Thebesian Sinusoids of Special Structures

Sinusoids are large capillaries with different morphologies. They are remnants of the primitive cardiac circulation ⁹ (Fig. 19‑4).

Conduction System

Both atrioventricular and sinoatrial nodal zones are sinusoid rich for retrograde blood flow to nodal conducting tissue ¹⁴ in case the arterial supply is compromised.

Papillary Muscles

The papillary muscles are mainly drained by the SVC in the RV and by the great cardiac vein (GCV) and SVC in the left. ⁶ Retrograde vascularization by sinusoids can supplement normal flow to papillary muscles and may prevent their rupture after ischemic damage. ¹⁵ Thebesian vessel foramina are common at the apex of the ventricles and at the base of the papillary muscles (Fig. 19‑5).

Left Ventricle Venoluminal Thebesian Vessels

A greater number of Thebesian veins are seen in the RV than in the LV. ¹⁰ Arterioluminal vessels are identified only in the RV, whereas venoluminal vessels are present in both ventricles.

Veins of the Left Atrial Wall

The majority of the left atrial (LA) veins are tributaries of the greater CVS. Three groups are described ^{6 ,​ 8} :

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  Veins of the posterior and lateral walls of the LA empty into the CS and GCV (Fig. 19‑6).

  
  
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  Septal veins of the LA drain into the RA through the interatrial septum. These veins are commonly seen with CT angiography (CTA). Veins anterosuperior to the fossa ovalis pass through the interatrial groove and empty into the right atrium near the superior cavoatrial junction (Fig. 19‑7). Some (12%) may pass through the superior interatrial muscle connections where Bachmann’s bundle is located ¹⁸ (Fig. 19‑8). Veins inferoposterior to fossa ovalis are less common (Fig. 19‑7).

  
  
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  The posterosuperior wall of the LA near the LA appendage drains into the LA and the superior pulmonary veins (Fig. 19‑7). They may connect mediastinal veins, azygos, or hemiazygos venous system, and the bronchial veins. ⁸ The mediastinal connections can be an important alternative route for venous return to the atria in case of occlusion of the pulmonary vein, brachiocephalic vein, or SVC (Fig. 19‑7 , Fig. 19‑9). In congenital atresia of the CS, the myocardial venous drainage can be via ectatic atrial veins of the LA. ¹⁹

  

  

  

  

Veins of the Right Atrial Wall

Majority of the right atrial wall veins are located intramurally and drain into the RA. The veins draining the wall of the right atrial appendage have no connection with the epicardial veins, and therefore are classified as smaller CVS. The RA veins are classified into four groups based on anatomical locations (Table 19‑1):

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  Small intramural venous tunnels draining directly into the RA. They are a few millimeters in length and 1 mm in diameter. ⁶

  
  
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  Venous tunnels of the RA (the sinus coronaries atrii dextri or right atrial CS): Termination of the anterior cardiac veins of the RV is variable. They may drain directly into the RA, small cardiac vein, or in some into a venous tunnel. ⁶ When it exists, this venous tunnel runs parallel and 1 to 2 cm above the tricuspid orifice along the posterior or posterolateral wall of the RA ²⁰ (Fig. 19‑6). In high-quality CTAs, these veins may be partially visible (Fig. 19‑6 b).

  
  
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  The sinoatrial node region has sinusoids draining into the RA. ¹⁴ This network of anastomosing blood vessels potentially can protect the node in case arterial supply is compromised. However, this phenomenon is rare given the common variants of dual or multiple arterial supplies to the node.

  
  
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  Atrioventricular node region: Venous tunnels are seen at the base of the interatrial septum near the atrioventricular node and the bundle of His and usually open into the RA near the ostium of the CS or directly into the CS (Fig. 19‑6 , Fig. 19‑7). These tunnels can be seen in CTA and should not be confused with anomalous vessels or a patent foramen ovale.

