Clinical experiences with the use of ULTRAPRO® mesh in single-stage direct-to-implant immediate postmastectomy breast reconstruction in 102 patients: A retrospective cohort study.

BACKGROUND: Acellular dermal matrices have been used for direct-to-implant (DTI) breast reconstruction (BR), eliminating the load of the lower pole skin envelope. However, the available allograft matrices add considerable health care costs. This study examined the long-term follow-up of synthetic ULTRAPRO® mesh as a low-cost potential alternative to biological matrices. PATIENTS AND METHODS: A retrospective cohort study was performed between January 2013 and January 2016, involved 112 early-stage breast cancer and/or BRCA 1/2 patients, and evaluated 189 immediate DTI BRs following skin-, areola- or nipple-sparing mastectomy using ULTRAPRO® mesh. Patient characteristics and postoperative complications were recorded, and quality of life was rated by the patients using the EORTC-QLQ-C30-BR23 questionnaire. Aesthetic outcomes and palpability of the implants were evaluated by four breast surgeons on a 5-point Likert scale. All recorded parameters were statistically analysed. RESULTS: Ten patients were lost-to-follow-up, resulting in 102 patients and 174 breast surgery cases analysed. The mean age was 43 years, with 23.4 months of follow-up on average. Forty-six patients (45.1%) had previous radiotherapy with pre-existing scars. In total, 32 complications (18.3%) were recorded, including 12 minor (6.9%) and 20 major (11.4%) complications requiring revision. All median quality of life scores were above 83 points, representing a high score, with an average 4-point rating for the aesthetic outcome and natural consistency of the breast. CONCLUSION: Partially absorbable ULTRAPRO® mesh could be used successfully in DTI BR, offering a safe, less expensive alternative to biological matrices. Adequate indications and patient selection are necessary.

Objective decision making between conventional and oncoplastic breast-conserving surgery or mastectomy: An aesthetic and functional prospective cohort study.

BACKGROUND: Breast-conserving surgery (BCS) is considered the standard treatment for early-stage breast cancer. However, fair to poor cosmetic outcomes following conventional BCS have been observed in as many as one-third of cases. The aim of this study was to determine the critical tumor-to-breast volume ratio for each quadrant of the breast beyond which conventional BCS would no longer offer acceptable cosmetic and functional results or satisfactory quality of life for the patient. METHODS: A prospective cohort study was performed between December 2011 and December 2013 involving 350 patients younger than 70 years with early-stage unifocal (T ≤ 30 mm) breast cancer who underwent wide excision and axillary sentinel lymph node biopsy followed by whole-breast irradiation. Using validated panels and software (the Breast Cancer Treatment Outcome Scale [BCTOS], EORTC Cancer Quality of Life Questionnaire number C30-BR23, and Breast Cancer Conservative Treatment - cosmetic results [BCCT.core] software), quality of life and aesthetic and functional parameters and their changes in correlation to the percentage of breast volume excised were statistically analyzed. RESULTS: The maximum percentages of breast volume that were resectable by conventional BCS without resulting in unacceptable aesthetic and functional outcomes or decreased quality of life were 18-19% in the upper-outer quadrant (p < 0.0001), 14-15% in the lower-outer quadrant (p < 0.0001), 8-9% in the upper-inner quadrant (p < 0.0001), and 9-10% in the lower-inner quadrant (p < 0.0001). CONCLUSION: Aided by the calculated cut-off values for each breast quadrant, breast surgeons might render more objective decisions regarding performing conventional BCS, using oncoplastic techniques or choosing mastectomy with immediate reconstruction.

Does breast screening offer a survival benefit? A retrospective comparative study of oncological outcomes of screen-detected and symptomatic early stage breast cancer cases.

INTRODUCTION: Mammography screening reduces breast cancer mortality by up to 32%. However, some recent studies have questioned the impact of non-palpable breast cancer detection on mortality reduction. The aim of this study was to analyse the clinicopathological and long-term follow-up data of early stage screened and symptomatic breast cancer patients. PATIENTS AND METHOD: The institutional prospectively led database was systematically analysed for breast cancer cases diagnosed via the mammography screening program from 2002 to 2009. As a control group, symptomatic early stage breast cancer patients were collected randomly from the same database and matched for age and follow-up period. All medical records were reviewed retrospectively. RESULTS: Data from 298 breast cancer patients were collected from 47,718 mammography screenings. In addition, 331 symptomatic breast cancer patients were randomly selected. The screened group presented a significantly lower median tumour size (P < 0.00001). The incidence of negative regional lymph nodes was significantly higher in the screened group (P < 0.0006). The incidence of chemotherapy was 17% higher in the symptomatic group (P = 4*10-5). At the median follow-up of 65 and 80 months, the screened group did not exhibit better overall (P = 0.717) or disease-free survival (P = 0.081) compared to the symptomatic group. CONCLUSION: Our results do not suggest that mammography screening does not reduce breast cancer mortality but the mammography screening did not bring any significant improvement in patient overall or disease-free survival for the early stage breast cancer patients compared to the symptomatic group. The drawback of symptomatic early stage tumours compared to non-palpable tumours could be equalized by modern multimodality oncology treatments.

