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Biomedical subjects

Thomas Buck

Publications and source records attributed to Thomas Buck.

At least 19 recordsLinked to original sources
PubMed2006

Single-chamber versus dual-chamber implantable cardioverter defibrillators: do we need physiologic pacing in the course?

BACKGROUND: Many patients with ICD receive different antiarrhythmic drugs (e.g. sotalol, amiodarone, beta-blockers) because of ventricular or atrial tachycardias. These drugs can cause AV-block or chronotropic incompetence resulting in a higher percentage of ventricular pacing. METHODS: We analyzed in a retrospective study the impact of DDD(R) versus VVI(R) mode on subjective (NYHA classification) and objective parameters [brain natriuretic peptide (BNP), 6 minute walk test, echocardiography] in 12 of 120 patients (age 60.2 +/- 11.2 years; 10 males, 2 females) who needed an upgrading of a single to a dual chamber ICD. The ICD had to be upgraded because of chronotropic incompetence in all patients with signs of progressing heart failure. Data were collected in VVI(R)-pacing and after 6 and 12 months in DDD(R)-pacing with a long AV-interval and AV hysteresis to reduce ventricular pacing. RESULTS: The 6 minute walk test (392.4 +/- 91.4 vs. 324.6 +/- 93.3 m, P < 0.001), NYHA-classification (1.4 +/- 0.3 vs. 2.6 +/- 0.8, P < 0.0001), BNP (234.1 +/- 73.5 vs. 410.4 +/- 297.0 pg/ml, P < 0.001), left ventricular ejection fraction (49.8 +/- 9.6 vs. 36.5 +/- 10.9 %, P < 0.0001) and A-wave (73.6 +/- 13.7 vs. 41.0 +/- 14.0 cm/sec, P < 0.0001) improved with DDD(R)-pacing after 12 months. The ventricular pacing decreased (84.2 +/- 18.1 vs. 1.1 +/- 1.7 %, P < 0.0001) after 12 months by DDD(R)-pacing with long AV-interval (220.0 +/- 10.4 ms) and AV hysteresis. CONCLUSION: Our data show a superiority of DDD(R) mode versus VVI(R) mode regarding subjective and objective parameters as NYHA-classification, BNP, 6 minute walk test, left ventricular ejection fraction and left ventricular endsystolic volume after 12 months. The improvements seem to depend on the reduction of ventricular pacing with advanced atrial contraction. But only a small number of patients needed the upgradation.

Journal Article↗
PubMed2006

[Current recommendations on echocardiographic evaluation of the severity of mitral regurgitation: standardization and practical application using a scoring system].

Besides diagnosis of the mechanism of mitral regurgitation accurate evaluation of the severity is of critical importance for the assessment of prognosis and planning of therapy. Current recommendations are differentiating two levels of evaluation of severity, (1) a rapid, basic evaluation, and (2) an extended, quantitative evaluation. In the present article the following modified practically applicable system for evaluation and scoring of severity of mitral regurgitation is proposed: step 1: color Doppler jet size: < 4 cm(2) or < 20% of left atrium (LA; = 1 scoring point), 4-8 cm2 or 20-40% of LA (2 points), > 8 cm(2) or > 40% of LA (3 points); step 2: central jet (1 point), eccentric/wall jet (2 points); step 3: LA width: 4 cm (2 points); step 4: proximal jet width: < 0,3 cm (1 point), 0,3-0,7 cm (3 points), > 0,7 cm (5 points). Grades of severity are scored as follows: grade I = 4-5 points, I-II = 6 points, II = 7-8 points, II-III = 9 points, III = 10-12 points. Quantitative Doppler method and PISA (proximal isovelocity surface area) method can be used for calculation of regurgitant volume and effective regurgitant orifice area (EROA), but recommendations for routine application are limited due to indirect measurements and inaccurate hemodynamic assumptions. Special techniques like real-time 3-D echocardiography, quantitative spectral Doppler analysis or stress echocardiographic assessment of severity are still under scientific evaluation. Due to the growing possibilities of early reconstruction of the mitral valve and catheter-based interventional annulus reconstructions, more accurate methods for direct quantification of regurgitant flow will be demanded in the future.

