Heart and great vessels:

Innominate (brachio-cephalic) veins.
 The right and left innominate veins are formed behind the sterno-clavicular joints by the confluence of the internal jugular vein and subclavian vein (Figure 1). In the early part of its course, the innominate receives the internal mammary, vertebral and inferior thyroid veins and on the left side, the superior intercostal vein. In patients with persistent left superior vena cava (PLSVC) the stem of the superior intercostal vein constitutes the upper part of the caval system (Figure 2). This can be important as a cause of difficulty with the left subclavian or left jugular approach to the central circulation 1 and as a cause of failed retrograde cardioplegia 2.

(Students of the obscure will also know that PLSVC is a feature of Raghib's syndrome 3 - which is characterised by the combination of abnormal drainage from a persistent left superior vena cava into the left atrium, the presence of an atrial septal defect and absence of the coronary sinus!!)

The right innominate vein runs vertically downwards behind the edge of the manubrium, whereas the left innominate vein passes at an angle of about 45 degrees across the superior mediastinum to join the right at the lower border of the first right costal cartilage (Figure 1).

The left innominate vein is covered anteriorly by the thymus or thymic remnant and is separated posteriorly from the trachea by the pretracheal fascia. The vein is occasionally intentionally divided (and subsequently reconstituted) during aortic arch surgery and for this reason the route of insertion of a CV or PA catheter should always be discussed with the surgeon before undertaking this kind of procedure.

Superior vena cava.
 The superior vena cava (SVC) is formed by the union of the innominate veins at the level of the first costal cartilage (Figure 3). It then courses vertically downwards, behind the right-hand border of the sternum, to enter the right atrium at the level of the third right costal cartilage. At the level of the second costal cartilage it is joined by the azygos vein which has arched forwards over the root of the lung. In about 0.3% of the population, a persistent left-sided SVC is also present (Figure 2).

Right Atrium.
 The right atrium is an elongated chamber which connects the superior and inferior vena cavae and which constitutes the right border of the heart (Figure 4).

In the context of pulmonary arterial catheterisation, the important anatomical features are the possible 'exit foramina' for a catheter. In the normal heart, these are: the tricuspid valve, the coronary sinus and the inferior vena cava.

The tricuspid valve has the largest cross-sectional area of all the cardiac valves and is vertically oriented (Figure 5). Thus the valve is on the medial wall of the atrium and it is for this reason that ventricular entry of a PAC is facilitated if the catheter is floated with its natural curve pointing to the nine o'clock position.

The coronary sinus lies in the posterior part of the atrioventricular groove and opens into the posterior wall of the right atrium between the tricuspid valve and the fossa ovalis. It is a wide-bore vessel, about 3 cm long, which carries about 60% of the myocardial venous return (predominantly from the left side of the heart). Two main veins open into it. The great cardiac vein, which drains the region supplied by the left anterior descending artery and the middle cardiac vein which accompanies the posterior descending artery. The coronary sinus can occasionally be inadvertently cannulated with a pulmonary artery catheter 4. This should be suspected if there is a gradual, rather than sudden, development of a 'right ventricular' trace during advancement of the catheter, or if there is paradoxical behaviour of the catheter such that balloon inflation produces a more pulsatile and deflation a less pulsatile trace (Figure 6).

The inferior vena cava opens into the 'floor' of the right atrium. At the atrio-caval junction, there may be a ridge of tissue - the remnant of the valve of the inferior vena cava, which tends to prevent inadvertent passage of a PAC down the IVC. This remnant is clearly seen in Figure 7.

Right Ventricle.
 The right ventricle projects to the left of the right atrium from which it is separated by the tricuspid valve. The ventricle has a complex crescentic shape and is lined by a series of ridges or 'trabeculae'.

With regard to pulmonary arterial catheterisation, the two important anatomical features of the ventricle are the orientation of the ventricular cavity and the position of the ventricular conducting system.

The cavity tapers upwards as the 'right ventricular outflow tract' towards the pulmonary valve. The valve is the most cephalad and anterior of the four cardiac valves, consequently, flotation of a 'lighter than blood' catheter from the ventricle to the pulmonary artery is most likely to occur if the patient is placed in a slightly head-up posture (Figure 5).

The conducting system of the heart has important relationships with the right ventricle. The bundle of His passes from the atrio-ventricular node, which is situated just above the coronary sinus in the interatrial septum, to cross the atrio-ventricular ring and enter the interventricular septum. From here it passes along the inferior border of the membranous septum to the muscular septum where it divides into the right and left branches. The right bundle is in a subendocardial position on the right side of the septum and is susceptible to pressure from the tip or shaft of a PAC. As a result, transient right bundle branch block occurs in about 3% of patients during catheter insertion 5 and complete heart block may occasionally complicate the procedure in patients with pre-existing left bundle branch block 6.

Pulmonary Artery.
 The main pulmonary artery runs upwards from the pulmonary valve for a distance of 3 - 4 cms before it bifurcates in the concavity of the aortic arch into the right and left pulmonary arteries. Most PACs enter the right pulmonary artery 7, thus, in their intrathoracic course, they will come to completely encircle the aorta (Figure 8).

References:
1. Lai YC, Goh JCY, Lim SH et al Difficult Pulmonary Artery Catheterization in a Patient with Persistent Left Superior Vena Cava Anaesth Intensive Care 1998; 26: 671-673

2. Shahian DM Retrograde coronary sinus cardioplegia in the presence of persistent left superior vena cava. Ann Thorac Surg, 54:1214-5, 1992 Dec

3. Okumori M, Hyuga M, Ogata S, Akamatsu T, Otomi S, Ota S Raghib's syndrome: a report of two cases. Jpn J Surg 1982;12(5):356-61

4. Baciewicz FA, Nirdlinger MA, Davis JT An unusual position of a Swan-Ganz catheter. Intensive Care Med 1987;13(3):211-212

5. Sprung CL, Elser B, Schein RMH, et al Risk of right bundle-branch block and complete heart block during pulmonary artery catheterization. Crit Care Med 17:1-3, 1989.

6. Shah KB, Rao TLK, Laughlin S, et al. A review of pulmonary artery catheterization in 6245 patients. Anesthesiology 61:271 - 275, 1984

7. Benumof JL, Saidman IJ, Arkin DB, et al: Where pulmonary artery catheters go: Intrathoracic distribution. Anesthesiology 46:336, 1977

Last edited on: 12/11/2000