A novel catheter system for totally implantable intravenous drug therapy: assessment of catheter function and patency with trepostinil therapy.

BACKGROUND: Catheter failure, either due to dislodgment, occlusion or infection is the leading complication of chronic intravenous drug therapy. Better drug delivery techniques are required to advance life saving therapies that require this delivery method. This study evaluated the chronic performance of a fully implantable drug delivery system that incorporates a novel intravenous catheter. The system was designed to reduce complications associated with intravascular drug delivery including catheter occlusion, breakage, migration, and infection. METHODS: Twelve canines were implanted with a novel central venous catheter (Model 10642; Medtronic, Minneapolis, MN) connected to a totally implanted programmable drug pump (Model 8637 SynchroMed II, Medtronic). The drug delivery systems infused saline (n=6) or treprostinil (n=6) (Remodulin; United Therapeutics, Research Triangle Park, NC) for either 12 or 26 weeks at a continuous flow rate of 540 microL/day. Catheter performance was assessed at 0 (implant), 2, 4, 8, 12, 16, 20, and 24 weeks by quantifying delivery pressure, delivery volume and steady state Treprostinil concentrations. RESULTS: All catheters remained patent and free of complications for the duration of the study. Analysis of pressure waveforms during bolus delivery showed low and unchanged catheter resistance throughout the study. Measurement of pump delivery volume accuracy showed that the delivered volume was statistically similar to the calculated delivery (product of flow rate and elapsed time). Measurement of plasma treprostinil levels showed stable concentrations over the study period. There were no catheter dislodgments or breakage. Pathology showed all catheters free from fibrosis and thrombus and minimal changes to the vascular endothelium. CONCLUSIONS: The Model 10642 vascular catheter along with the SynchroMed II implantable drug delivery system showed promising performance in a chronic animal model.

Defibrillation energy requirements and electrical heterogeneity during total body hypothermia.

OBJECTIVE: Determine the effects of hypothermia on defibrillation energy requirements and cardiac electrophysiology. DESIGN: Prospective randomized acute intervention trial. SETTING: Medical center animal laboratory. SUBJECTS: Fifteen domestic farm swine. INTERVENTIONS: Swine were randomized to a hypothermia group (n = 8) or a control group (n = 7). All animals were instrumented with a transvenous defibrillation system connected to a defibrillator that delivers a biphasic-truncated waveform. Values for defibrillation energy requirements were measured at baseline (normothermia, 38-40 degrees C) and during treatment with total body hypothermia (30 degrees C) or no temperature change (sham). Hypothermia was induced by circulating ice-water through anterior and posterior surgical thermal blankets. MEASUREMENTS AND MAIN RESULTS: Defibrillation energy requirement values at 20%, 50%, and 80% were determined by using an up/down method. In the hypothermia group, defibrillation energy requirement values at baseline did not significantly change during hypothermia (defibrillation energy requirements 50% = 14 +/- 2 J vs. 15 +/- 2 J, respectively). Similarly, the defibrillation energy requirement values in the control group did not change from baseline to sham phase (defibrillation energy requirements 50% = 12 +/- 1 J vs. 13 +/- 1 J, respectively). Hypothermia profoundly affected cardiac electrophysiology, decreasing ventricular fibrillation threshold by 72%, conduction velocity by 25% (p < .01), and tissue excitability, while it prolonged ventricular repolarization and refractoriness by 7.5% to 15%, respectively (p < .05). CONCLUSIONS: Total body cooling to 30 degrees C was highly arrhythmogenic, although this unstable electrophysiological state did not alter ventricular defibrillation energy requirements. These data suggest that hypothermia may be used to slow metabolic processes without concern over the ability to successfully defibrillate and treat hypothermia-induced arrhythmias.