Anterior Right Ventricle Venous System

Including the anterior cardiac, right marginal, and conus veins are seen in 90% of cases ^{6 ,​ 20 ,​ 21} (Table 19‑2). The anterior cardiac veins drain two-thirds of the RV including the anterior and anterolateral walls of the RV. These veins are frequently seen in coronary CTAs (Fig. 19‑10). They are variable in sizes and numbers and usually drain into the RA above the atrioventricular groove. ^{6 ,​ 16 ,​ 21 ,​ 22} In 5 to 27%, they merge to form a common trunk before entering the RA. ^{6 ,​ 21} The right marginal vein originates near the right ventricular apex and receives branches from posterior and anterior surfaces of the RV (Fig. 19‑10). In one-third of cases, the vein continues as small cardiac vein into the CS. ⁶ In the remainder of cases, it drains into the RA or the venous tunnels of the RA.

Table 19.2 Characteristics of the epicardial veins of coronary sinus and anterior right ventricle venous system

Veins	Origin	Territory	Ostial diameter (mm)	Frequency (%)	Drainage	Number	Variant	Ostial valve (%)
CS	GCV	Left atrioventricular groove	4–14 10	99	RA	1, duplication is very rare	Absence (with left SVC), unroofed, atresia (1%), duplication	80
GCV/AIV	Apex	Anterior septum, anterior of both ventricles, parts of LA and apex	AIV = 0.9–4.4 (2.7), GCV = 1.2–6.3 (3.9)	100	CS (99%)	1 (98%)	Aberrant course to RA in 1%, aneurysm, myocardial bridge 2–8%, duplication 3%, myocardial belt (6%)	85
IIV	Apex	Posterior wall of the RV and LV, apex, posterior two-thirds of the interventricular septum	2–5.3 (3.6)	100	CS, rarely RA (2.5%)	1 (75%), 2 (24%)	Aneurysm (8%), varicoid, duplicated, myocardial cover (2.5%)	60
LPV	Posterior wall	Lateral and diaphragmatic walls of the LV	1–5.5 (2.4)	95	CS (37–77%), GCV (13%)	1 (63%), 2 (23%), multiple small (9%), non (5%)	Bulbar (5%), myocardial cover (2%)	30
LMV	Posterolateral wall of LV	Draining much of LV myocardium	1–3 (2.2)	70–85	GCV (80%), CS (20%)	1	Absence common	30
SCV	Right atrioventricular groove	Diaphragmatic surface of RV	<1	30–50	CS (85%); IIV (12%)	1	Can receive the right marginal vein in 10%	–
OVM	Junction of CS and GCV	Posterolateral LA, 2–3 cm in length	0.4–1.8	85–95	CS	1	Persistent SVC 0.5%	–
RMV	Apex	Anterior and posterior RV walls	0.5–3	13–80	SCV (30%), rest RA or tunnel of RA	1	Large draining into a vertical RA tunnel	–
ACV	Anterior RV	Anterior and anterolateral RV	0.5–1	90	RA (30%), venous tunnel of RA (66%), SCV	1 (24–57%), 2 (33–48%), 3 (9–28%), up to 15 tiny ones	Abnormal course of AIV into SVC, large conus vein	12
Abbreviations: ACV, anterior cardiac vein; AIV, anterior interventricular vein; AV, atrioventricular; CS, coronary sinus; GCV, great cardiac vein; IIV, inferior interventricular vein; IVC, inferior vena cava; LA, left atrium; LMV, left marginal vein; LPV, left posterior vein; LV, left ventricle; OVM, oblique vein of Marshall; RA, right atrium; RMV, right marginal vein; RV, right ventricle; SCV, small cardiac vein; SVC, superior vena cava. Source: Data from von Lüdinghausen, 5 ,​ 6 ,​ 33 Pina, 21 Mierzwa and Kozielec, 22 Ortale et al, 30 Pejkovic and Bogdanovic, 32 Saremi et al, 35 and Cendrowska-Pinkosz. 41

The conus (infundibular) veins are usually small veins and drain into the RA. However, they can be large and varicoid (i.e., arteriovenous fistula) creating diagnostic problems (Fig. 19‑11) or causing excessive bleeding during surgery. Veins of Zuckerkandl and Cruveilhier are described in the anatomic literature for veins draining the anterior and posterior surfaces of the infundibulum, respectively ^{20 ,​ 21} (Fig. 19‑11).

