgery, n = 381; CABG and valve surgery, n = 2,506) between April 1996 and August 2001 were subjected to univariate and multivariate analysis. Stroke was defined as any new permanent (manifest stroke) or temporary neurologic deficit or deterioration (transient ischemic attack or prolonged reversible ischemic neurologic deficit) and was confirmed by computed tomography or magnetic resonance imaging whenever possible. RESULTS: Overall incidence of stroke was 4.6% and varied between surgical procedures (CABG 3.8%; beating-heart CABG 1.9%; aortic valve surgery 4.8%; mitral valve surgery 8.8%; double or triple valve surgery 9.7%; CABG and valve surgery 7.4%). Of 63 patient-specific and treatment variables, 54 were found to have a significant univariate association with postoperative stroke. Multivariable analysis revealed 10 variables that were independent predictors of stroke: history of cerebrovascular disease, peripheral vascular disease, diabetes, hypertension, previous cardiac surgery, preoperative infection, urgent operation, CPB time more than 2 hours, need for intraoperative hemofiltration, and high transfusion requirement. Beating heart CABG was associated with a lower incidence of stroke in this multivariable analysis. CONCLUSIONS: Identification of predictors for stroke is important for understanding the pathogenesis of this devastating complication as well as for developing preventative strategies. Although retrospective analyses can be subject to selection bias we believe beating heart CABG is associated with a lower incidence of stroke and may therefore improve patient outcomes.

Adult↗
PubMed2003

Secundum ASD closure using a right lateral minithoracotomy: five-year experience in 122 patients.

BACKGROUND: Surgical closure of secundum atrial septal defect (ASD) is a standard procedure associated with very low mortality and morbidity. We evaluated outcomes in the era of catheter-based interventional closure and minimally invasive techniques. METHODS: From May 1996, February 2002, 177 patients with a body weight of more than 30 kg underwent surgical ASD closure. A right lateral minithoracotomy (LMT) was used in 122 patients and a conventional approach, in 55. Diagnoses included secundum ASD in 106 patients in the LMT group and 40 in the conventional group, sinus venosus ASD in 13 patients in each group, and status post interventional closure in 3 and 2 patients, respectively. Mean age was 37 +/- 17 years in the LMT group and 43 +/- 20 years, in the conventional group and mean body weight was 66 +/- 17 kg and 70 +/- 16 kg, respectively. In the LMT group, femoral cannulation was performed for cardiopulmonary bypass. RESULTS: Direct ASD closure was carried out in 67.2% of patients in the LMT group and 58.2% of those in the conventional group. The remaining patients had pericardial patch closure. There was one death: A patient in the conventional group who required explantation of an Amplatzer device because of infection died postoperatively. Average stay in the intensive care unit was 1.2 +/- 0.5 days. Two patients required reoperation for residual ASD after direct closure; 1 sustained a temporary neurological deficit that resolved completely. On postoperative echocardiography, a minimal residual shunt was seen in only 3 patients. All patients were in good clinical condition with improved functional status at discharge from the hospital. CONCLUSIONS: Secundum ASD closure by LMT has become as standard and safe an operation as the conventional technique and achieves good perioperative results and satisfactory long-term outcomes. Thus LMT is an attractive option for patients who are not suitable for closure using catheter-based devices.

Adolescent↗
PubMed2003

Successful treatment for intraoperatively evolving acute aortic dissection in a neonate.

Acute aortic dissection is a life-threatening condition. We report the case of a neonatal one-stage correction of coarctation and hypoplastic aortic arch repair plus ventricular septal defect closure. While dissecting the head vessels after cannulation of the ascending aorta and commencing cardiopulmonary bypass, type A aortic dissection evolved. This required immediate ascending aorta and aortic arch reconstruction with coarctation of the aorta resection under hypothermic circulatory arrest. The surgical management of this rather unique situation is discussed here.

Acute Disease↗
PubMed2003

Intraoperative left atrial ablation (for atrial fibrillation) using a new argon cryocatheter: early clinical experience.