Enhanced endothelin-1 response and receptor expression in small mesenteric arteries of insulin-resistant rats.

Hyperinsulinemia, a primary feature of insulin resistance, is associated with increased endothelin-1 (ET-1) activity. This study determined the vascular response to ET-1 and receptor binding characteristics in small mesenteric arteries of insulin-resistant (IR) rats. Rats were randomized to control (C) (n = 32) or IR (n = 32) groups. The response to ET-1 was assessed (in vitro) in arteries with (Endo+) and without (Endo-) endothelium. In addition, arteries (Endo+) were pretreated with the ET(B) antagonist A-192621 or the ET(A) antagonist A-127722. Finally, binding characteristics of [(125)I]ET-1 were determined. Results showed that in Endo+ arteries the maximal relaxation (E(max)) to ET-1 was similar between C and IR groups; however, the concentration at 50% of maximum relaxation (EC(50)) was decreased in IR arteries. In Endo- arteries, the E(max) to ET-1 was enhanced in both groups. Pretreatment with A-192621 enhanced the E(max) and EC(50) to ET-1 in both groups. In contrast, A-127722 inhibited the ET-1 response in all arteries in a concentration-dependent manner; however, a greater ET-1 response was seen at each concentration in IR arteries. Maximal binding of [(125)I]ET-1 was increased in IR versus C arteries although the dissociation constant values were similar. In conclusion, we found the vasoconstrictor response to ET-1 is enhanced in IR arteries due to an enhanced expression of ET receptors and underlying endothelial dysfunction.

Lidocaine increases the proarrhythmic effects of monophasic but not biphasic shocks.

INTRODUCTION: Lidocaine increases monophasic shock defibrillation energy requirement (DER) values but does not alter biphasic shock DER values. However, the mechanism of this drug/shock waveform interaction is unknown. It may be that lidocaine increases the proarrhythmic actions of monophasic shocks but not biphasic shocks. Thus, lidocaine may increase monophasic shock DER values by increasing myocardial vulnerability to shock-induced ventricular fibrillation. METHODS AND RESULTS: Area of myocardial vulnerability (AOV), defined by a two-dimensional grid according to shock strength (y-axis) and shock coupling interval (x-axis), was assessed for biphasic shocks (n = 11) and monophasic shocks (n = 13) in intact swine hearts. Shocks were randomly delivered during right ventricular pacing at 10 shock strengths (50 to 500 V) and five coupling intervals (160 to 240 msec). AOV was defined as the number of points within the test grid that induced ventricular fibrillation. AOV, upper limit of vulnerability (ULV), and DER values were determined at baseline and during systemic infusion of lidocaine (10 mg/kg/hour). Lidocaine increased AOV, ULV, and DER values by 35%, 23%, and 36%, respectively, for monophasic shocks. However, lidocaine did not alter AOV, ULV, or DER values for biphasic shocks. CONCLUSION: Lidocaine increases the AOV to monophasic shocks, which is directly related to changes in ULV and DER values. This implies that lidocaine increases the proarrhythmic activity of monophasic shocks but not biphasic shocks. This may explain why lidocaine increases monophasic shock DER values.

Comparison of the pharmacokinetics and in vivo bioaffinity of DigiTAb versus Digibind.

The in vivo digoxin binding affinity and normal pharmacokinetic values of digoxin-immune Fab are unknown. Healthy subjects (n = 16) were randomized to one of the two digoxin-immune Fab products, DigiTAb or Digibind, to compare the in vivo digoxin binding affinity and pharmacokinetic disposition. Each subject received 1 mg of intravenous digoxin infused during 5 minutes followed 2 hours later by 76 mg of either DigiTAb or Digibind. Both Fab products reduced free digoxin serum concentrations to below assay detection with equal ability. Consequently, total digoxin serum concentrations increased approximately 10-fold. Peak total digoxin serum concentrations post-Fab dosing were similar to the pre-Fab peak digoxin concentration for both Fab products (45 +/- 14 and 44 +/- 11 for DigiTAb, pre and post, respectively) 50 +/- 17 and 41 +/- 9 for Digibind, pre and post, respectively) indicating in vivo equimolar binding affinity. While bioaffinity for digoxin was equal between groups, total digoxin area under the curve (AUC) and digoxin-immune Fab AUC were lower in the DigiTAb group compared with the Digibind group. Hence, systemic total digoxin and Fab clearance were greater in the DigiTAb-treated group. In conclusion, equimolar doses of both DigiTAb and Digibind completely bind digoxin in vivo. The ability of digoxinimmune Fab to bind to digoxin is not affected by the systemic disposition of the Fab product.

