(b) Kilovoltage, mAs. As compared to the kVp values for routine
radiography of the chest of similar size and for comparable radiographs, an increase of
about 15 percent is necessary for angiocardiograpy. When a grid is used, a tube
tension of about 100 kVp is a sound starting value. The mAs values should be adjusted
so as to obtain the desired density and contrast of the opacified structures, more or less
disregarding the pneumatized lung fields. Whenever there is an element of doubt, it is
better to favor overexposure than to risk underexposure.
(c) SID. An SID of 40 inches is generally used with interventional
C-arms, but can be slightly greater with larger units.
3-22. CARDIAC CATHETERIZATION
a. Patient Preparation and Administration of Sensitivity Test. This has
been covered earlier in the section. Figure 3-11 demonstrates a cardiac catheterization
with the injection of contrast during diastole and systole.
b. Preliminary Procedure.
(1) A combination radiographic-fluoroscopic unit (and television, if available)
is put in operative order by the specialist. The table unit is adjusted in the horizontal
position and, when indicated, a soft synthetic rubber mattress is placed on the tabletop
to ensure the comfort of the patient.
(2) When the patient arrives at the x-ray clinic, he is placed on the x-ray
table in the supine position and sterile draped.
A cardiac catheterization layout is prepared.
(4) The site of insertion (for example, antecubital fossa) is made aseptic,
local anesthesia is administered, and a selected vein is surgically exposed. A size 8 or
9 French ureteral-type catheter, 100 to 125 cm long, connected to a regular saline
infusion set by a stopcock complex and adjusted for continuous saline perfusion, is
inserted into the vein through the surgically induced opening. The fluoroscopic
apparatus and spot-film assembly are moved into position over the patient's chest,
adjusted to the required height, and locked in place. The specialist should make certain
that the self-recording time clock is in the catheter in the heart, fluoroscopic circuit and
is set to accurately tally the total exposure.
c. Fluoroscopic and Spot-Film Procedure. The examiner advances the
catheter into the initial position in the heart under fluoroscopic control. Samples of
blood are aspirated into a syringe connected to the stopcock complex and transferred
into special containers for laboratory analysis. Usually, spot films are exposed to record
the catheter in the various positions. The spot films are numbered to correspond to the
numbered samples of blood.