Balloons can be divided in categories according to the maximal pressure they can sustain: low-pressure, medium-pressure, high-pressure and ultra-high-pressure balloons. The limit between the medium- and high-pressure balloons is not well defined, and for this reason, they are here described in the same group. Table 7.1 summarizes some of the characteristics of currently available balloons.

Low-pressure balloons are characterized by their high compliance with low nominal and burst pressure rates (less than 10 atm). They come in various lengths and diameters and usually have small profiles and flexible shafts. They are very useful for balloon dilation of pulmonary and aortic valves in neonates, infants and children and may be used for dilation of aortic coarctation or vein stenosis in the young child. The low pressure they sustain and their high compliance make them unsuitable for dilation of ‘pressure-resistant’ stenosis in pulmonary arteries and for stent placement. When low-pressure dilation fails to open sustainably a stenosis, the analysis of how the balloon behaves during inflation and deflation with the low-pressure balloon remains very useful to understand the lesion. It will be possible to differentiate a long segment stenosis from a localized stenosis or a pressure-resistant lesion from a compliant lesion that recoils after balloon deflation. This will guide subsequent intervention. Low-pressure balloons are most of the time hand inflated by the operators. The use of an indeflator remains however recommended to avoid balloon rupture.

The second category includes the medium- and high-pressure balloons with burst pressure rates between 10 and 20 atm for most of them. The shaft is often stiffer and the profile higher than for the balloon catheters of the first category. They are very useful for pressure-resistant lesions (not responding to the ‘low-pressure’ balloons) especially in pulmonary arteries or calcified conduits and are indicated for stent insertion. They must be inflated with an indeflator to control the inflation pressure. A large panel of balloons is currently available in this category (Table 7.1).

The ultra-high-pressure balloons are more recent in the paediatric cardiology field. They are completely noncompliant balloons, made of ultra high molecular weight polyethylene (UHMWPE). This very resistant fabric supports very high pressures, often up to 30 atm or more. They are useful for treating in-stent stenosis or stenosis adjacent to stents, often by rupturing the previously inserted restrictive stent. They may also be helpful to rupture stent cells when stents cover side branches or to dilate very resistant non-stent-related stenosis. Some of those balloons, originally for vascular use, have particularly long shoulders, and this has to be taken into account when choosing the appropriate balloon length, especially in small children. The ultra-high-pressure balloons need to be inflated with special ‘high-pressure’ indeflators.