Symmetrically biased T/R switches for NMR and MRI with microsecond dead time.

For direct NMR detection and imaging of compounds with very short coherence life times the dead time between radio-frequency (RF) pulse and reception of the free induction decay (FID) is a major limiting factor. It is typically dominated by the transient and recovery times of currently available transmit-receive (T/R) switches and amplification chains. A novel PIN diode-based T/R switch topology is introduced allowing for fast switching by high bias transient currents but nevertheless producing a very low video leakage signal and insertion loss (0.5dB). The low transient spike level in conjunction with the high isolation (75dB) prevent saturation of the preamplifier entirely which consequently does not require time for recovery. Switching between transmission and reception is demonstrated within less than 1µs in bench tests as well as in acquisitions of FIDs and zero echo time (ZTE) images with bandwidths up to 500kHz at 7T. Thereby the 2kW switch exhibited a rise-time of 350ns (10-99%) producing however a total video leakage of below 20mV peak-to-peak and less than -89dBm in-band. The achieved switching time renders the RF pulse itself the dominant contribution to the dead time in which a coherence cannot be observed, thus making pulsed NMR experiments almost time-optimal even for compounds with very short signal life times.

Avoidance of aortic side-clamping for proximal bypass anastomoses: better short-term outcome?

OBJECTIVES: The benefit of off-pump coronary artery bypass (OPCAB) surgery may be reduced by strokes caused by microemboli produced after aortic side-clamping for proximal bypass anastomoses. The Heartstring device allows constructing proximal bypass anastomoses without side-clamping of the aorta. METHODS: This retrospective study describes 260 consecutive patients who underwent OPCAB surgery; 442 proximal anastomoses were performed with the Heartstring device in this series. Ten percent of the patients were randomly sampled before discharge to undergo a coronary angiogram for assessment of graft patency. RESULTS: Intraoperative Doppler measurements confirmed regular bypass function. Early mortality occurred in 4 patients (1.5%), and stroke occurred in 2 patients (0.8%). Device-related bleeding was negligible, and there were no cases of aortic dissection. Perioperative ischemia occurred in 8 patients (3.1%). Predischarge coronary angiography evaluations in 25 of the patients (of 260) showed that all 42 Heartstring-assisted anastomoses (of 442) were patent. CONCLUSIONS: Clampless performance of proximal bypass anastomoses combined with OPCAB is associated with a very low incidence of stroke complications. Short-term follow-up has shown excellent results regarding bypass patency and other adverse events. Prospective randomized trials are required to confirm the advantage of this technique.

Adrenergic receptor genotype but not perioperative bisoprolol therapy may determine cardiovascular outcome in at-risk patients undergoing surgery with spinal block: the Swiss Beta Blocker in Spinal Anesthesia (BBSA) study: a double-blinded, placebo-controlled, multicenter trial with 1-year follow-up.

BACKGROUND: Neuraxial blockade is used as primary anesthetic technique in one third of surgical procedures. The authors tested whether bisoprolol would protect patients at risk for cardiovascular complications undergoing surgery with spinal block. METHODS: The authors performed a double-blinded, placebo-controlled, multicenter trial to compare the effect of bisoprolol with that of placebo on 1-yr composite outcome including cardiovascular mortality, nonfatal myocardial infarction, unstable angina, congestive heart failure, and cerebrovascular insult. Bisoprolol was given orally before and after surgery for a maximum of 10 days. Adrenergic receptor polymorphisms and safety outcome measures of bisoprolol therapy were also determined. RESULTS: A total of 224 patients were enrolled. Spinal block could not be established in 5 patients. One hundred ten patients were assigned to the bisoprolol group, and 109 patients were assigned to the placebo group. The mean duration of treatment was 4.9 days in the bisoprolol group and 5.1 days in the placebo group. Bisoprolol therapy reduced mean heart rate by 10 beats/min. The primary outcome was identical between treatment groups and occurred in 25 patients (22.7%) in the bisoprolol group and 24 patients (22.0%) in the placebo group during the 1-yr follow-up (hazard ratio, 0.97; 95% confidence interval, 0.55-1.69; P = 0.90). However, carriers of at least one Gly allele of the beta1-adrenergic receptor polymorphism Arg389Gly showed a higher number of adverse events than Arg homozygous (32.4% vs. 18.7%; hazard ratio, 1.87; 95% confidence interval, 1.04-3.35; P = 0.04). CONCLUSIONS: Perioperative bisoprolol therapy did not affect cardiovascular outcome in these elderly at-risk patients undergoing surgery with spinal block.

Gene regulatory control of myocardial energy metabolism predicts postoperative cardiac function in patients undergoing off-pump coronary artery bypass graft surgery: inhalational versus intravenous anesthetics.

