Shuji Shimizu

In vivo direct monitoring of vagal acetylcholine release to the sinoatrial node

To directly monitor vagal acetylcholine (ACh) release into the sinoatrial node, which regulates heart rate, we implanted a microdialysis probe in the right atrium near the sinoatrial node and in the right ventricle of anesthetized rabbits, and perfused with Ringers solution containing eserine. (1) Electrical stimulation of right or left cervical vagal nerve decreased atrial rate and increased dialysate ACh concentration in the right atrium in a frequency-dependent manner. Compared to left vagal stimulation, right vagal nerve stimulation decreased atrial rate to a greater extent at all frequencies, and increased dialysate ACh concentration to a greater extent at 10 and 20 Hz. However, dialysate ACh concentration in the right atrium correlated well with atrial rate independent of whether electrical stimulation was applied to the right or left vagal nerve (atrial rate=304-131 x log[ACh], R(2)=0.77). (2) Right or left vagal nerve stimulation at 20 Hz decreased atrial rate and increased dialysate ACh concentrations in both the right atrium (right, 17.9+/-4.0 nM; left, 7.9+/-1.4 nM) and right ventricle (right, 0.9+/-0.3 nM; left, 1.0+/-0.4 nM). However, atrial dialysate ACh concentrations were significantly higher than ventricular concentrations, while ventricular dialysate ACh concentrations were not significantly different between right and left vagal nerve stimulation. (3) The response of ACh release to right and left vagal nerve stimulation was abolished by intravenous administration of a ganglionic blocker, hexamethonium bromide. In conclusion, ACh concentration in dialysate from the right atrium, sampled by microdialysis, is a good marker of ACh release from postganglionic vagal nerves to the sinoatrial node.

In vivo direct monitoring of interstitial norepinephrine levels at the sinoatrial node.

We assessed in vivo interstitial norepinephrine (NE) levels at the sinoatrial node in rabbits, using microdialysis technique. A dialysis probe was implanted adjacent to the sinoatrial node of an anesthetized rabbit and dialysate was sampled during sympathetic nerve stimulation. Atrial dialysate NE concentration correlated well with heart rate. Desipramine significantly increased dialysate NE concentrations both before and during sympathetic nerve stimulation compared with the absence of desipramine. However, desipramine did not affect the relation between heart rate and dialysate NE concentration. These results suggest that atrial dialysate NE level reflects the relative change of NE concentration in the synaptic cleft. Microdialysis is a powerful tool to assess in vivo interstitial NE levels at the sinoatrial node.

Norwood procedure with non-valved right ventricle to pulmonary artery shunt improves ventricular energetics despite the presence of diastolic regurgitation: a theoretical analysis

When the Norwood procedure is conducted for the hypoplastic left heart syndrome using a non-valved right ventricle (RV) to pulmonary artery (PA) shunt, diastolic regurgitation from PA to RV may have an adverse effect on postoperative hemodynamics. In this study, we examined the impact of the diastolic regurgitation on ventricular energetics by computational analysis using a combination of a time-varying elastance chamber model and a modified three-element Windkessel vascular model. This study revealed that use of the valved or non-valved RV-PA shunt eliminated pulmonary over-circulation which was observed when using the systemic to pulmonary artery shunt (modified Blalock–Taussig shunt). Although the valved RV-PA shunt improved pulmonary blood supply and consequently increased pulmonary artery flow and oxygen saturation compared to the non-valved RV-PA shunt, the non-valved RV-PA shunt improved ventricular energetics in spite of the presence of PA to RV regurgitation.

Successful one-stage surgical removal of intravenous leiomyomatosis with cardiac extension in an elderly patient

Intravenous leiomyomatosis is a benign smooth muscle tumor that sometimes spreads to the right heart via the inferior vena cava. A complete surgical resection is necessary to ensure its successful treatment. Surgical removal has been performed safely in middle-aged patients. Here we report a case of successful surgical removal in an elderly woman (age 81 years). The woman was admitted with palpitation and diagnosed as having an intravenous leiomyomatosis with cardiac extension. She underwent a one-stage surgical removal with cardiopulmonary bypass and circulatory arrest. We therefore recommend a one-stage operation, if possible, even in elderly patients.

