Venous sinus system

Blood flowing from the intestines to the liver through the hepatic portal vein often contains bacteria. Filtration of this blood is a protective function provided by the liver. Large phagocytic macrophages, referred to as Kupffer cells, line the hepatic venous sinuses. As the blood flows through these sinuses, bacteria are rapidly taken up and digested by the Kupffer cells. This system is very efficient and removes more than 99% of the bacteria from the hepatic portal blood. 

The venous anatomy is very variable. Venous blood flows centrally via the deep cerebral veins and peripherally via the superficial cerebral veins into the dural venous sinuses, which lie between the outer and meningeal inner layer of the dura and drain into the internal jugular veins (Stam 2005) (Fig. 4.4). The cerebral veins do not have valves and are thin walled, and the blood flow is often in the same direction as in neighboring arteries. There are numerous venous connections between the cerebral veins and the dural sinuses, the venous system of the meninges, skull, scalp, and nasal sinuses, allowing infection or thrombus to propagate between these vessels. 

Three patients developed bUateral venous sinus thromboses after receiving asparaginase the diagnosis and follow-up of this complication have been succinctly reviewed (9). In another patient receiving asparaginase, central nervous system thrombosis was associated with a transient acquired type II pattern of von WiUebrand s disease (10). 

The venous sinuses are spaces within dural layers that convey venous blood from veins within the cranium to the systemic venous circulation (Fig. 103-4). Venous sinuses are devoid of the elastic and muscle tissue found in all other veins and therefore have no elasticity and muscular contraction to enhance drainage. Circulation is dependent on motion. During the inhalation phase, the sinuses change from "V"-shaped to ovoid, with a resultant Increase In capacity. During this phase, the tributary veins increase drainage into the sinuses. 

Drug molecules that have traversed the physieal and enzymatic barriers of the colonic mucosa may enter the blood-eapillary bed or the lymphatic sinuses. Intact drug that reaches the venous capillaries from the submucosa is transported to the liver via the hepatic-portal system where they may undergo significant metabolism. On the other hand, uptake into the lymphatie sinuses of the colon results in direct delivery into the systemic circulation that causes less metabolic breakdown of the absorbed drug [3]. 

Transcoronary venous injection is performed with a catheter system threaded percutaneously into the coronary sinus. Initial studies in swine have confirmed the feasibility and safety of this approach [121]. This delivery method has also been used to deliver skeletal myoblasts to scarred myocardium in cardiomyopathy patients [120]. With intravascular ultrasound guidance, this approach allows the operator to extend a catheter and needle away from the pericardial space and coronary artery into the adjacent myocardium. To date, human feasibility studies have had a good safety profile. This technique is limited, however, by coronary venous tortuosity, lack of site specific targeting, and its own technically challenging nature. Unlike the transendocardial approach, in which cells are... 

The posterior cerebral artery supplies the occipital lobe and portions of the medial and inferior temporal lobe. The arterial supply of the spinal cord is derived from the vertebral arteries and the radicular arteries. The brain is supplied by the internal carotid arteries (the anterior circulation) and the vertebral arteries, which join at the pon tomedullary junction to form the basilar artery (collectively termed the posterior circulation). The brainstem is supplied by the posterior system. The medulla receives blood from branches of the vertebral arteries as well as from the spinal arteries and the posterior inferior cerebellar artery (PICA). The pons is supplied by paramedian and short circumferential branches of the basilar artery. Two major long circumferential branches are the anterior inferior cerebellar artery (AICA) and the superior cerebellar artery. The midbrain receives its arterial supply primarily from the posterior cerebral artery as well as from the basilar artery. The venous drainage of the spinal cord drains directly to the systemic circulation. By contrast, veins draining the cerebral hemispheres and brain stem drain into the dural sinuses. Cerebrospinal fluid also drains into the dural sinuses through unidirectional valves termed arachnoid villi. 

The systemic veins are derived from cardinal veins (CVs), which apart from umbilical and vitelline vessels are one of three main elements of foetal venous system. CVs in the form of paired structures located symmetrically on both sides of embryo s body appear in 4th week of gestation. System of CVs is comprised of anterior cardinal veins (ACVs) draining cranial parts of the body and posterior cardinal veins (PCVs) providing drainage from caudal parts. ACV and PCV join together into common cardinal vein - CCV (Cuvier ducts), entering the sinus venosus of early heart eventually. 

After venous access, some consideration should be given to the sequence of lead placement. Some operators prefer to place the RV electrode first for emergency RV pacing, should heart block ensue because the heart failure patients commonly have a left bundle branch block and any trauma to the conduction system or right bundle may result in complete heart block. Other operators choose to place the coronary sinus lead first and, if necessary, depend on heart rate support via a temporary transvenous pacemaker placed via the femoral vein. The issue of failure speaks for placing the coronary sinus lead first. Should the procedure fail with unsuccessful left-sided left ventricular lead placement and the patient has already received right-sided electrodes, a pacing system may be left without an indication unless a future second attempt is considered. As more and more systems are placed for a primary prevention indication like MADIT II, this has become less problematic (153). 

Coronary sinus lead placement was used many years ago but lost favor because of tbe high rate of lead dislodgmenL However, with the advent of CRT, placing a permanent lead in the coronary venous system has become... 

In patients being upgraded from an existing pacemaker or ICD to a CRT system, venous access and venous narrowing may hamper placement of the additional coronary sinus lead. One potential complication with difficult passage of a lead is venous perforation. In Fig. 18.36, the sheath used for introduction of the coronary sinus lead has perforated the vein, and dye was injected to determine the sheath position. The dye is shown in the mediastinum. In this patient, the sheath was withdrawn and redirected into the lumen of the vein, and the patient remained hemodynamically stable. 

---