Chronic augmentation of the parasympathetic tone to the atrioventricular node: a nonthoracotomy neurostimulation technique for ventricular rate control during atrial fibrillation

INTRODUCTION

The right inferior ganglionated plexus (RIGP) selectively innervates the atrioventricular node. Temporary electrical stimulation of this plexus reduces the ventricular rate during atrial fibrillation (AF). We sought to assess the feasibility of chronic parasympathetic stimulation for ventricular rate control during AF with a nonthoracotomy intracardiac neurostimulation approach.

METHODS AND RESULTS

In 9 mongrel dogs, the small endocardial area inside the right atrium, which overlies the RIGP, was identified by 20 Hz stimulation over a guiding catheter with integrated electrodes. Once identified, an active-fixation lead was implanted. The lead was connected to a subcutaneous neurostimulator. An additional dual-chamber pacemaker was implanted for AF induction by rapid atrial pacing and ventricular rate monitoring. Continuous neurostimulation was delivered for 1-2 years to decrease the ventricular rate during AF to a range of 100-140 bpm. Implantation of a neurostimulation lead was achieved within 37 +/- 12 min. The latency of the negative dromotropic response after on/offset or modulation of neurostimulation was <1 s. Continuous neurostimulation was effective and well tolerated during a 1-2 year follow-up with a stimulation voltage <5 V. The neurostimulation effect displayed a chronaxie-rheobase behavior (chronaxie time of 0.07 +/- 0.02 ms for a 50% decrease of the ventricular rate during AF).

CONCLUSION

Chronic parasympathetic stimulation can be achieved via a cardiac neurostimulator. The approach is safe, effective, and well tolerated in the long term. The atrioventricular nodal selectivity and the opportunity to adjust the negative dromotropic effect within seconds may represent an advantage over pharmacological rate control.

Initial experience with remote magnetic navigation for left ventricular lead placement

BACKGROUND

A novel magnetic navigation system allows remote steering of guidewires and catheters. This system may be used for left ventricular lead placement for cardiac resynchronization therapy (CRT). We sought to evaluate the feasibility and safety of magnetic guidewire navigation for CRT procedures.

METHODS

123 consecutive patients underwent CRT implantation/revision procedures (including pacemaker upgrades in n=22 and left ventricular lead placement after dislocation in n=4 patients). Left ventricular lead placement in a coronary sinus side branch was performed either conventionally or using magnetic navigation. The magnetic navigation system (Niobe) consists of two permanent magnets creating a steerable magnetic field. Guidewires with integrated magnets align to the magnetic field and were used for over-the-wire implantation of pacemaker leads in the coronary sinus. Patients were assigned to conventional (n=93) or magnetic (n=30) navigation according to room availability. Venography of the coronary venous system was performed to select a target vessel for lead implantation.

RESULTS

Guidewire access to the target vessel was achieved in 100% using magnetic navigation compared to 87% with the conventional approach (P < 0.05). Implantation success rates, total procedure and fluoroscopy times did not differ significantly between groups. No periprocedural death and no intraoperative device dysfunction occurred in either group.The magnetic guidewire ruptured in one patient.

CONCLUSION

Left ventricular lead placement using magnetic guidewire navigation to engage the desired coronary sinus side branch can be successfully performed for CRT.

An experimental approach to reversible 'endovascular aortic valve placement'

BACKGROUND AND AIM OF THE STUDY

Beating heart aortic valve (re)placement without thoracotomy would be a desirable therapeutic strategy. In the present study, the feasibility of an endovascular aortic valve (re)placement was evaluated in an animal model.

METHODS

A self-expandable stent-valve and two different non-obstructive delivery devices were designed. Initially, the stent-valve was temporarily placed via surgically dissected carotid and subclavian arteries. After retrieval of the stent-valve, an endovascular resection of the native aortic valve was performed, followed by definitive stent-valve implantation. All procedures were performed under echocardiographic guidance.

RESULTS

Non-aortic vascular access was obtained in all animals. Via the carotid artery, the stent-valve was first placed into, and then retrieved from, the subcoronary position. Next, the native aortic valve was resected endovascularly, resulting in at least partial resection in all cases. The final step, definitive stent-valve implantation, was successful in all animals. The biological heart valve became functional after only a partial release of the stent. All animals remained hemodynamically stable after definitive implantation. Correct subcoronary position of the stent-valve was confirmed in a post-mortem examination. There was marked thrombus formation.