Hybrid stage I palliation for hypoplastic left heart syndrome has no advantage on ventricular energetics: a theoretical analysis

A hybrid procedure combining bilateral pulmonary artery banding with ductal stenting has recently been used as stage I palliation for hypoplastic left heart syndrome. However, the advantage of the hybrid procedure over the Norwood procedure on ventricular energetics remains unclear. To clarify this, we performed a computational analysis with a combination of time-varying elastance chamber model and modified three-element Windkessel vascular model. Although mean pulmonary artery (PA) pressure, pulmonary flow, and oxygen saturation were almost equivalent with the Norwood procedure, the hybrid procedure delivered higher systolic and lower diastolic systemic arterial pressures compared to the Norwood procedure with right ventricle (RV) to PA shunt. As a result, the hybrid procedure yielded increased systolic pressure–volume area and impaired mechanical efficiency. Therefore, the hybrid procedure has probably no advantage on ventricular energetics compared to the Norwood procedure with a RV-PA shunt.

Effects of intravenous cariporide on release of norepinephrine and myoglobin during myocardial ischemia/reperfusion in rabbits

AIMS To examine the effects of cariporide, a Na(+)/H(+) exchanger-1 inhibitor, on cardiac norepinephrine (NE) and myoglobin release during myocardial ischemia/reperfusion by applying a microdialysis technique to the rabbit heart. MAIN METHODS In anesthetized rabbits, two dialysis probes were implanted into the left ventricular myocardium and were perfused with Ringers solution. Cariporide (0.3mg/kg) was injected intravenously, followed by occlusion of the left circumflex coronary artery. During 30-min coronary occlusion followed by 30-min reperfusion, four consecutive 15-min dialysate samples (two during ischemia and two during reperfusion) were collected in vehicle and cariporide-treated groups. Dialysate myoglobin and NE concentrations were measured by immunochemistry and high-performance liquid chromatography, respectively. KEY FINDINGS Dialysate myoglobin and NE concentrations increased significantly during myocardial ischemia/reperfusion in both vehicle and cariporide-treated groups (P<0.01 vs. baseline). In cariporide-treated group, dialysate myoglobin concentrations were significantly lower than those in vehicle group throughout ischemia/reperfusion (P<0.01 at 0-15 min of ischemia, P<0.05 at 15-30 min of ischemia, P<0.01 at 0-15 min of reperfusion, and P<0.01 at 15-30 min of reperfusion). However, dialysate NE concentrations in cariporide-treated group were lower than those in vehicle group only during ischemia (P<0.01 at 0-15 min of ischemia, and P<0.05 at 15-30 min of ischemia). SIGNIFICANCE When administered before ischemia, cariporide reduces myoglobin release during ischemia/reperfusion and decreases NE release during ischemia.

Apico-Brachiocephalic Artery Bypass for Aortic Stenosis With Porcelain Aorta

Apicoaortic bypass for left ventricular outflow tract obstruction has been performed with acceptable mid-term mortality. However, sometimes it is difficult to anastomose the distal end of the conduit to the calcified descending aorta in patients with a porcelain aorta. We report an aortic non-touch modification of the apicoaortic bypass in an 80-year-old woman with valvular aortic stenosis and a porcelain aorta extending from the ascending to abdominal aorta. We performed apico-brachiocephalic artery bypass under circulatory arrest with deep hypothermia. This procedure may become a useful surgical option for patients with a severe porcelain aorta.

High-cut characteristics of the baroreflex neural arc in rats

The arterial baroreflex system may be divided into the neural arc (from pressure input to efferent sympathetic nerve activity) and the peripheral arc (from sympathetic nerve activity to arterial pressure). In rabbits, the baroreflex neural arc reveals derivative characteristics in the frequency range below 0.8 Hz and high-cut characteristics above 0.8 Hz. To examine such high-cut characteristics are also present in rats, we isolated the carotid sinus regions in anesthetized rats (n = 5) and imposed a Gaussian white noise input with a switching interval of 50 ms. The transfer function of the baroreflex neural arc showed derivative characteristics in the frequency range from 0.1 to 1.3 Hz and high-cut characteristics above 1.3 Hz in rats. These results indicate that the baroreflex neural arc possesses high-cut characteristics in rats as well as in rabbits, which may contribute to preserving baroreflex gain against pulsatile pressure.