Cytochrome P450 activity and endothelial dysfunction in insulin resistance.

Impaired endothelium-dependent relaxation attributable to nitric oxide/prostacyclin-independent factor (endothelium-dependent hyperpolarizing factor; EDHF) has been demonstrated in the small mesenteric arteries of insulin-resistant rats. The purpose of this study was to determine if modulation of the cytochrome P450 enzyme system would restore EDHF-mediated relaxation in insulin-resistant rats. Sprague-Dawley rats were randomized to control (n = 32) or insulin-resistant (n = 32) groups. Each group was further randomized to treatment (n = 48) or placebo (n = 16). Miconazole (3 days) and phenobarbital (3 and 14 days) achieved cytochrome P450 inhibition and induction, respectively. Following drug treatment, mean arterial pressure was measured and vascular function was assessed in small mesenteric arteries in vitro. Specifically, acetylcholine-induced relaxation alone and in the presence of indomethacin plus N-nitro-L-arginine (LNNA) or KCl was determined. Miconazole reduced the maximal relaxation in response to acetylcholine in control rats. Similarly, in the presence of LNNA plus indomethacin, acetylcholine-induced relaxation was impaired in the miconazole-treated control group versus the placebo group, whereas relaxation in the presence of KCl was unchanged. Miconazole did not affect relaxation in insulin-resistant arteries. In contrast, 3- and 14-day treatment with phenobarbital significantly improved acetylcholine-induced relaxation in insulin-resistant arteries. Likewise, acetylcholine-mediated relaxation in the presence of LNNA plus indomethacin was also improved after phenobarbital treatment, while relaxation in the presence of KCl was unchanged. Phenobarbital treatment did not affect the control group. Miconazole treatment increased the mean arterial pressure in control rats, while 14-day phenobarbital treatment normalized the mean arterial pressure in insulin-resistant rats. Cytochrome P450 induction results in the restoration of EDHF-mediated relaxation in small mesenteric arteries and the normalization of mean arterial pressure in insulin-resistant rats. Thus, endothelial dysfunction secondary to insulin resistance can be reversed by the induction of cytochrome P450.

Observations on the behavior of gibbons (Hylobates leucogenys, H. gabriellae, and H. lar) in the presence of mirrors.

Three captive gibbons (Hylobates leucogenys, H. gabriellae, and H. lar) were videotaped in the course of longitudinal exposure to mirrors introduced into their familiar cage or island housing situation. The gibbons, which differed in age, sex, species, and rearing condition, exhibited great individual differences in their behavioral reactions to mirrors, spanning from a minimal reaction dominated by social responses to a dramatic sequence of progressive behavioral change that featured a variety of contingency testing behaviors and included mirror-mediated, self-directed behavior. Additional information on the mirror competence of gibbons was provided by modified mark tests and a hidden object task. The results are discussed in relation to current criteria for self-recognition in primates and factors involved in individual and species differences in reactions to mirror exposure.

Endotoxemia alters splanchnic capacitance.

The splanchnic circulation constitutes a major portion of the total capacitance vasculature and may affect venous return and subsequently cardiac output during low output states. This study assessed the effects of rapid (10 microg/kg over 5 min) and slow (10 microg/kg over 60 min) induction of endotoxin (Escherichia coli) shock on splanchnic blood volume in 8 farm swine. Blood volume was measured by using Tc99m-labeled erythrocytes and radionuclide imaging. Baseline arterial pressure (MAP), central venous pressure (CVP), and liver, splenic, mesenteric and total splanchnic volumes were stable during the 30-min baseline. Approximately 30 min after the rapid endotoxin infusion, splenic volume decreased by 45%, whereas liver volume increased by 40% and MAP decreased by 60% (P < 0.01). The reduction in splenic volume occurred within 10 min of the endotoxin infusion, whereas liver volume changes occurred after MAP reduction. The slow endotoxin infusion also reduced splenic volume by approximately 50% (P = 0.05), whereas MAP declined by 30% (P < 0.05). However, the slow endotoxin infusion lowered liver volume (P < 0.05). Mesenteric volume was unaffected by the fast or slow endotoxin infusion. Total splanchnic volume was unaffected by the fast infusion but decreased by 37% in the slow infusion group (P < 0.05). In summary, E. coli endotoxin reduces splenic blood volume and increases liver blood volume after acute hypotension ensues. Endotoxin does not increase total splanchnic blood volume and may actually decrease total splanchnic volume in the absence of circulatory collapse. This endotoxin shock model is not associated with blood volume pooling in the splanchnic capacitance circulation.

