after the introduction of drug eluting stents when the principle is to avoid injuring segments that will not be covered by stents, a situation known as geographic miss, smaller balloons tend to be used for predilatation, just aiming to create a passage for stent insertion and exclude the presence of truly undilatable lesions [8]. Postdilatation balloons should be shorter than the stent and short balloons (8 or also 6 mm long) are recommended for effectively postdilating resistant diaphragm lesions.
The first angioplasty balloons were composed of flexible polyvinyl chloride (PVC), a material characterized by great compliance. Subsequent generations were made of cross‐linked polyethylene, polyethylene terephthalate (PET), nylon, Pebax, and polyurethane. Most modern balloons allow controlled limited expansion, burst resistance up to high pressure, and have a low crossing profile. The tip style (tapering, length, flexibility) varies substantially among different balloons, and is one of the factors contributing to a successful crossing. Compliant balloons show a linear increase in diameter with increasing inflation pressure whereas the diameter increase tends to plateau in semi‐ or non‐compliant balloons until reaching the rated burst pressure. More compliant balloons have a limited pressure range whereas non‐compliant balloons have a limited diameter range and are useful for treating resistant lesions requiring high pressure inflation or postdilatation. Semi‐compliant balloons fall between these two extremes and tend to be multipurpose “workhorse” balloons. Familiarity with the compliance charts of balloons is necessary to reduce the risk of trauma to the healthy vessel or of exceeding the vessel elasticity and induce dramatic vessel ruptures. Terms encountered on these charts include the following:
1 Nominal: the pressure at which the balloon reaches its nominal diameter (diameter on the label).
2 Rated burst pressure: the pressure below which in vitro testing has shown that 99.9% of the balloons will not burst with 95% confidence.
3 Mean burst pressure: the mathematical mean pressure at which a balloon bursts.
Wall stress within a cylindrical balloon can be represented by the following equations:
where σradial = radial stress, σaxial = axial or longitudinal stress, p = pressure, d = diameter, and t = wall thickness. It can be seen that wall stress is linearly proportional to diameter which means that higher dilatation pressure is possible with smaller diameter balloons. Furthermore, axial stress is half of radial stress which means that balloon rupture is usually longitudinal rather than circumferential and therefore less likely to result in vessel trauma.
Balloons have proximal and distal radiopaque markers to allow positioning (one central marker for some small diameter balloons). Rewrap refers to the ability of the balloon to regain its original folded state following deflation. Deflation and rewrapping can take time when large and long balloons are used. Rewrapping is essential to allow safe withdrawal of the balloon into the catheter. Stent deployment balloons tend to rewrap less well, have more variable expansion characteristics, and should ideally not be used for postdilatation.
The past decade has heralded the development of several specialty balloons including ultralow crossing profile balloons, cutting balloons, focal force balloons, and drug‐coated balloons (Figure 5.10) with specific applications for each type of balloon.
Ultralow crossing profile balloon catheters have been recently developed, aimed to improve crossability and pushability to treat the most complex lesions. As mentioned above, the “crossing profile” is one of the parameters that has to be considered when selecting a balloon, especially when facing very severe calcific lesions that may represent a challenge for the operators. In such cases, using an ultralow profile balloon, characterized by optimal tracking and crossing properties, may help to solve the problems almost in all cases. Among these, balloon catheters such Ikazuchi (Kaneka, Osaka, Japan) and Tazuna (Terumo, Tokyo, Japan) have become routinely available. The Ikazuchi Zero catheter balloon is a specialized semi‐compliant balloon which presents good crossability in CTO or calcified lesions with its very low entry‐ and balloon‐profile. Tazuna balloon catheter crossing performance is gained by low entry profile (0.40 mm/0.016”) for the most challenging lesions, a flexible and robust tip to cross tight lesions and stent struts and by the presence of a hydrophilic coating on the distal shaft able to facilitate navigation through tortuous vessels and calcified distal lesions. Moreover, the mid‐shaft construction balances flexibility and stiffness, maximizing the transmission force to the distal section enhancing the pushability of the catheters.
The Glider balloon catheter is a rapid‐exchange PTCA catheter compatible with 0.014” coronary guide wires and 6 F guiding catheters. The most distinctive feature of the Glider balloon is the presence of an oblique cut of the distal tip, which can be rotated from the proximal hub because of its unique braided reinforced and lubricious shaft. The balloon diameters currently available are 2.5 and 3.0 mm, the length is 4.0 mm with a single mid marker and a rated burst pressure of 16 Atm with low compliance. This short balloon is specifically designed for optimal side branch ostium expansion without damaging the distal side branch, and thus, minimizing the risk of side branch dissection [19].
A list of the most commonly used ultra low profile PTCA balloon is reported in Table 5.6.
Table 5.6 List of commonly used ultra low profile PTCA balloon.
| Lesion Crossing profile(“) /balloon diameter (mm) | |
|---|---|
| Nic Nano Hydro CTO Balloon, SIS medical, Swiss | 0.0195” / 0.85mm |
| Tazuna, Terumo, Tokyo, Japan | Not reported / 1.25mm |
| Ikazuchi (Kaneka, Osaka, Japan | 0.0157” / 1mm |
| Sapphire II Pro CTO, Orbus Neich, Hong Kong | 0.016” / 1mm |
Cutting balloon and scoring balloon catheters represent two different strategies developed in the context of resistant lesion preparation, enabling to prepare the coronary plaque and to create cracks in the calcium or dense fibrotic wall before stenting.
The cutting balloon has been available for almost 30 years. It is a semi‐compliant balloon with three thin sharp blades mounted on its body, designed to cut the continuity of fibrocalcific plaque once the pressure of the balloon forces them against the vessel wall, creating fissures on the plaque. The Flextome cutting balloon (Boston Scientific, Malborough, MA, USA), has three blades equally spaced around its circumference which come into contact with the arterial wall and score the vessel wall. The balloon is specifically indicated for discrete lesions with resistance to conventional balloon angioplasty without heavy calcification. Despite its theoretical advantages, in the Cutting Balloon Global Randomized Trial the primary endpoint of six‐month binary restenosis did not differ between CBA and POBA (31% vs. 30%, p=0.75) and the rate of perforation was higher with CBA (0.8% vs. 0%, p=0.03) [20]. These negative results, together with the difficulties associated with cutting balloon delivery due to its high crossing profile (0.041‐0.046”), led to the development of the newer generation of cutting balloon Wolverine™ Cutting Balloon (Boston Scientific, USA). In the Wolverine CBA, the atherotome’s support thickness has been reduced, becoming compatible with 6 Fr catheters for all diameters, without affecting the functional height of the blade, resulting in an overall smaller crossing profile and improved crossability.
Scoring balloons, also known as “focal force balloons”, are semicompliant balloons encircled by scoring elements.
