In our observational study of levophase of coronary angiograms, we analysed coronary venous anatomy for the purpose of cardiac resynchronization therapy (CRT) LV lead placement. Coronary sinus lead placement for resynchronisation therapy is required at all ages, and younger patients of dilated cardiomyopathy are a common subgroup. There is no sex predilection for dilated cardiomyopathy. In our study the median age was 56 years. Sex ratio was 2.5:1 (male:female). Age and sex distribution of the study is characteristic of the patient population seeking treatment at our tertiary care centre. This phenomenon is known to skew data of studies conducted in developing countries. There is a strong referral bias; female patients are more likely not to reach a tertiary care centre for treatment. The sex ratio in similar studies carried out in the western countries were 0.8:1 in a study of retrograde balloon occlusion venography by Mischke et al, and 1.2:1 in a study of levo-phase coronary angiograpy by Gilard et al[11,12]. Similarly there was no gender bias in anatomical studies of the coronary venous anatomy on human cadavers.
Nearly all cases in our study underwent coronary angiography for the evaluation and treatment of coronary artery disease. Only 11 patients had severe LV dysfunction which is present in all cases requiring CRT. Although the branching pattern can be assumed to be unaffected by the development of cardiomyopathy, there can be significant change in angle of opening of coronary ostium in cases with significant enlargement of left heart and normal sized RA and RV. Our study had too few cases of cardiomyopathy to be able to detect such a difference. The coronary sinus was adequately visualized in all cases. The borders were sharply delineated in a majority (visibility scale 3 in 74%). In the rest of the cases the borders were hazy but sufficient for the purpose of guiding the planning of LV lead implantation. Surprisingly, obesity (BMI) did not affect visibility. Because we obtained the CS anatomy in levophase in patients undergoing coronary angiography only in two views without any extreme angulation, insignificant amount of additional radiation exposure was anticipated.
The visibility of the venous system in our study was comparable to that attained by 360 slice CT study conducted by Chunjuan Sun et al. In our study we identified a separate opening of the PLV into the RA in 1 case, and a suitable PLV opening close to the CS ostia in 6 cases. These are visualized better antegrade than retrograde as selective hooking will cause them not to be opacified. Meisel et al in their study on retrograde CS venography obtained optimum anatomical information in 67% of cases, compared to 92% in our study.
It is believed that retrograde occlusive venography better visualises the CS anatomy but it has its own lacunae. Some physicians use hyperaemic agents to aid visualization of CS in levophase. Arbelo E et al compared occlusive retrograde venography with hyperaemic venous return angiography (levophase of coronary angiography). They used 200 µg of intracoronary Nitroglycerine or 60 µg of Adenosine to increase the coronary flow and thus the venous return in coronary sinus. The anatomical information obtained by both methods was adequate (100% vs 97.5%, respectively). Although occlusive retrograde venography is the most co mmonly employed technique, it has its own drawbacks. First, in the absence of venous anastamoses, veins with a posterior origin may not be visualized. Sometimes balloon does not provide a completely occlusive barrier, and 2 injections (distal and proximal) are then required to highlight the venous anatomy. In addition, for the opacification of the AIV, contrast medium has to be injected with the balloon inflated more distally in the GCV. This may lead to complications such as dissection of CS and heart blocks.
Levo-phase radiological anatomy
We utilized 2 orthogonal views viz. LAO Cranial (40°, 30°), and RAO Cranial (30°, 30°) to view the Coronary Sinus. The LAO Cranial view showed the coronary ostia clearly. This view visualizes the proximal portion of CS without foreshortening and we can also see its angulation with main body of CS. Posterior vein, PLV, lateral vein were also well differentiated in this view along with the take-off angle of the PLV with the body of the CS. However, the distal portion of the Coronary Sinus was foreshortened in this view, making it hard to differentiate an anterolateral vein from an AIV. Presence of a thebesian valve was detected by noting an upward direction of the outflow jet into the RA. The inferior border of the outflow is smooth. We found evidence of a thebesian valve in 21 cases. An obstructive thebesian valve may require an Amplatz guiding catheter to cannulate the CS ostium. Mischke K et al in their study of coronary venous anatomy found evidence of a thebesian valve in 11 out of 100 cases. These figures are much less than those found in anatomical studies carried out by Randhawa et al (thebesian valves seen in 50 dissections) and by Noheria et al (309 valves seen in 643 dissections). Small sized valves visible on direct examination are of little clinical significance[15,16].