BACKGROUND: Anesthetic gases modulate gene expression and provide organ protection. This study aimed at identifying myocardial transcriptional phenotypes to predict cardiovascular biomarkers and function in patients undergoing off-pump coronary artery bypass graft surgery. METHODS: In a prospective randomized trial, patients undergoing elective off-pump coronary artery bypass graft surgery were allocated to receive either the anesthetic gas sevoflurane (n = 10) or the intravenous anesthetic propofol (n = 10). Blood samples were collected perioperatively to determine cardiac troponin T, N-terminal pro-brain natriuretic peptide, and pregnancy-associated plasma protein A. Cardiac function was measured with transesophageal echocardiography and pulmonary artery thermodilution. Atrial biopsies were collected at the beginning and end of bypass surgery to determine gene expression profiles. RESULTS: N-terminal pro-brain natriuretic peptide and pregnancy-associated plasma protein A blood levels were decreased with sevoflurane treatment. Echocardiography showed preserved postoperative cardiac function in sevoflurane patients, which paralleled higher cardiac index measurements. N-terminal pro-brain natriuretic peptide release was predicted by sevoflurane-induced transcriptional reduction in fatty acid oxidation, whereas changes in cardiac index were predicted by preoperative gene activity of the peroxisome proliferator-activated receptor gamma coactivator-1alpha pathway. Sevoflurane-mediated attenuation of transcripts involved in DNA-damage signaling and activation of the granulocyte colony-stimulating factor survival pathway predicted improved postoperative cardiac index and diastolic heart function, respectively. CONCLUSIONS: Anesthetic-induced and constitutive gene regulatory control of myocardial substrate metabolism predicts postoperative cardiac function in patients undergoing off-pump coronary artery bypass graft surgery. The authors' analysis further points to novel cardiac survival pathways as potential therapeutic targets in perioperative cardioprotection.

Monitoring activated clotting time for combined heparin and aprotinin application: in vivo evaluation of a new aprotinin-insensitive test using Sonoclot.

OBJECTIVE: Kaolin-based activated clotting time assessed by HEMOCHRON (HkACT) is a clinical standard for heparin monitoring alone and combined with aprotinin during cardiopulmonary bypass (CPB). However, aprotinin is known to prolong not only celite-based but also kaolin-based activated clotting time. Overestimation of activated clotting times implies a potential hazardous risk of subtherapeutic heparin anticoagulation. Recently, a novel 'aprotinin-insensitive' activated clotting time test has been developed for the SONOCLOT analyzer (SaiACT). The aim of our study was to evaluate SaiACT in patients undergoing CPB in presence of heparin and aprotinin. METHODS: Blood samples were taken from 44 elective cardiac surgery patients at the following measurement time points: baseline (T0); before CPB after heparinization (T1 and T2); on CPB, before administration of aprotinin (T3); 15, 30, and 60 min on CPB after administration of aprotinin (T4, T5, and T6); after protamine infusion (T7). On each measurement time point, activated clotting time was assessed with HkACT and SaiACT, both in duplicate. Furthermore, the rate of factor Xa inhibition and antithrombin concentration were measured. Statistical analysis was done using Bland and Altman analysis, Pearson's correlation, and ANOVA with post hoc Bonferroni-Dunn correction. RESULTS: Monitoring anticoagulation with SaiACT showed reliable readings. Compared to the established HkACT, SaiACT values were lower at all measurement time points. On CPB but before administration of aprotinin (T3), SaiACT values (mean+/-SD) were 44+/-118 s lower compared to HkACT. However, the difference between the two measurement techniques increased significantly on CPB after aprotinin administration (T4-T6; 89+/-152 s, P=0.032). Correlation of ACT measurements with anti-Xa activity was unchanged for SaiACT before and after aprotinin administration (r2=0.473 and 0.487, respectively; P=0.794), but was lower for HkACT after aprotinin administration (r2=0.481 and 0.361, respectively; P=0.041). On CPB after administration of aprotinin, 96% of all ACT values were classified as therapeutic by HkACT, but only 86% of all values were classified therapeutic if ACT was determined by SaiACT. Test variability was comparable for SaiACT and HkACT. CONCLUSIONS: The use of SaiACT may result in more consistent heparin management that is less affected by aprotinin and a corresponding increase in heparin administration for patients receiving aprotinin.

Stroke volume and pulse pressure variation for prediction of fluid responsiveness in patients undergoing off-pump coronary artery bypass grafting.

STUDY OBJECTIVES: Stroke volume variation (SVV) and pulse pressure variation (PPV) determined by the PiCCOplus system (Pulsion Medical Systems; Munich, Germany) may be useful dynamic variables in guiding fluid therapy in patients receiving mechanical ventilation. However, with respect to the prediction of volume responsiveness, conflicting results for SVV have been published in cardiac surgery patients. The goal of this study was to reevaluate SVV in predicting volume responsiveness and to compare it with PPV. DESIGN: Prospective nonrandomized clinical investigation. SETTING: University-based cardiac surgery. PATIENTS: Forty patients with preserved left ventricular function undergoing elective off-pump coronary artery bypass grafting. INTERVENTIONS: Volume replacement therapy before surgery. MEASUREMENTS AND RESULTS: Following induction of anesthesia, before and after volume replacement (6% hydroxyethyl starch solution, 10 mL/kg ideal body weight), hemodynamic measurements of stroke volume index (SVI), SVV, PPV, global end-diastolic volume index (GEDVI), central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) were obtained. Also, left ventricular end-diastolic area index (LVEDAI) was assessed by transesophageal echocardiography. Prediction of ventricular performance was tested by calculating the area under the receiver operating characteristic (ROC) curves and by linear regression analysis; p < 0.05 was considered significant. All measured hemodynamic variables except heart rate changed significantly after fluid loading. GEDVI, CVP, PCWP, and LVEDAI increased, whereas SVV and PPV decreased. The best area under the ROC curve (AUC) was found for SVV (AUC = 0.823) and PPV (AUC = 0.808); the AUC for other preload indexes ranged from 0.493 to 0.636. A significant correlation with changes of SVI was observed for SVV (r = 0.606, p < 0.001) and PPV (r = 0.612, p < 0.001) only. SVV and PPV were closely related (r = 0.861, p < 0.001). CONCLUSIONS: In contrast to standard preload indexes, SVV and PPV, comparably, showed a good performance in predicting fluid responsiveness in patients before off-pump coronary artery bypass grafting.