Functional differences between junctional and extrajunctional adrenergic receptor activation in mammalian ventricle

Increased cardiac sympathetic activation worsens dispersion of repolarization and is proarrhythmic. The functional differences between intrinsic nerve stimulation and adrenergic receptor activation remain incompletely understood. This study was undertaken to determine the functional differences between efferent cardiac sympathetic nerve stimulation and direct adrenergic receptor activation in porcine ventricles. Female Yorkshire pigs (n = 13) underwent surgical exposure of the heart and stellate ganglia. A 56-electrode sock was placed over the ventricles to record epicardial electrograms. Animals underwent bilateral sympathetic stimulation (BSS) (n = 8) or norepinephrine (NE) administration (n = 5). Activation recovery intervals (ARIs) were measured at each electrode before and during BSS or NE. The degree of ARI shortening during BSS or NE administration was used as a measure of functional nerve or adrenergic receptor density. During BSS, ARI shortening was nonuniform across the epicardium (F value 9.62, P = 0.003), with ARI shortening greatest in the mid-basal lateral right ventricle and least in the midposterior left ventricle (LV) (mean normalized values: 0.9 ± 0.08 vs. 0.56 ± 0.08; P = 0.03). NE administration resulted in greater ARI shortening in the LV apex than basal segments [0.91 ± 0.04 vs. 0.63 ± 0.05 (averaged basal segments); P = 0.003]. Dispersion of ARIs increased in 50% and 60% of the subjects undergoing BSS and NE, respectively, but decreased in the others. There is nonuniform response to cardiac sympathetic activation of both porcine ventricles, which is not fully explained by adrenergic receptor density. Different pools of adrenergic receptors may mediate the cardiac electrophysiological effects of efferent sympathetic nerve activity and circulating catecholamines.

Development and use of a novel cardiovascular simulator: time for a paradigm shift?

Understanding cardiovascular physiology, pharmacology, and treatment of shock is heavily emphasized in current medical school and surgical training. Performance of individuals in treatment of critical illness remains poor despite regular didactic sessions. We have developed a PC computer-based simulator capable of integrating basic hemodynamic parameters to dynamically generate a realistic patient monitor. The methodology includes physiological feedback as found in humans. The trainees are able to learn through a series of scenarios or ad lib manipulation of parameters. Participants including medical students, nurses, and residents were given a pretest before attending either a 30-minute didactic or a 10- or 30-minute simulator session. A posttest was administered to evaluate performance after the intervention. Twenty-four participants were equally randomized with 12 receiving simulator training. Although the two groups had similar pretest scores (P>0.5), the simulator group showed a 24 per cent improvement, whereas the lecture group showed a 10 per cent improvement in the posttest score (P=0.008). Simulations in surgery and critical care are in early stages of development. Access to such simulators on a personal computer can greatly enhance understanding of the cardiovascular system. These simulators appear to be very effective and may become an integral adjunct to traditional classroom teaching methods.

Cardioprotection of electroacupuncture against myocardial ischemia-reperfusion injury by modulation of cardiac norepinephrine release

Augmentation of cardiac sympathetic tone during myocardial ischemia has been shown to increase myocardial O(2) demand and infarct size as well as induce arrhythmias. We have previously demonstrated that electroacupuncture (EA) inhibits the visceral sympathoexcitatory cardiovascular reflex. The purpose of this study was to determine the effects of EA on left ventricular (LV) function, O(2) demand, infarct size, arrhythmogenesis, and in vivo cardiac norepinephrine (NE) release in a myocardial ischemia-reperfusion model. Anesthetized rabbits (n = 36) underwent 30 min of left anterior descending coronary artery occlusion followed by 90 min of reperfusion. We evaluated myocardial O(2) demand, infarct size, ventricular arrhythmias, and myocardial NE release using microdialysis under the following experimental conditions: 1) untreated, 2) EA at P5-6 acupoints, 3) sham acupuncture, 4) EA with pretreatment with naloxone (a nonselective opioid receptor antagonist), 5) EA with pretreatment with chelerythrine (a nonselective PKC inhibitor), and 6) EA with pretreatment with both naloxone and chelerythrine. Compared with the untreated and sham acupuncture groups, EA resulted in decreased O(2) demand, myocardial NE concentration, and infarct size. Furthermore, the degree of ST segment elevation and severity of LV dysfunction and ventricular arrhythmias were all significantly decreased (P < 0.05). The cardioprotective effects of EA were partially blocked by pretreatment with naloxone or chelerythrine alone and completely blocked by pretreatment with both naloxone and chelerythrine. These results suggest that the cardioprotective effects of EA against myocardial ischemia-reperfusion are mediated through inhibition of the cardiac sympathetic nervous system as well as opioid and PKC-dependent pathways.

