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Biomedical subjects

P T Buser

Publications and source records attributed to P T Buser.

At least 19 recordsLinked to original sources
PubMed2006

The future of cardiovascular imaging and non-invasive diagnosis: a joint statement from the European Association of Echocardiography, the Working Groups on Cardiovascular Magnetic Resonance, Computers in Cardiology, and Nuclear Cardiology, of the European Society of Cardiology, the European Association of Nuclear Medicine, and the Association for European Paediatric Cardiology.

Advances in medical imaging now make it possible to investigate any patient with cardiovascular disease using multiple methods which vary widely in their technical requirements, benefits, limitations, and costs. The appropriate use of alternative tests requires their integration into joint clinical diagnostic services where experts in all methods collaborate. This statement summarises the principles that should guide developments in cardiovascular diagnostic services.

Biomedical Research↗
PubMed2003

Myocardial function and energy metabolism in carnitine-deficient rats.

Carnitine is essential for mitochondrial metabolism of long-chain fatty acids and thus for myocardial energy production. Accordingly, carnitine deficiency can be associated with cardiomyopathy. To better understand this disease, we determined myocardial function and energy metabolism in a rat model of carnitine deficiency. Carnitine deficiency was induced by a 3- or 6-week diet containing N-trimethyl-hydrazine-3-propionate, reducing cardiac and plasma carnitine by 70-85%. Myocardial function was investigated in isolated isovolumic heart preparations. Carnitine-deficient hearts showed left ventricular systolic dysfunction, reduced contractile reserve, and a blunted frequency-force relationship independently of the substrate used (glucose or palmitate). After glycogen depletion, palmitate could not sustain myocardial function. Histology and activities of carnitine palmitoyl transferase, citrate synthase, and cytochrome c oxidase were unaltered. Thus, as little as 3-6 weeks of systemic carnitine deficiency can lead to abnormalities in myocardial function. These abnormalities are masked by endogenous glycogen and are not accompanied by structural alterations of the myocardium or by altered activities of important mitochondrial enzymes.

Adenosine Triphosphate↗
PubMed2001

Long-term outcome of angioplasty for multivessel coronary disease: importance and price of complete revascularization.

BACKGROUND: Complete revascularization of multivessel coronary artery disease (MVD) by coronary artery bypass surgery has been shown to improve outcome, but there is a lack of similar data for patients treated by angioplasty. METHODS: Therefore, a consecutive series of 250 patients with MVD was separated into two groups, those with complete revascularization (n=101) and those with incomplete revascularization (n=149). Six-month 'clinical restenosis' rate assessed by stress myocardial perfusion scintigraphy or symptom-driven angiography and long-term 32 months outcome were compared with an equally sized group of single vessel disease (SVD) patients. RESULTS: MVD patients with complete revascularization had a higher 'clinical restenosis' rate than patients with SVD (35 vs. 22%, P<0.02), although restenosis rate per treated vessel was similar (23%, 18%, P NS). If this higher early restenosis rate were accepted as 'price' for complete MVD angioplasty, long-term event-free survival was no longer different from that of SVD patients (86 vs. 93%, P NS). In contrast, patients with incomplete multivessel angioplasty had a significantly worse long-term outcome (22% events), especially if initially untreated, non-occluded vessels remained untreated (25% events). CONCLUSION: MVD angioplasty with complete revascularization has a long-term event-free survival similar to that of SVD angioplasty but at the price of a higher rate of 6-month restenosis and repeat interventions.

Angioplasty, Balloon, Coronary↗
PubMed2001

Combined blockade of endothelin-1 and thromboxane A(2) receptors against postischaemic contractile dysfunction in rat hearts.

