Another device was a 7-Fr balloon-tipped catheter (7 F, single lumen; Arrow Int, Reading, PA)  used by Diab et al (Figure 16 ). After accessing the CS through either right femoral or left subclavian veins and before contrast injection, the balloon was inflated by air to obstruct the CS and contrast aspiration was performed using a syringe. In order to determine the volume of extracted contrast, reduction of patients’ blood Hct from Hct levels in CS blood was calculated and the result was divided by the patients’ Hct. Finally, the result of this equation was multiplied by the volume of aspirated blood from the CS. All the procedures are done without any failures. However, direct CS cannulation was just performed successfully in six patients and CS quadripolar or decapolar catheters were used to help cannulation in the remaining 12 individuals. Contrast aspiration was performed through a balloon-tipped catheter in 10 patients or direct extraction from the sheath in the other eight participants. Although patients who underwent CS contrast removal through the balloon catheter had remarkably higher time to clearance of the contrast compared to the direct aspiration group, the fraction of extracted contrast was not significantly different between groups. The possible mechanisms for shorter contrast clearance time in those undergoing CS contrast extraction via the sheath might be associated with the faster rate of aspiration and wider sheath caliber. Also, the sheath tip has a lower probability of collapsing or facing the vessel wall during the procedure and it also creates a more negative suction pressure. They suggested the possible safety of CS cannulation using trans-septal sheath due to its favorable curves and proper manipulation and rotation with or even without dilator support. They also claimed the simplicity of this method as well as its cost-effectiveness without the requirement of advanced technologies. Despite their suggestion for optimal choice between balloon catheter or direct sheath is defined by CS caliber in relation to the sheath, complementary studies are required. Their potential concern on CS obstruction on limitation of coronary arterial blood flow might be explained by reactive hyperemia leading to increased microcirculation after balloon deflation. Additionally, this enhanced coronary transit time in the context of CS occlusion might be associated with decreased necessary contrast volume (93).

Although the safety and feasibility of CS contrast removal have been indicated in several animal and human studies and this procedure is quite accessible in most clinical settings, there are still some possible challenges that should be considered. Despite its rareness, CS anatomical abnormalities are one of the culprits in this regard. CS length of less than 20 mm is considered to be short CS and might be associated with difficult CS cannulation (97–99). Also, the CS can be varied from enlarged to hypoplastic or even absent in a few individuals. CS enlargement could be either primary or secondary to other pathologies including unroofed CS, interrupted inferior vena cava, coronary artery fistula, and total or partial anomalous pulmonary venous return. The former abnormality is a unidirectional left to right or a bidirectional shunt between the left atrium and superior segment of CS (99,100). Also, CS manipulation during catheterization or contrast aspiration might be associated with CS trauma or thrombosis, or ectopia of atria or ventricles (90). It seems CS morphology and proper catheter placement might play pivotal roles in successful cannulation and should be individually assessed. Moreover, blood loss per coronary injection might be considerable. Danenberg et al. reported aspiration of 12-16 ml of blood per injection (90). This was 16.6 ± 3.23 ml per injection in Diab et al.’s study. Also, post-procedural hemoglobin was slightly lower in the CS group in the aforementioned study, but it was statistically insignificant (10.85 ± 1.3 g% vs. 11.62 ± 1.3 g%, P= 0.06) (93).

Patient discomfort, unstable sheath position, and difficulty in advancing the sheath to the CS ostium have been reported to be some difficulties during CS cannulation (100). Another study reported an approximate 10% of minor myocardial damage during CS catheter placement, but all complications were not clinically evident (97). Another considerable factor might be attributed to CS cannulation time which has been reported in different ranges. The time was 19.27 ± 3.54 minutes in one study compared to 11.1 ± 9.3 minutes in another one (80,93). The equipment, the procedure (angiography versus intervention) as well as skillfulness of the interventionist might be some possible explanations for these reported differences.

Contrast extraction from CS seems to be a novel method ultimately leading to a decrease in CIN incidence among CA/PCI patients. However, some questions are currently needed to be investigated by further comprehensive studies. For instance, despite PCI or CA being common in origin, the required time for completion of each method is quite different. Acceptable catheter sheath size should also be more investigated. Appropriate training for proper CS manipulation should also be considered. The blood loss amount is another potential concern that needs to be evaluated and probably corrected by returning the aspirated blood without contrast media to the patient. Normal blood loss during conventional CA should be less than 300 cc  (86). Moreover, studies are probably necessary to define the exact CS contrast aspiration time to prevent CIN.

CIN in the context of CA and PCI is a major concern. Despite several proposed methods to prevent CIN, CIN occurs in high rates with high morbidity and mortality. New means that can reduce CIN is desirable. Contrast removal from CS has been shown to be such a mean with future potential in order to decrease CIN risk during coronary procedures with a great safety profile. Large randomized trials are required to assess the efficacy and safety of this approach.

Competing interests : Mohammad Reza Movahed has the Patent holder for the contrast removal device.