Introduction

Catheter is a hollow tube with one end having port to connect to the pressure monitor or to pass a thin caliber wire through it and other end being soft and hollow to engage or pass it into an artery or structure. Micro means actually very small, but it is used here to denote small catheter as they are very low in profile. These catheters are 2 to 2.5F in diameter and lengths vary from 100cm to 150cm. The wall may be made of polyethylene or could be reinforced with coils or braded within the wall for better support, push ability or to make them kink resistant. The tip of the micro catheter has a radio opaque marker. Even though there are varieties of microcatheters used in interventional cardiology such as angiography microcatheter (to inject contrast or medicine or embolic materials or perfusion to distal bed), access microcatheters (small vessel or super selective anatomy for diagnostic and interventional procedures), guiding microcatheters, and next-generation fractional flow reserve microcatheter technology, this review mainly discusses about percutaneous coronary intervention (PCI) microcatheters.

Types of Micro Catheters

1. Single lumen micro catheters1: mainly used for crossing support and distal injections

2. Dual lumen micro catheters2 3: mainly used for guidewire placements and exchanges, parallel wire or buddy wire after complex channel crossing, for angulate side branch wiring, and to avoid tangling of the guidewires.4

Functions of Micro Catheters

Multiple ways to use the microcatheters in different interventional scenarios are described.5

1. Forcomplex chronic total occlusion (CTO) antegrade approach: increases wire support and penetration force, makes parallel wire and sea saw techniques easier and allows wire exchanges easy.

2. For complex CTO retrograde approach: increases the wire support and accesses the collaterals with latest generation wires.

3. Forcomplex tortuous distal lesions: provide better support to the guidewire to go more distally and make exchange of guidewires quicker.

4. Bifurcation PCI with or without acute side branch: side branch access made easier especially with twin lumen catheters and with steerable tip micro catheters.6

5. Distal vessel assessment with contrast injections and also to deliver the drugs distally into the vascular bed and myocardium. However, we need to exercise caution to de-air the catheter properly and also make sure that the catheter tip is in the true lumen and not in the dissected plane. When blood is seen at the hub of the microcatheter with or without very gentle aspiration, it confirms the distal correct luminal position of the catheter.

6. In future, these could become useful in making intracoronary imaging more trouble free (in pipe line research to enable placement of imaging catheter distally).

The above-mentioned function that is injecting contrast is used in microcatheter-facilitated primary angioplasty in ST-segment elevation myocardial infarction to do direct stenting and achieve effective thrombolysis in myocardial infarction (TMI) 3 flow distally.7 Similarly, microcatheter distal perfusion technique can be used in bail out coronary erfusion.8

Varieties of the Microcatheters

Most commonly used coronary MCs5 are Corsair and Corsair Pro (Asahi Intecc, Aichi, Japan), Caravel (Asahi Intecc), Finecross (Terumo, Somerset, NJ, USA), and the Turnpike family: Turnpike, Turnpike LP, Turnpike Gold, and Turnpike Spiral (Teleflex, Wayne, PA, USA). The details of mostly available catheters with their details are mentioned in Table 1. With tornus catheter, screwing technique (torquing and retorquing) is used to advance the microcatheter, which is improvised to corsair now9. Most of the microcatheters has a single radiopaque marker at the tip but Fineduo microcatheter has two radiopaque markers facilitating the access of side branch or collateral or the distal most stent strut.

Recent Microcatheters

Now, the next generation of corsair, corsair Pro XS with more trackability is available. Navitian (iVascular, USA) microcatheter is specially design to navigate the CTO lesions due to the internal and external conical transition.

Uses and Causations during Usage of the Microcatheters

The specific advantage of Corsair and turnpike is to torque and thread the microcatheter in tough and tortuous lesions. This is because of their tapered and low profile tips along with bradding. However, one should be careful in calcific lesions while using corsair. In mild calcification at lesion site or in the artery, the corsair can be used, but in heavily calcified lesions, entrapment of corsair can occur. The caravel and fine cross micro catheters are used generally to push the catheter over the wire without torqueing when the arteries are softer and relatively without much coils. The contrast injection and drug delivery are better in fine cross due to better lumen inside. The steerable tip and twin lumen catheters (Table 2) are obvious choice for bifurcation PCI to access the angulated side branches. Also, 150 cm length corsair is used for exteriorization of the coronary wire during retrograde CTO technique. Comparison characteristics of a few microcathetersthat are steerable and angle tip are mentioned in Table 3.

Complications of Micro Catheter Usage

According to Megaly et al's study, the most common complication of the micro catheter usage is tip fracture and the guidewire getting stuck in the lesion and the most commonest clinical consequence is procedure abandonment and surgery and very rarely perforation and death10 (Table 4).

Conclusions

Coronary micro catheters are essential tools in today's era of contemporary complex PCI. They have significant utility in CTO PCI and are mandatory for retrograde CTO PCI. The operators need to be aware of the various types of micro catheters available and know the advantages and specific scenarios in which each one could be preferred. It is also important to know how to use them carefully to avoid complications during PCI.