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

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

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

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.

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

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

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

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.

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.

Table 1

Description of different microcatheters (courtesy of city today website)

Company name

Product name

Type of catheter construction

Proximal size (F)

Middle size (F)

Distal catheter

size working

(F) length (cm)

Catheter endholeID (inch)

Recommended guidewiresize (inch)

Radiopaque tip (Yes/No)

Hy Coat

drophilic ing (Yes/No)

Acrostak

M-Cath

Stainless steel covered with blue Teflon (PTFE)

2.1

2.1

2.25

135

0.016

0.014

Yes

Yes

Asahi Intecc USA, Inc.

Asahi Caravel

Stainless steel braided

2.6

1.9

1.4

135, 150

–

0.014

Yes, tungsten powder 5-mm tip

Yes

Asahi Intecc USA, Inc.

Asahi Corsair/Corsair Pro

Stainless steel braided

2.8

2.6

1.3

135, 150

–

0.014

Yes, tungsten powder 5-mm tip

Yes

Asahi Intecc USA, Inc.

Tornus

Stainless steel braided

3.3

2.1

1.8

135

–

0.014

Yes

No

Asahi Intecc USA, Inc.

Tornus 88 Flex

Stainless steel braided

4.1

2.6

2.1

135

–

0.014

Yes

No

Baylis Medical Company, Inc.

ProTrack Microcatheter

Coiled stainless steel, PTFE, Pebax

2.7

2.7

2.7

145

0.022

Up to 0.021

Yes

No

Baylis Medical Company, Inc.

ProTrack Microcatheter

Coiled stainless steel, PTFE, Pebax

2.9

2.9

2.9

145

0.025

Up to 0.024

Yes

No

Boston Scientific Corporation

Mamba 135 Microcatheter

Coil

2.9

2.4

1.4

135

0.018

0.014

Yes

Yes

Boston Scientific Corporation

Mamba Flex 135 Microcatheter

Coil

2.9

2.1

1.4

135

0.018

0.014

Yes

Yes

Boston Scientific Corporation

Mamba Flex 150 Microcatheter

Coil

2.9

2.1

1.4

150

0.018

0.014

Yes

Yes

Cardiovascular Systems, Inc. (manufactured by OrbusNeich)

Teleport Control Microcatheter

Stainless steel braid and coil with outer nylon Pebax jacket

2.7

–

2.1

135, 150

0.0157

0.014

Yes

Yes

Cardiovascular Systems, Inc. (manufactured by OrbusNeich)

Teleport Microcatheter

Stainless steel braid and coil with outer nylon Pebax jacket

2.6

–

2

135, 150

0.0157

0.014

Yes

Yes

Cook Medical

Cantata 2.5

Braided stainless steel, PTFE, Pebax

2.5

2.5

2.5

100, 110, 135,

150

0.021

0.018 (maximum)

Yes

Yes

Cook Medical

Cantata 2.8

Braided stainless steel, PTFE, Pebax

2.8

2.8

2.8

100, 110, 135,

150

0.025

0.021 (maximum)

Yes

Yes

Cook Medical

Cantata 2.9

Braided stainless steel, PTFE, Pebax

2.9

2.9

2.9

100, 110, 135,

150

0.027 (0.69

mm)

0.025 (maximum)

Yes

Yes

Merit Medical

SwiftNinja Steerable

Tungsten-braided shaft

2.9 (0.97

2.9 (0.97

2.4

125

0.021 (0.54

0.018

Yes, two

Yes

Systems, Inc.

Coronary Microcatheter

mm)

mm)

(0.80

mm)

mm)

markerbands

Millar, Inc.

Mikro-Cath

Nylon tube

2.3

–

3.5

120

–

Guide catheter used for delivery

No

No

Reflow Medical, Inc

Wingman14C Crossing Catheter

Braided catheter with extendable beveled tip

2.7

2.7

2.7

–

–

0.014

Yes

Yes

Teleflex

Minnie Support Catheter 0.014

Polymer

3.1

2

1.6

135, 150

–

0.014

No; three radiopaque marker bands near distal tip

Yes

Teleflex

SuperCross Microcatheter OTW - 0.014 Angled Tips: 45°, 90°, 120°, and 90°

Extended Tip

Dual coil design, platinum/tungsten coil tip

3.2

–

2.4

130, 150

0.017

0.014

Yes, platinum/tungsten coil tip

Yes

Teleflex

SuperCross Microcatheter OTW - 0.014 Straight and Flexible Tip

Braided

2.5

–

1.8

130, 150

0.017

0.014

Yes, one markerband

Yes

Teleflex

Turnpike Catheter

Hybrid multilayer: dual bidirectional coils with inner braid

2.9

2.6

1.6

135, 150

0.0165

0.014

Yes, tungsten- loaded tip

Yes

Teleflex

Turnpike Gold Catheter

Hybrid multilayer: dual bidirectional coils with inner braid and external nylon spiral coil

