Diagnostic Evaluation: Imaging, Electrocardiography, and Cardiac Catheterization
Imaging
Transthoracic echocardiography is first-line for anatomy, shunts, valves, and ventricular function. Cardiac magnetic resonance is the reference standard for right ventricular volumes and function, regurgitant fractions, and flow quantification - essential in tetralogy of Fallot, conduits, and aorta surveillance. Cardiac CT excels for coronaries, stents, conduit calcification, and when MRI is contraindicated. Always pair imaging with four-limb blood pressures and pulse oximetry.
Electrocardiography
The ECG encodes anatomy and prior surgery. Right bundle branch block is expected after tetralogy repair; a QRS of 180 ms or more flags risk and prompts consideration of pulmonary valve replacement. Complete heart block occurs at roughly 1–2% per year in congenitally corrected transposition. Fontan patients commonly have sinus node dysfunction or intra-atrial reentrant tachycardia, which may be the first clue to pathway obstruction.
Catheterization
Right and left heart catheterization quantifies pressures, shunts, and reactivity; it tests pulmonary vasoreactivity before considering repair or pregnancy. Qp/Qs is derived from oxygen saturations via the Fick principle. Coronary anatomy and anomalous courses require angiography or CT before surgery.
Traps
Assuming normal oxygen saturation excludes a shunt; a step-up in the right heart may be small. Misreading post-surgical RBBB as ischemia. Forgetting that a normal echocardiogram cannot exclude aortopathy or coronary anomalies in adults. Do not compute Qp/Qs from assumed rather than measured saturations.
Rule of thumb
In ACHD, one image is never enough - combine echo with CMR or CT for any right heart, conduit, or aortic question.