Regional hyperkalemia increases ventricular defibrillation energy requirements: role of electrical heterogeneity in defibrillation.

INTRODUCTION: Increased spatial electrical heterogeneity has been associated with impaired defibrillation efficacy. The current study investigated the relationship between electrical heterogeneity and defibrillation efficacy by manipulating spatial electrical heterogeneity. METHODS AND RESULTS: We increased spatial electrical heterogeneity by infusing potassium chloride (2 to 4 mEq/hour) or placebo in the left anterior descending artery in 13 pentobarbital anesthetized swine. Electrophysiologic measurements at five myocardial sites and defibrillation energy requirement (DER) values were determined at baseline and during regional hyperkalemia (n = 7) or placebo (n = 6). Regional potassium infusion was titrated to a 20% reduction in action potential duration in the perfused region. Regional hyperkalemia increased biphasic DER values by 87% (P = 0.02), whereas infusion of placebo did not alter defibrillation efficacy. Regional hyperkalemia decreased myocardial repolarization and refractoriness in the perfused region by 21% (P < 0.001) and 18% (P = 0.01), respectively. However, regional hyperkalemia increased ventricular fibrillation cycle length (VFCL) by 39% (P = 0.008). Consequently, dispersions of repolarization, refractoriness, and VFCL were significantly increased by 169%, 92%, and 200%, respectively. Regional hyperkalemia also increased ventricular conduction time to the perfused region by 54% (P = 0.006), indicating conduction velocity dispersion, while not affecting local pacing threshold or local voltage gradient. CONCLUSION: Regional hyperkalemia increased DER values. Regional hyperkalemia likely impairs defibrillation by increasing myocardial electrical heterogeneity, which supports the theory that electrical heterogeneity promotes nonuniform propagation of early postshock activations, thereby inhibiting defibrillation.

Metformin improves vascular function in insulin-resistant rats.

This study assessed the effect of metformin treatment on insulin, mean arterial pressure (MAP), and endothelial function in insulin-resistant (IR) rats. In addition, we assessed the direct effect of metformin in vitro. Sprague-Dawley rats were randomized to control (n=28) or IR (n=28) groups. Rats were further randomized to receive metformin (300 mg/kg) or placebo for 2 weeks. MAP and insulin were measured. Subsequently, a third-order branch of the superior mesenteric artery was isolated, and endothelial function was assessed. Specifically, dose-response experiments of acetylcholine (ACh) with or without N-nitro-L-arginine (LNNA) were performed. For in vitro experiments, mesenteric arteries were removed from untreated control and IR rats and treated with metformin (100 micromol/L) before ACh+/-LNNA. MAP and insulin levels were improved in IR-metformin compared with IR-placebo rats. Maximal relaxation (E(max)) to ACh was enhanced in IR-metformin (92+/-2%) compared with IR-placebo rats (44+/-4%) (P<0.05). Relaxation in response to ACh+LNNA was greater in IR-metformin (33+/-4%) than in IR-placebo rats (12+/-4%) but remained depressed compared with control rats (E(max)=68+/-5%). The control group was not affected by metformin. In vitro treatment of arteries with metformin in response to ACh produced results similar to those in the experiments with metformin-treated rats. Although metformin improves metabolic abnormality in IR rats, this action does not appear to mediate its effect on vascular function. Both in vivo and in vitro metformin improved ACh-induced relaxation in IR rats to control levels, apparently through nitric oxide-dependent relaxation. These data suggest that metformin improves vascular function through a direct mechanism rather than by improving metabolic abnormalities.

Induction of electrical heterogeneity impairs ventricular defibrillation: an effect specific to regional conduction velocity slowing.