1. Endothelin-1 (ET-1) may play a role in myocardial ischaemia/reperfusion injury because both the release and vasoconstrictor effect of ET-1 are increased after ischaemia. Since the increased vasoconstrictor effect of ET-1 can be mediated by ET-1-induced release of thromboxane A(2) (TXA(2)), the aim of this study was to test whether combined blockade of ET and TXA(2) receptors protects the coronary flow, contractile performance, and cardiac energy metabolism during ischaemia and reperfusion. 2. Bosentan (antagonist for ET(A) and ET(B) receptors, 1 microM based on concentration-response curves of ET-1), SQ 30,741 (antagonist of TXA(2) receptors, 0.1 microM), or the combination thereof was administered to isolated perfused rat hearts undergoing 15 min of global ischaemia and 60 min of reperfusion. 3. Neither bosentan or SQ 30,741 alone, nor the combination thereof, improved the incomplete postischaemic recovery of coronary flow, left ventricular developed pressure, phosphocreatine, or ATP. However, they attenuated ischaemia-induced acidosis but this did not translate into a measurable effect on haemodynamic or metabolic variables. 4. Thus, combined blockade of ET and TXA(2) receptors does not protect the coronary flow, contractile performance, and cardiac energy metabolism during ischaemia and reperfusion in isolated perfused rat hearts. This finding suggests that neither ET-1 nor ET-1-induced release of TXA(2) play a major role in the postischaemic recovery of the cardiac contractile function and energy metabolism.

Adenosine Triphosphate↗
PubMed2001

When calcium turns arrhythmogenic: intracellular calcium handling during the development of hypertrophy and heart failure.

Alterations of intracellular Ca2+ handling in hypertrophied myocardium have been proposed as a mechanism of ventricular tachyarrhythmias, which are a major cause of sudden death in patients with heart failure. In this review, alterations in intracellular Ca2+ handling and Ca2+ handling proteins in the development of myocardial hypertrophy and the transition to heart failure are discussed. The leading question is at what stage of hypertrophy or heart failure Ca2+ handling can turn arrhythmogenic. During the development of myocardial hypertrophy and the transition to failure, Ca2+ handling is progressively altered. Recordings of free myocyte Ca2+ concentrations during a cardiac cycle (Ca2+ transients) are prolonged early in the development of hypertrophy. However, resting (or diastolic) Ca2+ does not increase before end-stage heart failure has developed. These alterations are due to progressively defective Ca2+ uptake into the sarcoplasmic reticulum that seems to be caused by quantitative changes of gene expression of the Ca2+ ATPase of the sarcoplasmic reticulum. Increased expression and activity of the Na+/Ca2+ exchanger might compensate for this defective Ca2+ uptake, probably at the expense of increased arrhythmogenicity. When the Ca2+ handling proteins no longer efficiently counterbalance increasing intracellular Ca2+ - during stress conditions, resulting Ca2+ overload can lead to spontaneous intracellular Ca2+ oscillations, after depolarizations. Thus, after the transition to heart failure, Ca2+ overloaded sarcoplasmic reticulum, increasing resting intracellular Ca2+, and increased Na+/Ca2+ activity may all provoke afterdepolarizations, triggered activity, and finally, life-threatening ventricular arrhythmias. This increased susceptibility to ventricular arrhythmias in heart failure should not be treated with calcium antagonists.

Calcium↗
PubMed2000

Accuracy of biplane analysis of left ventricular ejection fraction based on two consecutive single plane studies.

BACKGROUND AND PURPOSE: Mainly due to the high costs of biplane equipment many cardiac laboratories run single plane angiographic equipment only. Consequently, a biplane ventriculogram may only be done with two consecutive single plane studies. The aim of this investigation was to assess the accuracy of a biplane analysis of two consecutive single plane studies. METHODS: A total of 42 patients (62 +/- 10 years, 76% males), able to tolerate two consecutive ventriculograms without arrhythmia during the first study underwent two consecutive biplane studies (LAO 60, RA0 30), using 40 ml of contrast each. After the first injection, the x-ray tube was moved in a neutral position, and then was replaced in the 30 RAO/60 LAO position. Digital data was analyzed by two separate investigators using commercially available software. RESULTS: Intra-observer variability of left ventricular ejection fraction (LVEF) showed a high degree of agreement (single plane 1 vs. 2: r = 0.98; standard error of regression (Sy.x.): 2.8); the variability was slightly higher with two investigators (single plane: r = 0.92, Sy.x: 5.5 ) and with biplane analysis (biplane 1 vs. 2: r = 0.90, Sy. x: 5.7). End-diastolic volume index (EDVI) increased significantly from the first to the second study (84 +/- 28 ml/m2 vs 87 +/- 30 ml/m2; p = 0.017): Still LVEF of the two consecutive biplane studies showed very good agreement (biplane 1 vs. 2: mean difference (MD), -1.0; standard deviation of the difference (SDD), 5.2%). This agreement was almost as good as the one of LVEF values calculated from two consecutive single plane, but biplane analyzed studies compared to simultaneous biplane studies (MD, -0.5; SDD, 4.3%). CONCLUSION: Despite the significant increase in EDVI after contrast injection, LVEF values determined from two consecutive studies remained virtually unchanged. Biplane analysis of LVEF values based on consecutive single plane studies resulted in similar and reliable values as determined by two consecutive biplane studies.