Imaging Methods

The CS is frequently used as a conduit for catheter treatment of arrhythmias as well as left ventricular pacing. These procedures are well known for their potential technical difficulties. As a result, different imaging methods are introduced for evaluation of this system. Each technique has its own advantages and limitations. ^{23 ,​ 24 ,​ 25 ,​ 26 ,​ 27 ,​ 28 ,​ 29}

Retrograde venography via the CS is currently the standard technique for defining the CS anatomy; however, it is invasive in nature and can be technically challenging. This technique is frequently used to show the anatomy of the CS and target veins for CRT. In this technique, using an occlusive balloon, contrast is injected into the CS and two orthogonal views including right anterior oblique 45 degrees and left anterior oblique 45 degrees are obtained. ²³ High-speed rotational coronary venography uses rapid isocentric rotation over a 110-degree arc in 4 seconds, acquiring 120 frames per angiogram. ²³ With this modification, vessel overlap and foreshortening will be reduced and target veins including second-degree tributaries can be better defined.

Levophase of coronary angiography is preferred by some investigators and claimed to better define the anterior (superior) interventricular vein (AIV) and IIV as well as the peripheral branches compared to retrograde venography. ²⁴ The technique takes advantage of the coronary artery angiography procedure commonly indicated in the assessment of candidates for CRT.

Magnetic resonance imaging (MRI) and CT have been increasingly used to assess anatomy of the coronary vessels including coronary veins. ^{25 ,​ 26 ,​ 27 ,​ 28 ,​ 29} CT has the advantage of showing part of the CS and in some cases the origin of the IIV, which will be obscured with balloon in retrograde venography. With CT, there is no foreshortening or vessel overlap. CT also demonstrates many ancillary structures such as coronary arteries, old infarctions, interatrial septum anatomy, and variants of the normal anatomy. Higher radiation dose in CT is a limitation ²⁶ that can be modified using dose reduction techniques. CT also may have difficulty showing second-order tributaries of the coronary veins in routine coronary CTAs. Demonstration of the oblique vein of LA is also more challenging with CT compared with retrograde venography. However, with some modification of the CT technique, most small branches can be nicely depicted. ¹⁸

Great Cardiac Vein

The GCV is the longest and the most consistent vessels making up the cardiac venous system, almost always entering the CS. ^{30 ,​ 31 ,​ 32 ,​ 33 ,​ 34} This vein drains blood from the anterior interventricular septum, the anterior surfaces of both ventricles, part of the LA, and the apical region of the heart. ⁶ The AIV portion of the vein courses superiorly within the anterior (superior) interventricular groove (sulcus) and then enters the left atrioventricular groove where it is defined as the GCV. The GCV may originate at the apex or in the apical or middle third of the anterior interventricular groove with a highly variable position with respect to the left anterior descending (LAD) artery, which may render very difficult the localization of the latter especially in coronary artery bypass procedures.

The GCV crosses the branches of the left coronary artery system including the anterior descending and the circumflex branches forming a triangle ^{6 ,​ 30} in which the vein is mainly superficial to arteries in 60 to 70% ^{31 ,​ 32 ,​ 33 ,​ 34} of cases (Fig. 19‑13). Branches of the left coronary artery system traverse this triangle (i.e., the ramus intermedius). However, it is important to know that the relation of the vein and these arteries is highly variable and practically unpredictable in many cases.

Aberrant drainage of the GCV into the RA or SVC is described. ³³ In this situation, the GCV runs in the transverse sinus and finally joins the azygos vein or the RA. Knowledge of this anatomy prior to surgery can be important for RCP.

Myocardial bridges are detected above the AIV or its tributaries in 8%. ³⁰ Aneurysmal dilatation of the distal end of the GCV has been reported and may interfere with coronary artery bypass grafting (CABG). ³⁴ It is the second most common location of coronary vein aneurysm seen in 1.5% of CT examinations ³⁵ (Fig. 19‑14).