CONCLUSION

The study results proved the feasibility of: (i) reversible stent-valve placement with a nonobstructive technique in the beating heart; and (ii) partial endovascular resection of the aortic valve, with both procedures achieved via non-aortic access.

Late bilateral diaphragmatic rupture: Challenging diagnostic and surgical repair

A 67-year-old man was referred to our department, after a vehicle accident, with multiple bone fractures and a left blunt diaphragmatic rupture. An emergency laparatomy was performed, and the left diaphragmatic defect directly sutured. Postoperatively, a delayed right diaphragmatic rupture occurred due to progressive inflammation and muscle devitalisation. The diagnosis was challenging because the right rupture became clinically evident later after extubation. Diaphragmatic reconstruction was performed through a right thoracotomy. A high index of suspicion should always be observed for missed or delayed bilateral diaphragmatic ruptures.

A solitary chest wall metastasis from unknown primary hepatocellular carcinoma

We report a 61-year-old male smoker who was admitted to our hospital for treatment of a moderately growing tumour on the right anterolateral chest wall causing chest pain during coughing. Chest computed tomography and magnetic resonance imaging showed a 55 x 50 mm inhomogeneous mass around the 4th rib but not penetrating the subcutis and lung. Neither a preoperative technetium scintigraphy nor a needle biopsy revealed the primary nature of the tumour. The patient was treated with en bloc resection and partial resection of the adjacent 3rd and 4th rib. The frozen section diagnosis confirmed a metastasis from a primary hepatocellular carcinoma.

Induction of endotoxin tolerance improves lung function after warm ischemia in dogs

In shock models, induction of endotoxin tolerance (ET) is known to have a protective effect. The present study was designed to explore if ET is effective in protecting lungs from reperfusion injury. Twelve foxhounds were used as experimental animals. After a left thoracotomy, the left hilum was clamped for 3 h, followed by 8 h of reperfusion. In the treatment group (ET, n = 6), dogs were pretreated with incremental daily endotoxin doses of up to 60 microg/kg on day 6. The ischemia and reperfusion experiment was carried out on day 9. Control group animals (n = 6) were not subjected to endotoxin. After 8 h of observation, functional parameters of the reperfused lung of the ET and the control group were statistically different (P < 0.05) with respect to Po(2) [ET vs. control: 172.7 +/- 12.9 vs. 66.1 +/- 7.2 (SE) mmHg], compliance (16.0 +/- 1.2 vs. 8.3 +/- 1.0 ml/0.1 kPa), and the wet-to-dry ratio (9.4 +/- 0.8 vs. 16.7 +/- 1.2). After 3 h of warm ischemia and 8 h of reperfusion, pulmonary function and lung water content improved in the endotoxin-tolerant group.

Tumor necrosis factor-alpha production in whole blood after cardiopulmonary bypass: downregulation caused by circulating cytokine-inhibitory activities

OBJECTIVES

Cardiopulmonary bypass is associated with the release of proinflammatory cytokines (tumor necrosis factor alpha, interleukin 1beta, interleukin 6, and interleukin 8) and anti-inflammatory cytokines (interleukin 10 and transforming growth factor beta(1)). On the one hand this cytokine release is related to the postoperative systemic inflammatory response syndrome, and on the other hand it is related to deterioration of the immune system, for example in monocyte or polymorphonuclear neutrophil function, leading to an increased susceptibility to infections. To gain further insight into the alterations of immune cell reactivity and possible regulatory mechanisms, we studied lipopolysaccharide-induced tumor necrosis factor alpha synthesis in whole blood from cardiac surgical patients.

METHODS

Fifteen patients undergoing elective heart surgery with cardiopulmonary bypass were included in the study. Ex vivo lipopolysaccharide-induced tumor necrosis factor alpha synthesis was measured in a whole blood assay before, during, and after bypass. Corresponding tumor necrosis factor alpha messenger RNA levels were determined by semiquantitative reverse transcriptase-polymerase chain reaction. In addition, the influence of patient serum on whole blood responsiveness and its relationship to anti-inflammatory cytokines were evaluated in vitro.

