Tips and Pitfalls -- Balloon Catheter

I. BALLOON CATHETER SELECTION AND BALLOON SIZING (Table)

Selection of an appropriate-sized balloon catheter for the stepwise dilatation technique is extremely important in order to avoid creating severe mitral regurgitation during PTMC. Our balloon catheter selection methods have evolved from continuing efforts to minimize this complication [1, 2].

Current selection guidelines are based on balloon reference size derived from patient height, transthoracic echocardiographic findings of the mitral valve, and fluoroscopic presence of valvular calcification. The reference size (RS) is calculated according to the simple formula previously described [1, 3]: patient height (in cm) is rounded to the nearest zero and divided by 10, and 10 is added to the ratio to yield the RS (in mm); e.g., if height = 147 cm, then RS = 150/10 + 10 = 25 mm.

TABLE: Catheter Selection and Balloon-Sizing Based on Patient Height
and Valvular Status

REFERENCE SIZE (RS) (mm)

Height (cm) (rounded to nearest 0) x 1/10 plus 10
e.g. height = 147 cm
RS = 150 x 1/10 + 10 = 25 mm

CATHETER SELECTION

Valvular Status

Balloon Catheter

Pliable	RS matched (e.g. PTMC-26 for RS = 25 mm)
Calcified/SL	One-size < RS matched (e.g. PTMC-24 for RS = 25 mm)

BALLOON SIZING

Valvular Status

Initial Increments

Pliable	(RS - 2) mm	1 mm, or 0.5 mm in high pressure zone** (if MR or unilateral commissural split)
Calcified/SL	(RS - 4) mm	1 mm (low pressure zone) 0.5 mm (high pressure zone*)

MR = mitral regurgitation, preexisting or increased; RS = reference size; RS matched = catheter with its nominal balloon size = RS; SL = severe subvalvular lesions; Low pressure zone* = balloon diameter < 2 mm of nominal balloon size. High pressure zone** = balloon diameter within 2 mm of nominal balloon size. (Refer to pressure-volume relationship in "Controlled Stepwise Dilatations" under PTMC Procedures.)

In patients with pliable, noncalcified valves, as determined by echocardiography, a catheter with a nominal balloon size at least that of the RS (an RS-matched catheter) is used. In contrast, because of the persuasive correlation between severe subvalvular disease as detected by transthoracic echocardiography [2-5], fluoroscopically visible valvular calcification [2] and significant mitral regurgitation during PTMC, in patients with such morphologic risk factors, a balloon catheter one size smaller than an RS-match is selected. Therefore, in the above example with an RS of 25 mm, a PTMC-26 catheter would be selected for a pliable, noncalcified valve, and a PTMC-24 catheter for a calcified valve and/or a valve with severe subvalvular disease.

References:

Lau KW, Hung JS: A simple balloon-sizing method in Inoue-balloon percutaneous transvenous mitral commissurotomy. Cathet Cardiovasc Diagn 1994;33:120-129.
Lau KW, Hung JS: "Balloon impasse" - A marker for severe mitral subvalvular disease and a predictor of mitral regurgitation in Inoue-balloon percutaneous transvenous mitral commissurotomy. Cathet Cardiovasc Diagn 1995;35:310-319.
Hung JS, Chern MS, Wu JJ, Fu M, Yeh KH, Wu YC, Cherng WJ, Chua S, Lee CB: Short- and long-term results of catheter balloon percutaneous transvenous mitral commissurotomy. Am J Cardiol 1991;67:854-862.
Hernandez R, Macaya C, Bañuelos C, Alfonso F, Goicolea J, Iñiguez A, Fernandez-Ortiz A, Castillo J, Aragoncillo P, Aguado MG, Zarco P: Predictors, mechanisms and outcome of severe mitral regurgitation complicating percutaneous mitral valvotomy with the Inoue balloon. Am J Cardiol 1992;70:1169-1174.
Chen C, Wang X, Wang Y, Lan Y: Value of two-dimensional echocardiography in selecting patients and balloon sizes for percutaneous balloon mitral valvuloplasty. J Am Coll Cardiol 1989;14:1651-1658.

II. BALLOON PRETESTING FOR BALLOON-SYRINGE MISMATCH (Figure 6)

Balloon-size Pretesting

Although the volume predefined by red marks on the syringe and its corresponding balloon size at full inflation have been tested by the manufacturer, balloon-syringe mismatch may occur. While this mismatch is usually mild, gross mismatch may take place when the catheter and the syringe are from different packagings. The mismatch, if undetected, may result in either underinflation or overinflation of the balloon. The former may result in suboptimal valvular dilatation, and the latter, in severe mitral regurgitation.

Figure 6
Balloon Pre-testing

Click to View Larger Image

Therefore, before inserting the balloon catheter into each patient, the balloon diameters should be confirmed using a two-step test. First, the syringe should be filled with diluted contrast to the mark corresponding to the balloon diameter chosen for the first inflation (Figure 6, upper panel) (see BALLOON SIZING, above). The balloon should then be fully inflated, and its diameter measured with a caliper which is provided with the catheter set. If there is a mismatch, the difference should be noted and adjusted during the second step of testing when the balloon is inflated to its nominal diameter (Figure 6, lower panel).

Disconnect syringe after pretesting

After the pretesting exercise, the syringe is disconnected from the balloon catheter for two reasons:

to purge the syringe of any remaining air, and
to avoid inadvertent balloon overinflation at its nominal size during first time dilatation of the mitral valve.

After the catheter has been inserted into the left atrium, the air-free syringe filled with diluted contrast corresponding to the predetermined initial balloon diameter is reconnected to the catheter.

III. BENT BALLOON CATHETER TIP (Figure 7)

Kinking of the balloon occurs if the inner tube is inadvertently pushed forwards when the balloon segment is unsupported by a metal tube, guide wire or stylet during in vitro [outside the body] preparation of balloon catheter.

Figure 7
Kinked Balloon

Click to View Larger Image

The kinking may also take place during placement of the catheter in the left atrium if the guide wire is withdrawn before releasing the inner tube from its locked position (Figure 7, A). Once the tip is bent, subsequent attempts at crossing the mitral valve with the catheter may be extremely difficult, if not impossible. In addition, it may be impossible to reinsert the guide wire to retrieve the balloon catheter from the left atrium.

This problem may be overcome by 1) pulling the inner tube to its limit to shorten the balloon segment, 2) carefully inflating the entire balloon in the left atrium in an attempt to straighten the kinked inner tube in the balloon segment, 3) passing the guide wire through the deflated balloon to further straighten the balloon segment, and 4) inserting the metal tube over the guide wire and advancing it to its locked position along with the inner tube (Figure 7, B). Following the above procedures, the balloon segment remains fully straightened, even if the guide wire is removed (Figure 7, C). To continue the balloon dilatation procedure, the inner tube is unlocked and pulled back with the metal tube, and then the guide wire is removed together with the metal tube.

* Coming Soon