Vertebral artery dissection after iatrogenic cervical subcutaneous emphysema

We report a case of spontaneous vertebral artery dissection (VAD) in a patient who developed extensive subcutaneous emphysema following the removal of a chest tube after a cardiac transplant. The pathophysiology and management of this uncommon complication are reviewed. Although vertebral and carotid artery dissections are unusual events occurring in 2.5 to 3 per 100,000 people, they are increasingly acknowledged to be important causes of stroke in the young and middle-aged adult population accounting for up to 25% of such cases. VADs are associated with a variety of minor traumatic mechanisms including painting a ceiling, yoga, chiropractic manipulation of the spine, and driving. These events cause injury to the vessel wall either by shearing forces secondary to rotational injuries or direct trauma to the vessel wall on bony prominences, especially the transverse processes of the cervical vertebrae. We present a case of a patient with documented previously normal vertebral arterial anatomy who developed a VAD after mediastinal tube removal resulted in subcutaneous emphysema tracking through fascial planes into his neck.

Surgery of the pretransversal vertebral artery: indications and results

AIM

The aim of this study was to evaluate our results with elective vertebral arteries surgery, to emphasize the indications of such revascularization and to compare it with previous larger studies.

METHODS

The medical records of all patients who underwent a pretransversal vertebral artery (VA) revascularization between 1990 and 2004 at our University Hospital were retrospectively reviewed.

RESULTS

Forty patients, with a mean age of 60.5 years, met the criteria for VA surgery and accounted for 4.2% of the vascular surgeries involving the brain. Seventeen (42.5%) patients presented with vertebrobasilar insufficiency of hemodynamic origin, 16 (40%) with embolism, and 7 (17.5%) had no neurological symptoms. Direct vertebrocarotid reimplantation was the main procedure performed. No death or stroke occurred preoperatively or during the perioperative period. Mean follow-up was 31 months. Overall survival was 86.9% at 3 years and the primary patency rate was 97.5% at 3 years.

CONCLUSION

Our study confirms the good results achieved by the pretransversal conventional VA surgery. This surgery remains few in number despite the fact that about 25% of ischemic strokes occur in the vertebrobasilar region. Vertebrobasilar signs should be better recognized to avoid performing this type of procedure merely based on imaging criteria.

Iliac fixation inhibits migration of both suprarenal and infrarenal aortic endografts

OBJECTIVE

To evaluate the role of iliac fixation in preventing migration of suprarenal and infrarenal aortic endografts.

METHODS

Quantitative image analysis was performed in 92 patients with infrarenal aortic aneurysms (76 men and 16 women) treated with suprarenal (n = 36) or infrarenal (n = 56) aortic endografts from 2000 to 2004. The longitudinal centerline distance from the superior mesenteric artery to the top of the stent graft was measured on preoperative, postimplantation, and 1-year three-dimensional computed tomographic scans, with movement more than 5 mm considered to be significant. Aortic diameters were measured perpendicular to the centerline axis. Proximal and distal fixation lengths were defined as the lengths of stent-graft apposition to the aortic neck and the common iliac arteries, respectively.

RESULTS

There were no significant differences in age, comorbidities, or preoperative aneurysm size (suprarenal, 6.0 cm; infrarenal, 5.7 cm) between the suprarenal and infrarenal groups. However, the suprarenal group had less favorable aortic necks with a shorter length (13 vs 25 mm; P < .0001), a larger diameter (27 vs 24 mm; P < .0001), and greater angulation (19 degrees vs 11 degrees ; P = .007) compared with the infrarenal group. The proximal aortic fixation length was greater in the suprarenal than in the infrarenal group (22 vs 16 mm; P < .0001), with the top of the device closer to the superior mesenteric artery (8 vs 21 mm; P < .0001) as a result of the 15-mm uncovered suprarenal stent. There was no difference in iliac fixation length between the suprarenal and infrarenal groups (26 vs 25 mm; P = .8). Longitudinal centerline stent graft movement at 1 year was similar in the suprarenal and infrarenal groups (4.3 +/- 4.4 mm vs 4.8 +/- 4.3 mm; P = .6). Patients with longitudinal centerline movement of more than 5 mm at 1 year or clinical evidence of migration at any time during the follow-up period comprised the respective migrator groups. Suprarenal migrators had a shorter iliac fixation length (17 vs 29 mm; P = .006) and a similar aortic fixation length (23 vs 22 mm; P > .999) compared with suprarenal nonmigrators. Infrarenal migrators had a shorter iliac fixation length (18 vs 30 mm; P < .0001) and a similar aortic fixation length (14 vs 17 mm; P = .1) compared with infrarenal nonmigrators. Nonmigrators had closer device proximity to the hypogastric arteries in both the suprarenal (7 vs 17 mm; P = .009) and infrarenal (8 vs 24 mm; P < .0001) groups. No migration occurred in either group in patients with good iliac fixation. Multivariate logistic regression analysis revealed that iliac fixation, as evidenced by iliac fixation length (P = .004) and the device to hypogastric artery distance (P = .002), was a significant independent predictor of migration, whereas suprarenal or infrarenal treatment was not a significant predictor of migration. During a clinical follow-up period of 45 +/- 22 months (range, 12-70 months), there have been no aneurysm ruptures, abdominal aortic aneurysm-related deaths, or surgical conversions in either group.