RESULTS

Tumor necrosis factor alpha synthesis was significantly reduced after 30 minutes of cardiopulmonary bypass and showed the lowest values at the end of bypass (mean +/- SD 0.109 +/- 0.105 ng/10(6) white blood cells after 30 minutes of bypass and 0.050 +/- 0.065 ng/10(6) white blood cells at the end of bypass, vs 0.450 +/- 0.159 ng/10(6) white blood cells preoperatively, P <.001). As a further indication of reduced cytokine biosynthesis, diminished messenger RNA levels for tumor necrosis factor alpha were detected. Serum withdrawn from patients at the end of cardiopulmonary bypass reduced tumor necrosis factor alpha synthesis in heterologous blood from healthy volunteers highly significantly to 39.93% +/- 23.18% relative to control serum (P =.005) and preoperatively drawn serum (P =.024). This effect was dose dependent and was not specific for lipopolysaccharide-induced tumor necrosis factor alpha synthesis. Anesthesia and heparin administration did not influence tumor necrosis factor alpha production significantly. Ex vivo tumor necrosis factor alpha synthesis was negatively related to interleukin 10 serum levels, positively but weakly related to interleukin 4, and was not related to transforming growth factor beta(1) (Spearman correlation coefficients -0.565, P <.001, 0.362, P <.001, and -0.062, P =.460, respectively). However, interleukin 10 levels in patient serum after cardiopulmonary bypass were 300-fold below the quantities needed for half-maximal inhibition of tumor necrosis factor alpha synthesis in vitro. Moreover, the inhibitory activity could not be removed by immune absorption of interleukin 10.

CONCLUSIONS

These results suggest that during cardiac operations cytokine-inhibitory serum activities are released or newly formed. These activities could not be explained by the actions of interleukins 4 and 10 or transforming growth factor beta(1). Although their exact nature remains undetermined, these substances may contribute to the diminished immune cell functions after cardiopulmonary bypass and thus need further characterization.

The systemic inflammatory response syndrome following cardiac surgery: different expression of proinflammatory cytokines and procalcitonin in patients with and without multiorgan dysfunctions

Cardiopulmonary bypass is associated with an injury that may cause pathophysiological changes in the form of systemic inflammatory response syndrome (SIRS) or multiple organ dysfunction syndrome (MODS). In the present study, we investigated the inflammatory response of patients with multiple organ dysfunctions following open-heart surgery. Plasma levels of cytokines (IL-1beta, IL-6, IL-8, IL-18) and procalcitonin (PCT) were measured on the first four postoperative days in 12 adult male patients with SIRS and two or more organ dysfunctions after myocardial revascularization (MODS group), and 15 patients without organ dysfunctions (SIRS group). All cytokines (except IL-1beta) and PCT were significantly elevated in MODS patients, with peak values at the first two postoperative days. The results of our study show a different expression of members of the IL-1 family following extracorporeal circulation. For the first time, we can document that IL-18 is involved in the inflammatory response and the initiation of the MODS following cardiopulmonary bypass. In addition to APACHE-II score, PCT, IL-8, and IL-18 may be used as parameters for the prognosis of patients with organ dysfunctions after cardiac surgery. Furthermore, it must be noted that the duration of the surgical procedure is one of the most important factors for the initiation of the inflammatory response.

Pulmonary blood flow is inhomogeneously reduced after Euro Collins-preservation and lung transplantation

BACKGROUND

Vasoconstriction after lung transplantation is a well-known phenomenon, but only limited information is available on blood flow distribution after ischemia and reperfusion. The aim of our study was to determine the regional flow characteristics in transplanted and native dog lungs after 24 hours of cold storage and preservation with Euro Collins-solution.

METHODS

Six pairs of weight-matched Foxhounds (25 to 30 kg) were used. In donors and recipients, aortic and pulmonary artery catheters were inserted percutaneously and a reference withdrawal catheter was placed into the main pulmonary artery. For preservation, the lungs were perfused with modified Euro Collins-solution and stored at 4 degrees C. After 24 hours, the left lung was transplanted. Regional pulmonary blood flow was assessed by injection of colored microspheres into the right atrium using the reference withdrawal technique. Measurements of regional pulmonary blood flow were conducted twice in donors and recipients (baseline and 3 hours after reperfusion). Tissue samples from five distinct regions (apical, medial, dorsal, ventral, and lateral) were taken to assess regional pulmonary blood flow and wet-dry ratios.