Echocardiography↗
PubMed2006

[Mitral valve prolapse: identification of high-risk patients and therapeutic management].

Mitral valve prolapse shows a wide spectrum from a benign anatomic variant to a progressive disease with severe cardiovascular morbidity and mortality. Echocardiography is the most important tool for diagnosis and risk stratification. Predictors for high risk are significant thickening of mitral leaflet of > 5 mm ("classic" prolapse), moderate to severe mitral regurgitation and reduced left ventricular function. These patients have an increased risk of infective endocarditis, cerebral ischemia and sudden cardiac death. Because of the risk for the development of severe mitral regurgitation requiring surgery short follow-up intervals are necessary. In mitral prolapse syndrome cardiac clinical signs (palpitation, rhythm disorders, syncope, etc.) are associated with a prolapse that can be treated symptomatically with drugs after exclusion of other causes and significant mitral regurgitation requiring surgery.

Humans↗
PubMed2006

[Video-assisted cardiac valve surgery].

BACKGROUND AND PURPOSE: Advances in the development of video-assisted systems for minimally invasive surgery now allow to perform cardiac surgery via a smaller anterolateral thoracotomy in order to reduce trauma, pain and improve cosmetics. In addition, due to sternal sparing, pulmonary function should improve resulting in reduced hospital stay and costs. However, only few centers worldwide abstain from spreading the ribs thus accepting considerable pain and reduced patient comfort. The minimally invasive approach described here uses a right-sided anterolateral incision (4-5 cm), a soft-tissue retractor and femorofemoral perfusion with endoclamping under continuous TEE (transesophageal echocardiography) control. It was the aim of this retrospective analysis to determine feasibility, safety and effectiveness of the method. PATIENTS AND METHODS: At the West German Heart Center Essen, 47 patients were operated using minimally invasive endoscopic techniques between January 2004 and April 2006 on the mitral valve (n = 31), mitral and tricuspid valve (n = 9), including mini-Maze procedure in two cases, as well as atrial septal defects (n = 5) and myxomas (n = 2). Mean age was 58 +/- 15.2 years (range 29-87 years), NYHA II-III, 20 patients were male. RESULTS: All but one patient survived (2.1%). Conversion to median sternotomy was necessary in three of the first twelve patients. After a mean follow-up period of 18 months all reconstructions and valves were competent, freedom from cardiac reoperation was 100%. On a visual analog scale 91% ot the patients reported no or mild postoperative pain, 96% felt they had an aesthetically pleasing scar. All but one patients would choose the same operation again. CONCLUSION: Videoscopically assisted, endoscopic cardiac surgery can be performed safely, but requires a learning curve and intense training. After evaluation of efficacy and safety it is now the authors' exclusive approach to isolated atrioventricular valve disease with an ideal pain-free and cosmetic result.

Adult↗
PubMed2006

[Early single-center experience with the 3F-enable aortic valve bioprosthesis].

BACKGROUND AND PURPOSE: Patients with aortic valve (AV) pathology and severe comorbidities should benefit from reduced myocardial ischemic and extracorporeal circulation (ECC) time. Sutureless implantation of AV prosthesis may reduce myocardial ischemic and ECC time significantly. The authors report on their preliminary results with the first implants of the 3F-Enable sutureless AV prosthesis. MATERIAL AND METHODS: The 3F-Enable prosthesis was implanted in five patients. Prostheses sizes were 27 mm (n = 3), 23 mm (n = 1), and 21 mm (n = 1), respectively. Intraoperatively, at patient's discharge as well as 3 and 6 months postoperatively, the AV prosthesis was evaluated by echocardiography. RESULTS: ECC time was 87 +/- 36 min (range 49-141 min), myocardial ischemic time 55 +/- 27 min (range 32-97 min), and AV implant time 184 +/- 195 s (range 10-420 s). The latest postoperative echo (5.2 +/- 1 months postoperatively) revealed a fully competent AV in three patients, in two patient paravalvular leakage was detected at the severity of an aortic regurgitation (AR) II degrees , and AR II degrees -III degrees , respectively. The mean pressure gradients were 5.8 +/- 1.3 mmHg (range 4.2-7.1 mmHg), valve orifice area was 3.2 +/- 0.4 cm2 (range 2.6-3.6 cm2). CONCLUSION: The first clinical results of the 3F-Enable sutureless AV prosthesis are feasible; however, a paravalvular leakage was detected in two patients (40%). Thus, device and procedural enhancements are required to assure positioning and anchoring of the prosthesis.

