There are two kinds of invasive procedures that are used in the practice of pediatric cardiology. The first is cardiac catheterization and angiocardiography, which together are used for diagnosis (diagnostic catheterization). The second is to treat certain structural heart defects nonsurgically using specially designed catheters and implantable devices that are delivered through cardiac catheters (therapeutic cardiac catheterization).
Cardiac Catheterization and Angiocardiography
Cardiac catheterization and angiocardiography usually constitute the final definitive diagnostic tests for most cardiac patients. They are carried out under general sedation using various sedatives (discussed later). For newborns, cyanotic infants, and hemodynamically unstable children, general anesthesia with intubation may be used.
Under local anesthesia and with strict aseptic preparation of the skin, catheters are placed in peripheral (most commonly the femoral) vessels and advanced to the heart and central vessels under fluoroscopy with image intensification to reduce radiation exposure. At each position in the heart and blood vessels, values of pressure and oxygen saturation of blood are obtained. The oxygen saturation data provide information on the site and magnitude of the left-to-right or right-to-left shunt, if any. The pressure data provide information on the site and severity of obstruction. Cardiac output may be obtained from oxygen saturation data (e.g., the Fick principle) or by indicator dilution (e.g., indocyanine green dye) or thermodilution (e.g., cold saline injection) technique. Selective angiocardiography is usually performed as part of the catheterization procedure (described later).
Normal Hemodynamic Values
Normal oxygen saturation on the right side of the heart is usually 70% but it may vary between 65% and 80%, depending on cardiac output. Left-sided saturations are usually 95% to 98% in room air. In newborns and heavily sedated children, the oxygen saturation may be lower. Pressures are lower in the right side than in the left side of the heart, with systolic pressures in the right ventricle (RV) and pulmonary artery (PA) about 20% to 30% of those in the left side of the heart ( Fig. 7-1 ).
Routine Hemodynamic Calculations
The following calculations are routinely obtained: flow and resistance for systemic and pulmonary circuits and left-to-right or right-to-left shunt.
Flows (Cardiac Output) and Shunts. Flow is calculated by use of the Fick formula:
Pulmonary flow ( Q ˙ p ) = Vo 2 C PV − C PA
Systemic flow ( Q ˙ s ) = Vo 2 C AO − C MV
Oxygen consumption is either directly measured during the procedure or estimated from a table for children 3 years and older (see Appendix A , Table A-6). Assumed oxygen consumption of 150 to 160 mL/min/m 2 is used in older infants and children. In infants under 2 to 3 weeks of age, 120-130 mL/min/m 2 may be used. Oxygen capacity is the maximum quantity of oxygen that can be bound to each gram of hemoglobin (i.e., 1.36 mL × Hb level; each gram of hemoglobin [Hb] combines maximally with 1.36 mL of oxygen). Oxygen saturation is the amount of oxygen bound to hemoglobin compared with the oxygen capacity, and it is expressed as a percentage.
When there is a pure left-to-right or right-to-left shunt, the magnitude of the shunt is calculated as follows:
Left – to – right shunt = Q ˙ p − Q ˙ s
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