RESULTS

The relative (per thousand Confidence Intervals/100 mg dry weight) regional pulmonary blood flow was significantly reduced in the transplanted lung but not in the native organ. This reduction was most pronounced in apical regions and smallest in regions close to the hilum. Edema formation occurred in both lungs, as judged from wet-to-dry ratios of lung tissue specimen.

CONCLUSIONS

Two separate processes can be observed after single lung transplantation: (1) reduced regional pulmonary blood flow, which is a regional phenomenon restricted to the transplanted organ, and (2) extensive edema affecting both the transplanted and the native lung.

Lipopolysaccharide-binding protein (LBP) and markers of acute-phase response in patients with multiple organ dysfunction syndrome (MODS) following open heart surgery

Cardiopulmonary bypass (CPB) is associated with an immunological injury that may cause pathophysiological alterations in the form of a systemic inflammatory response syndrome (SIRS) or a multiple organ dysfunction syndrome (MODS). Previous studies on this issue have reported different changes of immunological parameters during and after CPB, but there are no reports about the lipopolysaccharide-binding protein (LBP) in relationship to other markers of inflammation in patients with MODS following cardiovascular surgery. In the present study, we investigated the acute-phase response of patients with MODS of infectious and non-infectious origin following open-heart-surgery. Plasma levels of procalcitonin (PCT), c-reactive protein (CRP), interleukin-6 (IL-6), and LBP were measured in the first four postoperative days in 12 adult male patients with the signs of SIRS and two or more organ dysfunctions after myocardial revascularization (MODS-group), and 12 patients without organ insufficiencies (SIRS-group). There were no significant differences regarding age, weight, height, preoperative NYHA-classification, preoperative LVEDP, or the number of anastomosis. Patients with MODS had a significantly longer operation time, duration of ischemia, and duration of extracorporeal circulation. None of the patients in the SIRS group died, whereas in the MODS group, 4 patients died due to septic multiorgan failure. Plasma PCT and IL-6 concentrations were significantly elevated in all MODS patients. CRP and LBP showed no differences between the MODS and the SIRS group. Comparing the MODS patients with and without positive microbial findings, we found significantly elevated levels of PCT and LBP in those patients with documented infections. Our results indicate that LBP may be a new marker for the differentiation between a severe non-infectious SIRS and an ongoing bacterial sepsis in the early postoperative course following CPB, while a microbiological result is still missing.

Ischemic pre-conditioning of 5 minutes but not of 10 minutes improves lung function after warm ischemia in a canine model

BACKGROUND

Protection from reperfusion injury by ischemic pre-conditioning (IPC) before prolonged ischemia has been proven for the heart and the liver. We now assess the efficacy of IPC to protect lungs from reperfusion injury.

METHODS

Eighteen foxhounds (25 to 30 kg) were anesthetized, intubated, and ventilated with a fraction of inspired oxygen of 0.3 at a volume-controlled mode to maintain arterial pCO2 of 30 to 40 mm Hg. After left thoracotomy, we performed warm ischemia for 3 hours by clamping the left hilus, and followed with 8 hours of reperfusion (control, n = 6). In the treated groups, IPC was performed either for 5 minutes followed by 15-minute reperfusion (n = 6, IPC-5), or by 2 successive cycles of 10-minute ischemia, followed by 10-minute reperfusion (n = 6, IPC-10) before prior to the 3-hours warm-ischemia period. Pulmonary compliance and gas exchange were determined separately for each lung, and we recorded pulmonary and systemic hemodynamics. We performed bronchoalveolar lavage (BAL) at the end of the experiment and determined total protein concentration as well as tumor necrosis factor alpha (TNF-alpha) mRNA expression in cell-free supernatant and in BAL cells, respectively. We also assessed the wet/dry ratio of the lung.

RESULTS

In the controls, on reperfusion, we encountered a progressive deterioration of gas exchange, especially of the reperfused left lung, which we could largely avoid using the IPC-5 protocol. Similarly, pulmonary compliance steadily declined but was much better in the ICP-5 group. Parallel to the improvement of gas exchange and lung mechanics, we found less total alveolar protein content and TNF-alpha mRNA expression in BAL cells in the IPC-5 than in the controls. However, we did not find IPC-10 to be paralleled by a significant improvement of lung function. Neither IPC-5 nor IPC-10 influenced the pulmonary vascular resistance index or the fluid accumulation in the lung.

CONCLUSION

The major finding of the present study was that 5 minutes of IPC improved lung function after 3 hours of warm ischemia of the lung.