2.9

2.9

2.1

135

0.0165

0.014

Yes, gold-plated tip

Yes

Teleflex

Turnpike LP Catheter

Hybrid multilayer: dual bidirectional coils with inner braid

2.9

2.2

1.6

135, 150

0.0165

0.014

Yes, tungsten- loaded tip

Yes

Teleflex

Turnpike Spiral Catheter

Hybrid multilayer: dual bidirectional coils with inner braid and external nylon spiral coil

2.9

2.9

1.6

135, 150

0.0165

0.014

Yes, tungsten- loaded tip

Yes

Teleflex

Twin-Pass Dual Access Catheter

Dual-lumen catheter

3

3.5

2

135

0.017

0.014 (RX and OTW)

Yes, two markerbands

Yes

Teleflex

Twin-Pass Torque Dual Access Catheter

Dual-lumen catheter

3.5 × 3.5

2.1

135

0.017

0.014 (RX and OTW)

Yes, two markerbands

Yes

Terumo Interventional Systems

FineCross MG Micro Guide

Stainless steel braid, hydrophilic coating, tapered inner shaft, floppy distal 13- cm segment

2.6

–

1.8

130, 150

0.018

0.014

Yes

Yes

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.

Table 2

Characteristics of dual lumen microcatheters

Device

Catheter length (cm)

Distance

(RX-OTW mm)

Proximal OD (F)

Distal OD (F)

Tip OD(F)

Distal shaft shape

Inner lumen ID

GW compatibility(inch)

GC compatibility(F)

Twin pass

135

3.4/2.7

2

2

2

Oval

0.016- inch RX: 0.0165-inch OTW

0.014

≥ 5

Twin pass Torque

135

3.5

2.1

2.1

2.1

Round

0.015- inch RX: 0.0155-inch OTW distal; 0.0165-inch OTW proximal

0.014

≥ 5

Sasuke

145

3.2

2.5/3.3

1.5

1.5

Oval

0.016-inch tip and 0.017 inch shaft

0.014

≥ 5

NHancer Rx

135

2.6

2.3

1.5

1.5

Oval

0.019-inch tip and shaft

0.014

≥ 5

ReCross

140

2.6/3.4

2.3/3.3

1.5

1.5

Oval

0.019-inch tip and shaft

0.014

≥ 5

FineDuo

140

2.9

22

22

22

Round

0.017-inch tip and shaft

0.014

≥ 5

Crusade

140

2.9

22

−

−

Round

0.017-inch tip and shaft

0.014

Table 3

Steerable and angle tip microcatheters: comparison of venture wire control, supercross, and swifNINJA microcatheters (courtesy of George Kassimis et al)

Parameters

Venture wire control

SuperCross

SwifNINJA

Type of microcatheter

Steerable, Available in RX, and OTW

Fixed curve OTW

Steerable OTW

Tip of microcatheter

Deflects up to 90°*

Angled in 45°, 90° and 120°

Deflects up to 180°

Guidewire compatibility

0.014”

0.014”

0.014”

Guide catheter compatibility

6F

6F

6F

Working length in cm

145(RX), 140 (OTW)

130 and 150

125

RX segment length in cm

30

n/a

n/a

Radiopacity

8mm radiopaque tip length

Along entire angled tip

Two radiopaque markers

Hydrophilic coating length in cm

Distal 24 (RX), distal 45 (OTW)

Distal 80

Distal 80

Inner diameter

0.018” (0.46 mm)

Distal 0.017” (0.43 mm) Proximal 0.018” (0.46 mm)

0.021” (0.54 mm)

0.021” (0.54 mm)

2.2 F(0.74 mm)

2.4F (0.71 mm)

2.4F (0.80 mm)

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).

Table 4

Microcatheter failure mechanisms and clinical consequences according to Megaly's et al study

Failure method, n (%)

N = 378

Tip fracture

305(80.7%)

Due to over-torquing

141

Due to forceful pulling

81 (26.6%)

Tip was retrieved

109 (35.7%)

Tip stuck in the lesion

127 (33.6%)

Guidewire stuck in the micro catheter

39 (10.3%)

Proximal shaft and hub separation

20 (5.3%)

Shaft fracture and twisting

4 (1.1%)

Outer coil or polymer dislodgement

8 (2.1%)

Clinical consequences n (%)

Death

3 (0.8%)

Perforation

7 (1.9%)

Dissection

5 (1.3%)

Surgery

27 (7.1%)

Aborted percutaneous coronary intervention

55 (14.6%)

Periprocedural myocardial infarction

3 (0.8%)

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.