Aged↗
PubMed2006

[Change of paradigms in the surgical treatment of complex thoracic aortic disease].

One of the main issues in complex thoracic aortic disease, requiring the replacement of the ascending aorta, the entire aortic arch and the descending aorta, is the vast amount of surgery necessary to cure the patient. Though one-stage repair is feasible by a clamshell thoracotomy, the associated surgical trauma and perioperative morbidity limit this approach to younger patients only. Classic surgical repair consist of a two-stage strategy, whereby, in the first step, the ascending aorta and the aortic arch are replaced via a midline sternotomy. In the second step, via a lateral thoracotomy, the descending aorta is replaced. The two stages may sum up to a mortality of 20%; furthermore, the waiting period between the stages is associated with a mortality rate of 10% of its own. Additionally, the two-stage strategy has an inherent limitation, due to the comorbidity and advanced age of the majority of patients. Therefore, the second stage cannot be offered to up to 30% of patients. New developments and improvements in aortic surgery were introduced to overcome these shortcomings and to simplify the surgical repair. The "elephant trunk" principle, introduced by Borst et al. in 1983, was an important step to facilitate surgical repair, but still required the second step. With the introduction of endovascular repair of thoracic aortic disease with stent grafts implanted retrograde via the femoral artery, new therapeutic concepts emerged. In the late 1990s, two Japanese groups reported first trials to stabilize the free-floating "elephant trunk" prosthesis by implantation of nitinol stent grafts into the vascular graft. The applied devices were purely custom-made and nonstandardized. The availability of industrially made and CE-marked stent-graft devices raised the possibility to apply them in open aortic arch surgery. The experience with stent-graft devices implanted antegrade into the descending aorta (Medtronic Talent) was reported first by the Essen and the Vienna group. The experience gained with these devices revealed the limitations of the devices designed for pure retrograde aortic delivery. This required a complete redesign and new construction of the stent graft itself as well as the introducer system. In a preliminary series of 14 patients the required stent-graft properties were presented in detail and resulted in the first industrially manufactured standardized and CE-marked Hybrid stent graft (Essen 1 prosthesis, E-vita Open, Jotec), especially made for antegrade open stent grafting of the descending aorta. This device consists of a stent graft with an integrated Dacron vascular prosthesis, enabling for direct and continuous aortic arch replacement after stent grafting of the descending aorta. From 01/2005 to 03/2006, this hybrid prosthesis was implanted in 16 patients (one aneurysm and 15 aortic dissections). In all cases, the underlying pathology within the thoracic aspect of the aorta could be excluded in a one-stage approach. In case of aortic dissection, thrombosis of the false lumen was detectable by transesophageal echocardiography already at the end of surgery. Though long-term results using this new method are not yet available, the initial promising results postoperatively are encouraging toward true one-stage repair by combining classic aortic surgery with open antegrade stent grafting utilizing the newly designed hybrid prosthesis. While surgical trauma is markedly reduced, this treatment option can be offered to elderly patients as well.

Adult↗
PubMed2006

Using cardiac magnetic resonance tomography for assessment of aortic valve area in aortic valve stenosis.