RAO cranial view showed the ostia and the proximal portion of the CS end on. The proximal portion was however foreshortened. Posterior indentation of the proximal portion of the CS before joining the main CS body was studied in this view. We found this in 5 (3%) of 164 cases. This view was most useful for showing the length of the vein, from the base of the heart (AV groove) to the apex. In our study, we divided this base to apex distance into 3 equal lengths: Proximal, mid, and distal; 81% of the PLVs extended upto the distal one third.
In some cases, the coronary venous anatomy could also be seen in other views taken during the study. The RAO caudal view was very useful in showing the branches of the MCV, which were not visible in our 2 cranial views. Having more views also helped in showing the PLV in greater detail. More bends could be seen when more views were available.
The optimal site for LV lead placement is the posterior lateral wall of the LV. Of the 164 patients in our study, 151 (92%) had a suitable vein draining the posterior lateral wall of the LV. In 112 cases this was the PLV; in another 39, other veins drained this area. A critically stenosed LCX or a super-dominant RCA were strongly associated with failure to visualize an adequate vein. In one case in which the PLV was not visualized, the patient was found to have an anomalous LCX. If dye had been injected into this anomalous vein (instead of into the LAD) a PLV would probably be seen. The PLV opacifies if dye is injected into the region (posterior lateral wall of the LV) that it drains. In most cases the artery supplying the area drained by the PLV is the LCX, in some it is a super-dominant RCA. If the LCX has flow limiting stenosis, an anomalous origin, or if there is a super-dominant RCA, the posterior lateral part of the LV does not recieve enough dye and likely remains hidden.
We found 4 cases with a very large MCV or AIV (6 mm). Patients without a PLV were found to have on an average 1.5 mm larger MCV than patients with a visible PLV (P > 0.05). The AIV was found to be on an average 0.7 mm larger in cases without a PLV, compared to cases with a PLV; but this did not reach statistical significance. An absent PLV was found in 52 cases in our study. In 39 of these cases, there was another vein supplying the posterior-lateral wall of the LV. The number of cases in which the PLV is absent is far greater in our study than in a similar study using levo-phase coronary angiography by Gilard et al or in the anatomical studies on human cadavers by Randhawa et al and by Noheria et al. We did not count small veins (unsuited for CRT LV lead placement) in our study. Veins with a diameter of > 2 mm measured 2cms distal to its ostium were considered favourable. The larger number of cases with no PLV seen in our study, is explained when this is considered. When a PLV was present, it was generally straight with 62% having no bends. The take-off angle was generally favourable, with an unfavourable take-off seen in only 7% patients.
Non availability of a suitable branch draining the lateral or posterior LV wall is an indication for epicardial lead placement by thoracotomy. In our study, we were unable to visualize an adequate vein in 13/164 cases, although the number of cases in which it is truly absent may be lower.
We evaluated only 2 levo-phase views of left coronary angiograms in our study. Use of more views may better identify the venous anatomy. We did not study the venous tree in right coronary angiograms. Although this is not required in most cases, our study shows that visualization from left injections is poor when circumflex territory is not perfused by the left coronary artery. The technique increases total quantity of dye, and radiation during coronary angiogram, and this may be significant in very sick patients in poor general condition. We excluded such patients from our study.
We did not compare our results with retrograde occlusive venography because it may increase the contrast and radiation dose. We also did not use a hyperaemic agent (e.g., nitroglycerine or adenosine) to increase coronary flow and resultant venous return in CS as used in some studies because it might cause hypotension and/or bradycardia in some patients. In addition, adenosine use may not be feasible in patients with bronchial asthma and severe obstructive pulmonary disease.