PURPOSE: Recently surgical treatment of atrial fibrillation has gained more popularity and presently is being performed in large numbers of patients. This report describes our early experience in treatment of patients with chronic or paroxysmal atrial fibrillation with a new tool for left atrial cryoablation. DESCRIPTION: From July 2002 through January 2003, 28 patients underwent left atrial cryoablation with the Surgifrost CryoCath. Patients underwent cryotherapy as an isolated procedure (n = 1), in combination with mitral valve surgery (n = 13), or with other surgical procedures (n = 14). In all patients contiguous lesion lines to the orifices of the pulmonary veins connected to the mitral annulus and the atriotomy were created. Surgery was performed through a conventional sternotomy in 8 patients (29%) and a right lateral minithoracotomy using video-assistance in 20 patients (71%). EVALUATION: Postoperatively sinus rhythm was restored in 27 patients (96%). At discharge 82% (23/28) of patients were in sinus rhythm and 18% (5/28) were in atrial fibrillation. Four patients (14%) required pacemaker implantation. There was no in-hospital mortality. At 6-months follow-up (19/28 patients) all were alive and 74% were in stable sinus rhythm, New York Heart Association functional class was 1.2 +/- 0.4. CONCLUSIONS: As indicated by our small and early patient cohort left atrial cryoablation with the Surgifrost argon cryocatheter is effective for the treatment of atrial fibrillation. This new device is technically easy to handle, it can be applied through a median sternotomy or lateral minithoracotomy. Long-term follow-up is necessary to evaluate further rhythm outcome.

Adult↗
PubMed2003

Limitations for manual and telemanipulator-assisted motion tracking--implications for endoscopic beating-heart surgery.

BACKGROUND: Surgical performance is limited by human factors. Beating-heart surgery requires full dexterity and motion tracking. Currently techniques for total endoscopic beating-heart bypass grafting using telemanipulation systems are being developed. The aim of this study was to assess the limitations for manual and telemanipulator-assisted motion tracking using the da Vinci telemanipulator system. METHODS: To simulate beating-heart conditions an endoscopic trainer was developed. Twenty subjects were asked to touch targets manually and with telemanipulator assistance with different patterns of increasing index of difficulty (resting model, unstabilized, and stabilized model with a frequency of 35, 60, and 90 beats per minute). In addition one task was performed using different scaling ratios on a resting model. The times between hits as well as errors were electronically recorded. RESULTS: There was no significant impact of various frequencies and amplitudes for manual tracking. The average values for the delay (k(m)[ms]) and information-processing (c(m) [ms/bit]) constants for the manual tasks were 201 ms and 86 ms/bit respectively. Both the delay constant (k(t) = 630 ms; p < 0.0005) and the information-processing constant (c(t) = 250 ms/bit; p < 0.0005) were increased for the telemanipulator-assisted tasks at rest. When working on moving targets telemanipulator-assisted tracking required significantly more time and led to more errors. At a frequency of 90 beats per minute telemanipulator-assisted tracking became more difficult. CONCLUSIONS: Endoscopic beating-heart bypass grafting requires optimal stabilization to avoid inaccuracies due to incomplete motion tracking. At higher frequencies telemanipulator-assisted tracking became more difficult, demonstrating the technical limits of current telemanipulator technology.

Cardiac Surgical Procedures↗
PubMed2003

Facilitated endoscopic beating heart coronary artery bypass grafting using a magnetic coupling device.