CONCLUSIONS

Distal iliac fixation is important in preventing migration of both suprarenal and infrarenal aortic endografts that have longitudinal columnar support. Secure iliac fixation minimizes the risk of migration despite suboptimal proximal aortic neck anatomy. Extension of both iliac limbs to cover the entire common iliac artery to the iliac bifurcation seems to prevent endograft migration.

P19 Progenitor Cells Progress to Organized Contracting Myocytes After Chemical and Electrical Stimulation:Implications for Vascular Tissue Engineering

PURPOSE

To test the hypothesis that a level of chemical and electrical stimulation exists that allows differentiation of progenitor cells into organized contracting myocytes.

METHODS

A custom-made bioreactor with the capability of delivering electrical pulses of varying field strengths, widths, and frequencies was constructed. Individual chambers of the bioreactor allowed continuous electrical stimulation of cultured cells under microscopic observation. On day 0, 1% dimethylsulfoxide (DMSO), known to differentiate cells into myocytes, was added to P19 progenitor cells. Additionally, for the next 22 days, electrical pulses of varying field strengths (0-3 V/cm), widths (2-40 ms), and frequencies (10-25 Hz) were continuously applied. On day 5, the medium containing DMSO was exchanged with regular medium, and the electrical stimulation was continued. From days 6-22, the cells were visually assessed for signs of viability, contractility, and organization.

RESULTS

P19 cells remained viable with pulsed electrical fields <3 V/cm, pulse widths <40 ms, and pulse frequencies from 10 to 25 Hz. On day 12, the first spontaneous contractions were observed. For individual colonies, local synchronization and organization occurred; multiple colonies were synchronized with externally applied electrical fields.

CONCLUSION

P19 progenitor cells progress to organized contracting myocytes after chemical and electrical stimulation. Incorporation of such cells into existing methods of producing endothelial cells, fibroblasts, and scaffolds may allow production of improved tissue-engineered vascular grafts.

Hypericin and Pulsed Laser Therapy of Squamous Cell Cancer in Vitro

OBJECTIVE

This in vitro study compares continuous wave and pulsed laser light at longer wavelengths for activation of the phototoxic drug hypericin in human cancer cells.

BACKGROUND DATA

Two-photon pulsed laser light now allows high-resolution fluorescent imaging of cancer cells and should provide deeper tissue penetration with near infrared light for improved detection as well as phototoxicity in human tumors.

METHODS

Cultured Seoul National University (SNU)-1 tumor cells from a squamous cell carcinoma (SCC) were incubated with hypericin before photoirradiation at four laser wavelengths. Phototoxicity of hypericin sensitized SCC cells was measured by dimethyl thiazoldiphenyl (MTT) tetrazolium bromide cell viability assays and by confocal fluorescence microscopy via 532-nm and infrared two-photon pulsed laser light.

RESULTS

Phototoxic response increased linearly with hypericin dose of 0.1-2 microM, light exposure time of 5-120 sec, and pulsed dye laser wavelengths of 514-593 nm. Light energy delivery for 50% cell phototoxicity (LD50) response was 9 joules at 514 nm, 3 joules at 550 nm, and less than 1 joule at the 593 nm hypericin light absorption maxima. Fluorescence confocal microscopy revealed membrane and perinuclear localization of hypericin in the SNU cells with membrane damage seen after excitation with visible 532 nm continuous wave light or two-photon 700-950 nm picosecond pulsed laser irradiation.

CONCLUSIONS

Hypericin may be a powerful tumor targetting drug when combined with pulsed laser light in patients with recurrent head and neck SCC.

A Novel Culture System Shows that Stem Cells Can be Grown in 3D and Under Physiologic Pulsatile Conditions for Tissue Engineering of Vascular Grafts

BACKGROUND

Currently available vascular grafts have been limited by variable patency rates, material availability, and immunological rejection. The creation of a tissue-engineered vascular graft (TEVG) from autologous stem cells would potentially overcome these limitations. As a first step in creating a completely autologous TEVG, our objective was to develop a novel system for culturing undifferentiated mouse embryonic stem cells (mESC) in a three-dimensional (3D) configuration and under physiological pulsatile flow and pressure conditions.