BACKGROUND: This study determined whether dispersion of conduction velocity, refractoriness, or excitability increases biphasic shock defibrillation energy requirements (DERs). METHODS AND RESULTS: Twenty-four swine were instrumented with a mid-LAD perfusion catheter for regional infusion of lidocaine 0.75 mg. kg(-1). h(-1) (n=7), low-dose d-sotalol (0.16 mg. kg(-1). h(-1)) (n=4), high-dose d-sotalol (0.5 mg. kg(-1). h(-1)) (n=6), or saline (n=7). Effective refractory periods (ERPs) were determined at 5 myocardial sites, and regional conduction velocity was determined in LAD-perfused and -nonperfused regions. Regional lidocaine infusion increased DER values by 84% (P=0.008) and slowed conduction velocity by 23% to 35% (P<0.01) but did not affect ERP. Conversely, regional low- and high-dose d-sotalol infusion did not alter DER values or conduction velocity but increased regional ERP by 14% to 17% (P<0.001). Regional lidocaine increased conduction velocity dispersion by 100% to 200% (P=0.01) but did not change ERP dispersion, whereas d-sotalol increased ERP dispersion by 140% (P<0.001) without affecting conduction velocity dispersion. Lidocaine infusion induced ventricular fibrillation (VF) in 6 of 7 animals, whereas regional d-sotalol was not proarrhythmic. Regional infusion of lidocaine and d-sotalol prolonged VF cycle length by 23% to 41% (P<0.05) in the perfused region and increased VF cycle length dispersion by 85% to 240% (P<0.05). Both agents increased pacing threshold (excitability) in the perfused region by 93% to 116% (P<0.05). CONCLUSIONS: Regional conduction velocity slowing increased DER values, which was probably a result of spatial dispersion of conduction velocity. Increasing refractory period dispersion without changing conduction velocity did not alter DFT values. Thus, dispersion of conduction velocity may be a more likely regulator of defibrillation efficacy than dispersion of refractoriness.

Impaired endothelium-mediated relaxation in coronary arteries from insulin-resistant rats.

OBJECTIVE: The insulin resistance syndrome is associated with atherosclerosis and cardiovascular events; however, the underlying mechanism of vascular dysfunction is unknown. The purpose of the current study was to assess endothelium- and smooth-muscle-mediated vasodilation in isolated coronary arteries from insulin-resistant rats and to determine whether insulin resistance alters the activity of the specific endothelium-derived relaxing factors. METHODS: Male Sprague-Dawley rats were randomized to insulin resistance or control. Insulin resistance was induced by a fructose-rich diet. After 4 weeks of diet, coronary arteries were removed and vascular function was assessed in vitro using videomicroscopy. Acetylcholine (10(-9)-3 x 10(-5) M)- or sodium-nitroprusside (10(-9)-3 x 10(-4) M)-induced relaxations were determined. To evaluate the role of the specific endothelium-derived relaxing factors, several inhibitors were used, including N-nitro-L-arginine (LNNA), charybdotoxin/apamin (CTX/apamin), and indomethacin. RESULTS: Studies with nitroprusside showed that smooth-muscle-dependent relaxation did not differ between insulin resistance and control groups. In contrast, maximal relaxation (E(max)) to acetylcholine was decreased in the insulin resistance group (56 +/- 7%) versus control (93 +/- 3%). LNNA pretreatment further impaired E(max) in the IR group from 56 +/- 7 to 17 +/- 2% (p < 0.01). In control, E(max) was only slightly impaired by LNNA (93 +/- 3 to 63 +/- 6%; p < 0.05). The addition of CTX/apamin also decreased relaxation in the control group (93 +/- 3 to 47 +/- 7%; p < 0.05), whereas relaxation in insulin-resistant rats was not affected (45 +/- 5% with CTX/apamin vs. 56 +/- 7% with acetylcholine alone, NS). Pretreatment with indomethacin did not affect relaxation in either group, while pretreatment with the combination of LNNA and CTX/ apamin completely abolished relaxation in both groups. CONCLUSIONS: Endothelium-dependent relaxation is impaired in small coronary arteries from insulin-resistant rats. The mechanism of this defect is related to a decrease in an endothelium-dependent, nitric oxide/prostanoid-independent relaxing factor or endothelium-derived hyperpolarizing factor.

EDHF-mediated relaxation is impaired in fructose-fed rats.