Angiocardiography↗
PubMed1999

Regional wall motion assessment in stress echocardiography by tissue Doppler bull's-eyes.

Quantification of regional myocardial wall velocities is needed in stress echocardiography for transition from subjective to quantitative assessment. Tissue Doppler allows quantitation of wall velocities, but interpretation is difficult and angle-dependent. Calculating the ratios of velocities with similar angles to the beam may overcome angle dependency. We measured left ventricular wall velocities during stress echocardiography with tissue Doppler. Regional peak systolic and early (E) and late (A) diastolic velocities were constructed in a "bull's-eye" format. Regional stress/rest and E/A ratios were calculated. Bull's-eye map construction demanded only minimal manual interaction, and the maps showed the left ventricular velocity distribution, simplifying wall motion reading markedly. Still, apical velocities appeared lower as a result of Doppler angle-dependency. With velocity ratios, angle-dependency was no longer noted. In stress echocardiography, wall motion abnormalities at rest and contractility changes with dobutamine became readily apparent. Bull's-eye display of quantitative tissue Doppler velocity allows rapid assessment of regional wall motion. Calculating the ratio of regional velocities circumvents the angle-dependency of Doppler. This novel technique has the potential for simplified and automated quantitative analysis in stress echocardiography.

Algorithms↗
PubMed1999

Bradykinin-dependent cardioprotective effects of losartan against ischemia and reperfusion in rat hearts.

It is unclear whether losartan, an angiotensin II type 1 (AT1) receptor antagonist, protects the heart against acute ischemia-reperfusion injury. Therefore we evaluated cardiac protection conferred by pre- and postischemic treatment as well as by exclusive postischemic treatment with losartan. Furthermore, we sought to determine both the extent of this protection and its dependence on bradykinin in comparison with quinaprilat, a cardioprotective angiotensin-converting enzyme inhibitor. Cardiac protection was assessed as recovery of coronary flow, left ventricular developed pressure, phosphocreatine, and adenosine triphosphate (ATP) in isolated perfused rat hearts after 15 min of global ischemia and 30 min of postischemic reperfusion. We found that, in hearts pre- and postischemically treated with losartan (1 microM) or quinaprilat (0.1 microM), these variables all recovered significantly better than those in untreated control hearts. In hearts that were only postischemically treated with losartan, these variables also recovered significantly better than those in control hearts. In contrast, in hearts treated with the combination of the bradykinin B2 receptor antagonist Hoe 140 with quinaprilat or losartan, the recovery of the variables no longer differed from that in control hearts. In conclusion, losartan protects the heart against acute ischemia-reperfusion injury. This protection can be achieved by pre- and postischemic treatment as well as by exclusive postischemic treatment with losartan. Furthermore, the extent of this protection is equivalent to that conferred by quinaprilat and, unexpectedly, dependent on bradykinin.

Adenosine Triphosphate↗
PubMed1998

Ventricular fibrillation-induced intracellular Ca2+ overload causes failed electrical defibrillation and post-shock reinitiation of fibrillation.