MATERIALS AND METHODS

A bioreactor was created to provide pulsatile conditions to a specially modified four-well Labtek Chamber-Slide culture system. Undifferentiated mESC were either suspended in a 3D Matrigel matrix or suspended only in cell-culture media within the culture system. Pulsatile conditions were applied to the suspended cells and visualized by video microscopy.

RESULTS

Undifferentiated mESC were successfully embedded in a 3D Matrigel matrix and could withstand physiological pulsatile conditions. Video microscopy demonstrated that the mESC in the 3D matrix were constrained to the wells of the culture system, moved in unison with the applied flows, and were not washed downstream; this was in contrast to the mESC suspended in media alone.

CONCLUSIONS

Undifferentiated mESC can be grown in 3D and under pulsatile conditions. We will use these results to study the effects of long-term pulsatile conditions on the differentiation of mESC into endothelial cells, smooth muscle cells, and fibroblast cells with the long-term goal of creating a completely autologous TEVG.

Use of recombinant factor VIIa for adjunctive hemorrhage control in trauma and surgical patients

Recombinant factor VIIa (rFVIIa) has recently been described for patients with ongoing massive bleeding in a number of different clinical scenarios. A retrospective chart review was conducted at a public level I trauma center in order to describe the use of rFVIIa in trauma and surgical patients with massive bleeding despite surgical control. Fifteen trauma and general surgical patients underwent major operative procedures and developed coagulopathy requiring massive blood product transfusion. All patients had continued life-threatening hemorrhage despite surgical control of bleeding. The mean base deficit was 6 and arterial lactate was 9.0 mmol/L. An initial dose of rFVIIa was given intravenously, followed by a second dose if there was evidence of at least a partial response. Twelve of 15 patients who had been expected to die from hemorrhage survived for greater than 48 hours, and 7 survived to hospital discharge. A partial or complete hemostatic response to rFVIIa was noted in 12 of 15 patients. The number of blood products received after administration of rFVIIa was significantly reduced and the International Normalized Ratio (INR) decreased. Our experience demonstrates that rFVIIa may reduce or completely arrest coagulopathic bleeding in trauma and surgical patients after vascular control.

Administration of nesiritide in patients after coronary artery bypass surgery induces brisk diuresis

Recombinant human brain natriuretic peptide, nesiritide, has recently been used in limited studies to enhance postoperative diuresis. A retrospective chart review was conducted at a university hospital to assess the efficacy of nesiritide in cardiac surgery patients with fluid overload refractory to diuretics and dopamine. Nine out of 137 patients who underwent coronary artery bypass grafting at the institution from May 2003 to July 2004 exhibited fluid overload despite diuretics and dopamine. Those who did not respond to the therapy, as manifested by oliguria and heart failure, were started on nesiritide. Urine output, weight change, central venous pressure (CVP), pulmonary artery wedge pressure (PAWP), and serum creatinine were the main outcome measures. Within 6 hours after initiation of nesiritide, the average urine output increased from 28 to 130 mL/h. Serum creatinine levels were not significantly different after 24 hours. The mean CVP decreased from 14 to 10 within 12 hours while the PAWP decreased from 24 to 17 mm Hg. Systemic pressures did not change. One patient had to eventually undergo hemodialysis for complications of renal failure. Our experience demonstrates that infusion of nesiritide in patients with heart failure and fluid overload improves diuresis and hemodynamics without major side effects.

Administration of Nesiritide in Patients after Coronary Artery Bypass Surgery Induces Brisk Diuresis

Recombinant human brain natriuretic peptide, nesiritide, has recently been used in limited studies to enhance postoperative diuresis. A retrospective chart review was conducted at a university hospital to assess the efficacy of nesiritide in cardiac surgery patients with fluid overload refractory to diuretics and dopamine. Nine out of 137 patients who underwent coronary artery bypass grafting at the institution from May 2003 to July 2004 exhibited fluid overload despite diuretics and dopamine. Those who did not respond to the therapy, as manifested by oliguria and heart failure, were started on nesiritide. Urine output, weight change, central venous pressure (CVP), pulmonary artery wedge pressure (PAWP), and serum creatinine were the main outcome measures. Within 6 hours after initiation of nesiritide, the average urine output increased from 28 to 130 mL/h. Serum creatinine levels were not significantly different after 24 hours. The mean CVP decreased from 14 to 10 within 12 hours while the PAWP decreased from 24 to 17 mm Hg. Systemic pressures did not change. One patient had to eventually undergo hemodialysis for complications of renal failure. Our experience demonstrates that infusion of nesiritide in patients with heart failure and fluid overload improves diuresis and hemodynamics without major side effects.