Insulin resistance (IR) is associated with endothelial dysfunction. A defect in endothelium-dependent relaxation via outward potassium conductance has been observed in mesenteric arteries from IR rats. The purpose of this study was to assess whether this defect in endothelium-dependent relaxation was due to impaired endothelium-derived hyperpolarizing factor (EDHF) and to determine which specific potassium channel(s) are involved in relaxation. This was accomplished by using specific potassium channel inhibitors in the presence of nitric oxide synthase and cyclooxygenase inhibition. In addition, we sought to assess the function of smooth muscle cell adenosine triphosphate (ATP)-dependent potassium (K(ATP)) channels. Sprague-Dawley rats were randomized to control or IR. To determine EDHF-mediated relaxation, acetylcholine (ACh)-induced (10(-9)-10(-5) M) relaxation was measured (in vitro) in mesenteric arteries in the presence of indomethacin (10(-5) M) and N-nitro-L-arginine (L-NNA) (10(-4) M). Subsequently the combination of charybdotoxin (CTX) (0.1 microM) and apamin (0.5 microM) or glibenclamide (Glib) (10 microM) was added to the bath to inhibit KCa or K(ATP), respectively. In separate experiments, relaxation to pinacidil (10(-13)-10(-5) M), a K(ATP) activator, was assessed in vessels with intact endothelium, endothelium denuded, or with L-NNA. Maximal relaxation to ACh in the presence of L-NNA and indomethacin was 68+/-6% for control and 12+/-3% for IR (p<0.01). The addition of CTX + apamin almost abolished EDHF-mediated relaxation in control (Emax, 8+/-5% vs. 68+/-6%; p<0.01), whereas Glib had little affect. Neither CTX + apamin nor Glib had any affect on IR. Additionally, IR arteries were less sensitive to pinacidil than were controls (EC50, 1.5+/-0.9 microM vs. 5x10(-4)+/-3x10(-4) microM, respectively; p<0.01). Endothelial removal or L-NNA pretreatment of control arteries decreased the response to pinacidil similar to IR, whereas IR vessels were unaffected. EDHF-mediated relaxation is impaired in IR arteries. In addition, the K(Ca) channel appears to be imperative for activity of EDHF in rat small mesenteric arteries. Moreover, activation of K(ATP) channels by pinacidil is impaired in IR, and this appears to be a result of endothelial dysfunction.

Action potentials that mimic fibrillation activate sodium current.

Ventricular fibrillation (VF) has brief action potentials (50-70 ms) with short diastolic intervals (10-30 ms). Under these conditions ion channel activity may be grossly different to normal sinus rhythm (NSR). In particular, sodium channel activation may not contribute to the generation and propagation of action potentials during VF. This study determined if sodium channels can be activated when action potentials mimic VF. Isolated chick ventricular myocytes (n=7) were voltage-clamped to quantitate fast inward sodium current. The voltage clamp protocol simulated VF with a 10 pulse train at 10 Hz (100 ms cycle length (CL)) and depolarization interval (action potential duration) ranging from 90 to 20 ms. After each train a test pulse was delivered from holding (-80 mV) in 10-ms steps. The train preceded each step pulse. Peak sodium current for control and each VF protocol occurred at a membrane potential (V(m)) of -10 mV. Sodium current was evident during brief resting intervals as short as 20 ms, albeit 10-20% of baseline. Resting intervals less than 60 ms shifted the sodium conductance activation curve from Vm(0.5)-30 mV to -22 mV membrane potential. Similar findings occurred when resting potential was at -65 mV, although there was less sodium current with all tested protocols. There was significantly less inactivation of sodium current when the prepulse was shorter (100 v 1000 ms). There was approximately 20% greater sodium current when the test pulse followed a short v long depolarized (>-80 mV) prepulse. Although the longer depolarization pulses produce approximately 20% greater sodium current at membrane potentials more negative than -80 mV. Lastly the time for half recovery of sodium current from activation was significantly less when the inactivating prepulse was short v long (45.9+/-9 v 118+/-20 ms, P<0.05). In conclusion, sodium current is evident when the diastolic rest interval is as brief as 10-20 ms. Rest interval, length of membrane depolarization and membrane potential interact to affect sodium channel activation, inactivation and recovery from inactivation. These data demonstrate that the brief action potentials at more depolarized membrane potentials seen during VF allow for inward sodium current upon depolarization, less sodium channel inactivation, and a faster recovery from inactivation, thereby compensating for a short diastolic rest interval. Therefore, it is likely that the inward sodium channel contributes to wave front propagation during ventricular fibrillation.

Impaired vagal reflex activity in insulin-resistant rats.