Despite high efficacy, electrical defibrillation shocks can fail or ventricular fibrillation (VF) is reinitiated after the application of the initial shock. The goal of this study was to determine whether [Ca2+]i overload, induced by VF itself, can cause failed electrical defibrillation and post-shock reinitiation of VF. For this purpose, we simultaneously measured [Ca2+]i transients (assessed by indo-1 fluorescence) and defibrillation energies (assessed by a modified implantable cardioverter defibrillator) in intact perfused rat hearts during pacing-induced sustained VF (10 min) in the absence of ischemia. We found that increasing [Ca2+]i during VF (by increasing [Ca2+]o from 3 to 6 mM) increased the defibrillation threshold (DFT) from 1.9 +/- 0.6 to 3.5 +/- 0.5 J/g (P<0.05) and also increased the total defibrillation energy (TDE) required for stabilization of sinus rhythm from 15.6 +/- 7.7 to 48.6 +/- 7.42 J/g (P<0.05). In addition, both DFT and TDE correlated linearly with [Ca2+]i (r=0.69 and 0.83, P<0.05). Furthermore, shortening the duration of VF from 10 to 1.5 min tended to limit [Ca2+]i overload and decreased TDE. Finally, all successful defibrillation shocks led to a sudden reduction of VF-induced [Ca2+]i overload (-115 +/- 3%). In contrast, failed shocks did not alter [Ca2+]i. Incomplete reduction of [Ca2+]i overload after initially successful shocks were often followed by synchronized spontaneous [Ca2+]i oscillations and subsequent reinitiation of VF. In conclusion, the present study showed for the first time that VF-induced [Ca2+]i overload can cause failed electrical defibrillation and post-shock reinitiation of VF. Because VF inevitably causes [Ca2+]i overload, this finding might be a crucial mechanism of failed defibrillation and spontaneous reinitiation of VF.

Animals↗
PubMed1997

[Stress echocardiography versus scintigraphy in evaluating coronary heart disease: stress echocardiography is superior].

Stress echocardiography has evolved as a routinely employed non-invasive method for the evaluation of patients with coronary artery disease. The diagnostic accuracy of stress echocardiography for the detection of myocardial ischemia is comparable to scintigraphic myocardial perfusion imaging, and may even have a higher specificity for the evaluation of myocardial viability. User-friendliness including patient and investigator safety, availability and mobility of the method, and environmental compatibility, is superior to that of scintigraphy. The potential for future developments, especially in the field of digital imaging and telecommunication, is great. Last but not least, echocardiography is the method most familiar to cardiologists. The sum of these arguments renders stress echocardiography the superior method to scintigraphy in the evaluation of patients with coronary artery disease.

Coronary Circulation↗
PubMed1997

Prevention of supraventricular tachyarrhythmias after open heart operation by low-dose sotalol: a prospective, double-blind, randomized, placebo-controlled study.

BACKGROUND: The aim of this prospective, double-blind, placebo-controlled trial was to assess the preventive effect and safety of low-dose sotalol after heart operation. METHODS: Two hundred fifty-five consecutive patients referred for elective coronary artery bypass grafting (n = 220) or aortic valve operation (n = 35) were randomized to receive either 80 mg of sotalol twice daily (n = 126) or matching placebo (n = 129) for 3 months, with the first dose given 2 hours before operation. RESULTS: There were no significant baseline differences between the groups. Overall, supraventricular tachyarrhythmias occurred in 36% of patients (82% atrial fibrillation). Hospital stay was 11.6 +/- 5 days in patients with supraventricular arrhythmias, versus 9.5 +/- 2.4 days in patients without it (p < 0.0001). Low-dose sotalol reduced the rate of supraventricular arrhythmias from 46% (placebo) to 26% (sotalol; p = 0.0012), or by 43%. On the fourth postoperative day, heart rate was lower in the sotalol group (74 +/- 12 beats/min versus 85 +/- 15 beats/min; p < 0.0001) but the QT interval corrected for the heart rate was not prolonged (sotalol group, 0.44 +/- 0.03 second; placebo group, 0.43 +/- 0.03 second; p = not significant). Study medication had to be discontinued because of side effects in 5.6% of sotalol and 3.9% of placebo patients (p = not significant), with one possible proarrhythmic event occurring in a patient receiving sotalol. CONCLUSIONS: Because more than 90% of supraventricular arrhythmic episodes occurred within 9 days after operation and 70% of all possibly sotalol related side effects occurred after day 9, the findings in this study imply that prophylactic treatment with sotalol may be limited to the first 9 postoperative days.