Calcified aortic valve stenosis (AS) is the most common valvular disease in the elderly population and constitutes a significant health and socioeconomic problem. Doppler echocardiography is the recommended diagnostic tool for the initial evaluation of AS. Transvalvular pressure gradients and aortic valve area have been used as quantitative parameters for grading the severity of AS, but the latter one is less susceptible to changes in flow dynamics and therefore considered the more independent and reliable parameter. The aortic valve area can be assessed directly by transesophageal echocardiography (TEE), which reflects the anatomic or geometric orifice area, or it can be calculated noninvasively by transthoracic echocardiography (TTE) using the continuity equation, or, invasively, by cardiac catheterization (CC) using the Gorlin formula, both reflecting the effective orifice area. Assessment of aortic valve area by TTE can be limited in some patients due to inadequate acoustic window. Similarly, TEE as a semi-invasive technique is not well tolerated by some patients and the planimetry is limited in patients with heavily calcified aortic valve leaflets. CC is an invasive procedure associated with a substantial risk of cerebral embolism and the Gorlin formula has been shown to be susceptible to changes in flow dynamics. Cardiac magnetic resonance tomography (CMR) is a new imaging technique capable of imaging the aortic valve with high resolution and has recently been used for assessment of the aortic valve area in AS. This review focuses on the feasibility of CMR for the assessment of aortic valve area in AS compared to current standard techniques and discusses some of the typical pitfalls and the sources for the discrepant results observed between the different techniques for assessment of the aortic valve area.

Aortic Valve↗
PubMed2005

Broad-beam spectral Doppler sonification of the vena contracta using matrix-array technology: A new solution for semi-automated quantification of mitral regurgitant flow volume and orifice area.

OBJECTIVES: The objective of this study was to evaluate broad-beam spectral Doppler sonification of the vena contracta using a matrix-array transducer for quantification of mitral regurgitation (MR). BACKGROUND: Noninvasive assessment of the severity of valvular regurgitation remains challenging. A recent technique measures regurgitant flow directly at the vena contracta based on the product of velocity times backscattered Doppler power (proportional to orifice area). That approach, however, has been limited by relatively narrow conventional beamwidths. Matrix-array transducers, recently developed for three-dimensional imaging, can potentially provide broader beams. Therefore, we addressed the hypothesis that deliberate broadening of the Doppler beam can encompass larger regurgitant cross-sectional areas to capture a broader range of regurgitant flows. METHODS: A matrix-array transducer system was modified to provide a three-dimensionally expanded spectral Doppler sample volume. Calculations of orifice area, flow rate, and regurgitant stroke volume (RSV) from Doppler power were automated on board a routinely used echocardiographic scanner and tested in vitro. In 24 patients with isolated MR, RSV was compared with magnetic resonance imaging (MRI) mitral inflow minus aortic outflow from phase-velocity maps. RESULTS: The calculated flow rate and RSV correlated and agreed well with reference values in vitro (r = 0.98 to 0.99) and in patients (r = 0.93, mean difference 0.4 +/- 3.2 ml, p = NS vs. 0), with sufficient sonification to measure flow orifices up to 0.85 cm in diameter. Agreement with MRI was comparable in 17 patients with central and seven with eccentric jets (p = NS vs. 0). CONCLUSIONS: The broad-beam spectral Doppler technique provides accurate, largely automated quantification of regurgitant flow rate and integrated RSV directly at the lesion. The accuracy related to broader sonification is made possible by the new matrix-array transducer design.

Adult↗
PubMed2005

[Echocardiography in the diagnosis of endocarditis: transthoracic or transesophageal?].

Echocardiography is an important tool for diagnosis and risk assessment in patients with infective endocarditis. In addition to the identification of typical vegetations, echocardiography is crucial for the evaluation of valvar regurgitations, and the early diagnosis of complications. Transesophageal echocardiography is, in nearly every aspect, except with concern to right-sided endocarditis, superior to the transthoracic approach. Thus, transesophageal echocardiography represents, in patients with substantial clinical suspicion for an active infection of endocardial structures, the currently most sensitive diagnostic tool.

Echocardiography↗
PubMed2005

[Diagnosis of cardiac disorders by noninvasive techniques in HIV-infected patients].