Insulin resistance, without frank diabetes, is associated with sudden cardiac death. We postulated that a potential mechanism for this association is autonomic dysfunction. Male Sprague-Dawley rats were randomized into one of two groups: (a) insulin resistant (IR; n = 15), or (b) control (n = 11). Animals were made insulin resistant with a fructose-rich diet, whereas control animals received standard rat chow. Four weeks after randomization, arterial pressure and baroreceptor reflex were assessed. Baroreflex sensitivity was defined as the heart-rate response to acute blood pressure changes caused by nitroprusside (0.5-18 micrograms) or phenylephrine (0.2-3 micrograms). To determine the role of vagal stimulation specifically, each animal was randomized to receive atropine sulfate (1 mg/kg) or vehicle (normal saline) before administration of phenylephrine. Mean arterial pressure and fasting insulin concentrations were increased in the insulin-resistant group, whereas there were no differences in body weight, fasting glucose concentrations, or resting heart rate. Phenylephrine increased arterial blood pressure to a maximum of 54 +/- 2 mm Hg for control and 45 +/- 6 mm Hg for IR, p = 0.7. The maximal heart-rate change response to the increased blood pressure was markedly blunted in IR as compared with control (-88 +/- 12 beats/min for IR vs. -238 +/- 18 beats/min for control; p < 0.001). Thus the baroreflex sensitivity (BRS) was threefold less in IR versus the control group (-1.8 +/- 0.2 vs. -4.6 +/- 0.7 beats/min/mm Hg; p = 0.001). Pretreatment with atropine sulfate decreased the BRS in both groups, eliminating the difference between groups (-0.96 +/- 0.5 beats/min/mm Hg for control and -0.56 +/- 0.3 beats/min/mm Hg for IR; p = 0.2). Thus atropine sulfate caused the phenylephrine-induced heart rate and arterial blood pressure response to be equal between groups. On the other hand, BRS to nitroprusside-induced blood pressure changes were similar between groups. Insulin resistance, without the confounding factors of obesity, diabetes, and significant hypertension, is associated with a large reduction in vagal activity, which occurs via attenuation in reflex activity. In contrast, the insulin-resistant syndrome does not affect baroreflex sensitivity via sympathetic reflex.

Endothelial dysfunction precedes hypertension in diet-induced insulin resistance.

The insulin-resistant (IR) syndrome may be an impetus for the development of hypertension (HTN). Unfortunately, the mechanism by which this could occur is unclear. Our laboratory and others have described impaired endothelium-mediated relaxation in IR, mildly hypertensive rats. The purpose of the current study is to determine if HTN is most likely a cause or result of impaired endothelial function. Sprague-Dawley rats were randomized to receive a fructose-rich diet for 3, 7, 10, 14, 18, or 28 days or were placed in a control group. The control group received rat chow. After diet treatment, animals were instrumented with arterial cannulas, and while awake and unrestrained, their blood pressure (BP) was measured. Subsequently, endothelium-mediated relaxation to acetylcholine was determined (in vitro) by measuring intraluminal diameter of phenylephrine-preconstricted mesenteric arteries ( approximately 250 microM). Serum insulin levels were significantly elevated in all groups receiving fructose feeding compared with control, whereas there were no differences in serum glucose levels between groups. Impairment of endothelium-mediated relaxation starts by day 14 [mean percent maximal relaxation (Emax): 69 +/- 10% of baseline] and becomes significant by day 18 (Emax: 52 +/- 11% of baseline; P < 0.01). However, the mean BP (mmHg) does not become significantly elevated until day 28 [BP: 132 +/- 1 (day 28) vs. 116 +/- 3 (control); P < 0.05]. These findings demonstrate that both IR and endothelial dysfunction occur before HTN in this model and suggest that endothelial dysfunction may be a mechanism linking insulin resistance and essential HTN.

Disparate effects of biphasic and monophasic shocks on postshock refractory period dispersion.

The magnitude by which a defibrillation shock extends the refractory period immediately postshock (refractory period extension, RPE) does not explain why biphasic shocks defibrillate with greater efficacy than monophasic shocks. It may be that spatial heterogeneity of RPE is a more important regulator of defibrillation efficacy. We measured RPE in 15 pentobarbital-anesthetized swine using 400-V biphasic and monophasic shocks of equal pulse duration at three discrete myocardial sites. Spatial heterogeneity of RPE was calculated as the difference between the maximum and minimum values of the three recording sites. Monophasic shocks produced greater magnitude of RPE than biphasic shocks at all sites tested (82 +/- 6 to 99 +/- 13 and 64 +/- 6 to 68 +/- 5 ms, respectively; P < 0.05). However, RPE dispersion was significantly less with biphasic shocks versus monophasic shocks (29 +/- 4 and 48 +/- 7 ms, respectively; P < 0.05). This suggests that one potential mechanism by which biphasic shocks defibrillate with greater efficacy is limiting postshock spatial heterogeneity of refractoriness. Thus these data support our hypothesis that RPE heterogeneity is a more likely predictor of defibrillation efficacy than magnitude of RPE.