Aged↗
PubMed1996

Endothelin-1-induced release of thromboxane A2 increases the vasoconstrictor effect of endothelin-1 in postischemic reperfused rat hearts.

BACKGROUND: The release and vasoconstrictor effect of endothelin-1 (ET-1) are increased after myocardial ischemia, suggesting a role for ET-1 in ischemia/reperfusion injury. However, the mechanisms of the increased vasoconstriction by ET-1 are unknown. The aim of this study was to test whether ET-1-induced release of thromboxane A2 (TXA2) contributes to the vasoconstrictor effect of ET-1 in nonischemic hearts and whether such release can increase the vasoconstrictor effect of ET-1 in postischemic reperfused hearts. METHODS AND RESULTS: ET-1-induced release of TXA2 was assessed by measurement of the concentrations of its stable metabolite thromboxane B2 (TXB2) in the coronary effluent of nonischemic and reperfused isolated rat hearts before and after administration of 0.01 nmol ET-1 using an enzyme immunoassay. The contribution of ET-1-induced release of TXA2 to the vasoconstrictor effect of ET-1 was assessed by measurement of the effects of ET-1 with and without the cyclooxygenase inhibitor indomethacin or the TXA2/endoperoxide receptor antagonist SQ 30,741 using 31P magnetic resonance spectroscopy. In nonischemic hearts, ET-1 led to a small increase in TXB2 in the coronary effluent (3.9 +/- 1.5 pg/mL; n = 3), but neither indomethacin nor SQ 30,741 significantly diminished the vasoconstrictor effects of ET-1 (reduction of coronary flow, 4.0 +/- 0.4 and 4.5 +/- 0.3 mL/min, respectively, versus 4.9 +/- 0.5 mL/min for ET-1 alone; n = 8, 6, and 9, respectively). In postischemic reperfused hearts, however, ET-1 led to a greater increase in TXB2 (13.7 +/- 1.5 pg/mL; P < .05 versus nonischemic hearts; n = 3), and both indomethacin and SQ 30,741 diminished the vasoconstrictor effects of ET-1 (reduction of coronary flow, 2.6 +/- 0.3 and 2.2 +/- 0.3 mL/min, respectively, versus 4.0 +/- 0.1 mL/min for ET-1 alone; n = 8, 8, and 6, respectively; P < .05). Furthermore, indomethacin and SQ 30,741 prevented the detrimental effects of ET-1 on left ventricular developed pressure, intracellular pH, and phosphocreatine during reperfusion. CONCLUSIONS: ET-1-induced release of TXA2 does not significantly contribute to the vasoconstrictor effect of ET-1 in nonischemic hearts but can increase the vasoconstrictor effect of ET-1 in postischemic reperfused hearts.

Adenosine Triphosphate↗
PubMed1996

[Risk stratification following myocardial infarct].

In recent decades, early mortality of acute myocardial infarction has decreased from above 30% to below 10%. Many survivors of acute myocardial infarction are at increased risk for cardiac death and/or nonfatal recurrent ischemic events. This has not changed with the introduction of thrombolysis. How can high risk patients be identified who would benefit from coronary revascularization and/or from antiarrhythmic treatment? Based on clinical findings such as a large infarction, infarction of the anterior wall, congestive heart failure, cardiogenic shock during the acute phase, post-infarct angina and a history of previous infarctions, high risk patients who should undergo coronary angiography and--if feasible--revascularization can be defined. Patients with symptomatic arrhythmias should receive medical or interventional antiarrhythmic treatment. All patients who are clinically considered not to be at high risk should undergo risk stratification with signal averaged ECG, non-invasive stress testing and non-invasive quantification of left ventricular function. In the presence of late potentials, ischemia during stress testing and impaired left ventricular function, further evaluation with Holter ECG or an electrophysiologic study and coronary angiography is indicated. In infarct survivors over 75 years old, the therapeutic goal is improvement of quality of life, i.e. relief of symptoms, rather than improvement of prognosis. Invasive procedures should therefore be considered only in individual patients. However, in all postinfarct survivors the assessment and treatment of cardiovascular risk factors and secondary medical prevention is mandatory.