Inferior Interventricular Vein

The IIV, also known as middle cardiac vein or posterior interventricular, travels along the inferior aspect of the heart (attitudinal orientation) in the interventricular groove. The vein is a constant landmark and drains into the CS approximately 1 cm from the CS ostium. Extending from the apex to the CS, it drains the interior walls of the ventricles as well as the apical area and the posterior two-thirds of the septum ⁶ (Fig. 19‑15). The terminal portion of the vein measures 3 to 4 mm in diameter and appears angled in 35% or bulbous in 19% of population. ⁶ Fusiform aneurysmal dilatation (focal dilatation of twice the normal diameter; mean; 10.5 ± 1.4 mm) of the venous confluence is reported in CT studies in 8% (Fig. 19‑15). It is the most common location for bulbous enlargement of the coronary veins. ³⁵ Aneurysms, especially the diverticular form, arising from the CS and the confluence of coronary veins with the CS, may be associated with cardiac arrhythmias such as ventricular preexcitation. ^{36 ,​ 37}

Left Posterior (Posterolateral) and Left Marginal Veins

Several venous branches drain the myocardial walls located between the IIV and the AIV. ³⁰ Veins draining the posterior and lateral walls of the LV are of particular interest for the LV pacing in CRT ³⁸ (Fig. 19‑16). Imaging techniques permit identification of potential anatomic factors that may pose difficulties to cannulate and advance the LV pacing lead including ostial valves, variceal veins, or absence of the posterior or lateral vein.

The left posterior (inferior) veins are one to three in numbers and measure 2.5 mm at ostium. While the distal myocardial origin of the left posterior vein is highly variable, it usually terminates in a uniform fashion in the CS (75%), although it can also drain into the GCV. ^{6 ,​ 32 ,​ 39} It is single in 60%. In the absence of the left posterior vein (5%), it is the left marginal vein that drains most of the left ventricular posterolateral wall. ⁵ Small diameter of the vein (<2 mm) and acute angulation with the CS may complicate the insertion of the lead for CRT. ³⁸

The left marginal (obtuse marginal) vein is present in 70 to 95% of specimens, emptying into the GCV in 80% of cases and into the CS in the remaining. ³⁰ The frequency of visualization is less with CT or MRI compared with retrograde venography. ^{25 ,​ 26 ,​ 27 ,​ 28} It drains much of the LV myocardium, usually running superficial to the marginal branch of the circumflex artery. ^{32 ,​ 40} Its diameter varies and, like other coronary veins, is enlarged in patients with cardiac failure. ⁴⁰ Anastomosis of the epicardial veins in the periphery is common. This is especially common between the veins of the LV such as between the GCV and posterolateral vein or between the IIV and posterolateral or marginal veins (Fig. 19‑12).

Small Cardiac Vein

With a frequency of 30 to 50% and average diameter of 1 mm, the small cardiac vein (right coronary vein) drains the posterolateral wall of the RV into the CS (85%), the IIV (12%), or rarely the RA (1%) ^{16 ,​ 30 ,​ 41} (Fig. 19‑12). It is more common in women than in men. ⁴¹

Oblique Vein of the Left Atrium (Marshall)

The oblique vein of Marshall (OVM), a remnant of the left SVC, descends along the lateral and inferior walls of the LA between the LA appendage and the left pulmonary veins and joins at the junction of the GCV and the CS approximately 3 cm from the CS ostium. ^{42 ,​ 43} The vein is short (2–3 cm in length) and its superior part obliterated by fibrosis. Complete fibrosis or obliteration in the form of a cord is seen in 5 to 12%. ⁶ The average diameter is 1 mm (0.4–1.8) and the angle with the CS varies between 25 and 50 degrees. It is present in 85 to 95% ⁴² of cases (Fig. 19‑16). Balloon-occluded venography of the CS can visualize the OVM in 73% of the patients. ⁴⁴ Demonstration of this vein with CT requires special attention to the detail and quality of the CTA. It is reported in 35 to 40% of cases ^{25 ,​ 39} (Fig. 19‑15 c, Fig. 19‑16 a). The best phase for visualization of the OVM is ventricular systole, likely due to coronary vein enlargement during this phase. ³⁹

The OVM is now implicated as a source of activation in atrial tachyarrhythmias. ^{45 ,​ 46 ,​ 47 ,​ 48 ,​ 49} This may originate from the muscle sleeve of the vein (Marshall’s bundle). ⁵⁰ This muscle sleeve is connected to the musculature surrounding the CS or the left pulmonary veins ^{45 ,​ 46 ,​ 47} (also see section “Coronary Sinus Interatrial Muscle Connections”). The vein is of greater significance when it persists as a patent left SVC. It is seen in 0.5% of the normal population and up to 5% of congenitally malformed hearts ⁵¹ draining into the CS.