HIV infection is frequently associated with cardiovascular involvement. Particularly new treatment concepts, including the highly active antiretroviral therapy, are suspected to increase the rate of cardiac and cardiovascular complications in this patient population. Hence, noninvasive techniques such as transthoracic echocardiography and magnetic resonance imaging will become more important in the routine screening as well as in specific diagnostics of cardiovascular involvement of HIV infection. The present article describes the options of these noninvasive techniques for the detection of HIV-associated cardiac manifestations.

Echocardiography↗
PubMed2005

Rapid progression of discrete type A intramural hematoma: prevention of a "procedure-related" complication by intraoperative transesophageal echocardiography.

PURPOSE: To report a case illustrating the utility of transesophageal echocardiography (TEE) before planned stent-graft placement for chronic type B aortic dissection. CASE REPORT: A 64-year-old man with acute aortic syndrome and an 8-year-old interposition graft in the distal aortic arch for acute type B dissection was referred for dissection of the descending thoracic aorta down to the aortic bifurcation; the false lumen was dilated to 65 mm and was partially thrombosed. The ascending aorta showed discrete, eccentric, 4-mm wall thickening that was not considered clinically significant. Stent-graft closure of the entry tear in the proximal descending thoracic aorta was elected. However, as the endovascular procedure was about to commence, TEE showed striking eccentric thickening of the aortic wall of up to 18 mm. The endovascular procedure was stopped, as it was decided to urgently replace the ascending aorta. The next day, the patient underwent successful ascending aortic replacement and simultaneous antegrade stent-graft implantation over the descending thoracic aortic entry tear via the open aortic arch. The postoperative course was uncomplicated, and the patient was discharged 19 days after surgery. He remains well at 6 months after the procedure. CONCLUSIONS: Our case demonstrates that dissection of the ascending aorta may occur not only due to endograft-induced intimal injury, but may also occur due to underlying but undiagnosed or underestimated disease of the ascending aorta or arch. Besides procedural guidance, intraoperative TEE is a useful tool to detect such disease to avoid subsequent "procedure-related" complications.

Aortic Dissection↗
PubMed2003

Analysis of global systolic and diastolic left ventricular performance using volume-time curves by real-time three-dimensional echocardiography.

BACKGROUND: Left ventricular (LV) volume-time curves (VTC) have been described to provide quantitative data on the dynamics of global LV performance beyond ejection fraction. However, generation of VTCs by conventional 2-dimensional imaging techniques is inherently limited because of inaccurate geometric volume assumptions. We, therefore, studied whether the new concept of volumetric scanning as realized by real-time 3-dimensional echocardiography (RT-3DE) can be used to provide accurate VTCs. METHODS: In 30 healthy participants, VTCs were generated from 18 to 24 absolute LV volumes per second by transthoracic RT-3DE and compared with magnetic resonance imaging (MRI) used for reference. LVs were traced manually in 9 to 11 parallel, short-axis planes and volumes calculated by disk method. From VTCs, we determined peak ejection rate (PER), peak early filling rate (PFR), time to PER and PFR, and end-diastolic and end-systolic volumes. For initial clinical application, 2 patient groups of coronary (n = 15) and hypertensive heart disease (n = 16) were studied. RESULTS: In healthy participants, VTCs agreed with MRI (mean errors: PER, -39 +/- 67 mL/s; PFR, -18 +/- 84 mL/s; time to PER, 8 +/- 21 milliseconds; time to PFR 4 +/- 18 milliseconds [not significant vs 0]) whereas VTCs in coronary and hypertensive groups revealed significantly impaired diastolic function. Scanning time for VTCs was only 1 to 2 minutes by RT-3DE and 8 +/- 2 minutes by MRI (P <.001) and time for offline analysis was 22 +/- 5 minutes versus 24 +/- 4 minutes by MRI (not significant). CONCLUSIONS: Generation of VTCs by RT-3DE is feasible and shows excellent agreement with MRI used for reference. Thus, VTCs by RT-3DE is a promising new approach providing access to quantitative information on global LV performance such as LV filling rates that is currently unavailable for the cardiologist.

Adult↗