Adult↗
PubMed1996

[Cerebral ischemic events: when and how to look for a cardiac embolism source?].

In industrialized countries, cerebral ischemic events rank third among the most frequent causes of death. In survivors, long-term disability may result. The diagnosis and therapy of preventable causes is therefore a major task. Echocardiography has proven to be most helpful in the search for cardioembolic sources, and the transesophageal approach (TEE) is superior to the transthoracic (TTE) in this specific indication. In patients in whom a cardioembolic source can be identified by clinical examination, 12-lead surface ECG or chest X-ray, an additional echocardiographic examination is not necessary. Patients under 50 with cerebral ischemic events should undergo TEE. In patients over 70 with a contraindication for long-term anticoagulant therapy, TEE has no therapeutic consequences and should therefore not be performed. In patients aged between 50 and 70 the diagnostic procedure of choice must be considered in each individual patient. It should be kept in mind that a more aggressive approach using TEE, from which therapeutic conclusions are drawn, has not clearly been shown to improve the prognosis of patients with cerebral ischemic events.

Age Factors↗
PubMed1996

[Supraventricular tachycardias: mechanism, diagnosis and therapy].

Most of the paroxysmal forms of supraventricular tachycardia are reentry tachycardias in origin with either an AV-nodal reentry (AVNRT; approx. 50%) or an AV reentry circuit via accessory pathway (AVRT; approx. 30%) as the anatomical basis of tachycardia. The therapeutic options include either drug therapy or transcatheter radiofrequency ablation. In asymptomatic patients, where supra-ventricular tachycardia or WPW syndrome was documented incidentally, an expectative approach without therapy is usually recommended. However, if frequent tachycardia recurrences or severe clinical symptoms (syncope, pre-syncope make treatment mandatory, medical therapy with either betablockers, calcium antagonists or digoxin should be tried if AV-nodal reentry tachycardia is the mechanism (no evidence of WPW syndrome on the 12-lead ECG). In patients with symptomatic WPW syndrome or drug refractory AV-nodal reentry tachycardia, transcatheter radiofrequency ablation with its good results and low complication rate is the therapy of choice. The treatment modality is particularly indicated in young patients who otherwise would need lifelong drug therapy. In contrast, supraventricular tachycardias with badly defined anatomical substrate, such as multifocal atrial tachycardias or atrial fibrillation, should in the first place be treated medically and not by radiofrequency ablation.

Anti-Arrhythmia Agents↗
PubMed1996

[Assessment of ventricular arrhythmias].

In the evaluation of patients with ventricular arrhythmias, those patients with asymptomatic ventricular arrhythmias, who usually comprise a low-risk population, have to be differentiated from patients with symptomatic ventricular arrhythmias (presyncopal symptoms, syncope, cardiac arrest). In general, patients with asymptomatic ventricular arrhythmias should not be treated with antiarrhythmic drugs; however, patients with recent myocardial infarction and asymptomatic ventricular arrhythmias, which may indicate an increased risk of sudden death, should undergo further risk stratification, since some of them might benefit from preventive antiarrhythmic therapy with a beta-blocking agent of amiodarone. In contrast to asymptomatic patients, patients with symptomatic ventricular arrhythmias are at high risk for sudden death, and, if functional status does not mandate against active therapy, these patients should undergo coronary angiography and electrophysiologic evaluation. Revascularization procedures and specific antiarrhythmic measures such as antiarrhythmic drug therapy, ablative therapy (surgical resection or transcatheter radiofrequency ablation of the arrhythmogenic focus) or the implantation of a cardioverterdefibrillator (ICD) are frequently needed in such patients. Consequently, in this high-risk population, early referral to a cardiac center with an electrophysiologic laboratory is recommended, whereas it should be strongly mandated against empirical antiarrhythmic drug therapy.

Adrenergic beta-Antagonists↗