BACKGROUND: Suturing of a coronary anastomosis in totally endoscopic coronary artery bypass grafting on the beating heart is technically demanding. The potential benefits of the endoscopic Magnetic Vascular Positioner device (Ventrica, Inc, Fremont, Calif) to facilitate construction of a coronary anastomosis in a closed chest environment were evaluated. METHODS: Totally endoscopic coronary artery bypass grafting on the beating heart was performed in 8 foxhound-beagle inbred dogs with the da Vinci telemanipulation system (Intuitive Surgical, Mountain View, Calif). A prototype of the endoscopic Magnetic Vascular Positioner device was used to facilitate construction of the coronary anastomosis. One pair of magnets was inserted in the internal thoracic artery and left anterior descending artery using robotic instruments to guide and place the endoscopic delivery platform. All animals underwent angiography; gross inspection of the anastomotic site was performed after excision of the hearts. RESULTS: The procedure was accomplished in all animals in 169 minutes (155-190 minutes). Dissection of the left anterior descending coronary artery (6.5 minutes; 1-20 minutes), positioning of the stabilizer (8.5 minutes; 7-16 minutes), placement of occlusion tapes (6 minutes, 3-10 minutes), and arteriotomy 5.5 minutes (3-30 minutes) was achieved without problems. By use of the Magnetic Vascular Positioner device, the anastomosis at the graft site was performed with the graft still in situ. Except for 1 premature deployment, all other deployments were easily accomplished in 3 minutes (1-28 minutes). The following adverse events were encountered: bleeding from the right ventricle caused by occlusion tape (1), anastomotic leakage on reperfusion requiring repair stitches (2), and anastomotic occlusion as a result of thrombus (1). All except 1 animal with a patent graft and anastomosis survived the procedure. The overall patency was 7 of 8. DISCUSSION: The combination of robotic technology allowing for dexterous manipulation in a closed chest environment and a simple yet effective and timesaving technique for anastomotic coupling may facilitate beating heart totally endoscopic coronary artery bypass grafting.

Anastomosis, Surgical↗
PubMed2003

Robotic coronary artery bypass grafting (CABG)--the Leipzig experience.

Technical and anatomical limitations as well as human factors complicate endoscopic coronary bypass surgery. Computer-enhanced telemanipulation systems overcome some of these shortcomings by restoring the dexterity and precision of a distant operator (surgeon) within a confined space. Endoscopic coronary artery bypass grafting (CABG) has evolved from a merely experimental approach to a clinical concept. Although CABG was initially exclusively performed on the arrested heart, adjunct technologies such as endoscopic vacuum-assisted stabilizers now allow a closed-chest, beating-heart procedure. The development of anastomotic devices, and further refinements in telemanipulator technology, optical systems, and image-guided augmented-reality scenarios will greatly facilitate endoscopic bypass grafting in the future.

Coronary Artery Bypass↗
PubMed2003

Closure of recurrent VSD due to dehiscence of calcified patch.

Closure of residual ventricular septal defects may be extremely difficult in the presence of severe calcification of a previous patch. Removal of such calcification carries a risk of damaging the aortic and tricuspid valve as well as the conduction system. We describe a novel technique for closure of such a defect placing a new patch over and around the calcified one in an 18-year-old patient who had undergone initial surgery 12 years ago.

Adolescent↗
PubMed2003

Mitral valve repair in patients with end stage cardiomyopathy: who benefits?

OBJECTIVE: Patients with end stage cardiomyopathy frequently present with additional severe mitral regurgitation. We analyzed the outcome of mitral valve reconstruction in this high risk patient group. METHODS: Sixty-six patients with significant mitral regurgitation and an ejection fraction (EF) below 30% (dilated cardiomyopathy=53, ischemic cardiomyopathy (ICM)=13) were retrospectively evaluated from 07/96 and 02/02. All received annuloplasty ring implantation and additional repair (n=4) if required. Mean follow-up was 28+/-18 months. RESULTS: Mitral valve repair (MVR) was technically feasible in all patients. Intraoperative transesophageal echocardiography (TEE) revealed none (n=60) or only trivial (n=6) residual mitral regurgitation. Thirty day mortality was 6.1%. Actuarial survival after 1 and 5 years was 86+/-4 and 66+/-8%, respectively. During follow-up seven patients were transplanted due to lack of clinical improvement after 10+/-7 months (range 1-23). Echocardiography revealed a significant improvement in EF (25+/-10.5% pre-op, 34+/-15% post-op) and a slight decrease in left ventricular end-diastolic diameter (69+/-10 mm pre-op, 67+/-13 mm follow up). Patients were in NYHA functional -class 3 (median) preoperatively and in class 2 at long term-follow-up. Gender, left ventricular enddiastolic diameter, preoperative ejection fraction or type of surgical approach (sternotomy, right lateral minithoracotomy) had no significant influence on patient outcome. Patients with ICM or patients older than 60 years showed an increased risk for clinical events both early post-operatively and at long-term follow-up. CONCLUSION: MVR can be performed with low perioperative morbidity and mortality even in patients with advanced heart failure, modifying selection criteria for potential candidates may further improve long term outcome.

Adult↗