(AMERICAN COLLEGE OF CARDIOLOGY/AMERICAN HEART ASSOCIATION/AMERICAN SOCIETY OF NUCLEAR CARDIOLOGY GUIDELINES)
CAD (class I and IIa indications—evidence clearly demonstrates benefit, and evidence appears to favor benefit, respectively):
- To identify the extent, severity, and location of ischemia in patients without left bundle branch block (RBBB) or paced rhythm but who have ECG abnormalities that interfere with interpretation of exercise-induced ST-segment changes
- To assess the functional significance of intermediate coronary lesions
- To assess patients with intermediate Duke Treadmill Score
- To re-stratify risk with repeated imaging in a patient with CAD whose symptoms have changed
- To assess myocardial risk in patients with possible acute coronary syndrome with nondiagnostic ECG, initial serum markers, enzymes, and a normal resting scan
- To risk stratify after thrombolytic therapy for acute ST-segment elevation myocardial infarction (STEMI) to detect inducible ischemia and assess infarct size
- To assess location and severity of inducible ischemia after non–ST-segment elevation myocardial infarction (NSTEMI) in patients whose angina is stabilized with medical therapy
- To risk stratify patients without symptoms 3 to 5 years after revascularization (percutaneous coronary intervention [PCI] or coronary artery bypass grafting [CABG])
- For initial test in patients at high risk (diabetes, or otherwise defined as having a >20% 10-year risk of coronary event)
- For evaluation before noncardiac surgery
- Initial diagnosis of CAD in patients with intermediate pretest probability of disease and abnormal baseline ECG
- Prognostic assessment of patients with suspected or proved CAD
- Evaluation of patients after change in clinical status (e.g., acute coronary syndrome)
- Assessment of patients with intermediate clinical risk, abnormal ECG, moderate to excellent functional capacity, and high-risk surgery
- Patient refusal
- Mental or physical impairment leading to inability to safely walk on a treadmill
- STEMI (within 2 weeks); NSTEMI (within 3 days)
- High-risk unstable angina; ongoing chest pain, chest pain within the last 12 hours associated with ST elevation or new ST depression, or ongoing requirement of IV nitroglycerin infusion
- Uncontrolled arrhythmias
- Symptomatic severe aortic stenosis: aortic valve area <1.0 cm2 or peak velocity >4 m/sec
- Decompensated heart failure
- Acute pulmonary embolus or pulmonary infarction
- Acute myocarditis or pericarditis
- Acute aortic dissection
- Severe hypertension (systolic blood pressure [SBP] >180 mm Hg or diastolic blood pressure [DBP] >110 mm Hg)
- Known left main coronary stenosis.
- Electrolyte abnormalities.
- Hypertrophic cardiomyopathy and other forms of outflow tract obstructions.
- Patients are required in many scanners to lie with their arms over their head for 16 minutes while scanning—those unable to do so (because of musculoskeletal issues) cannot be scanned, and alternative imaging should be considered.
- Morbid obesity may preclude patient being able to fit into scanner, and alternative imaging should be considered.
- Treadmill, ECG machine, and monitor
- SPECT imaging camera
- Portable BP cuff and stethoscope
- Equipment for IV catheterization
- 20-gauge IV catheter
- Alcohol swab
- Local anesthetic and 3-mL syringe with small (25- or 30-gauge) needle for subcutaneous infiltration of local anesthetic
- Radiotracer doses (weight adjusted); one each for rest and stress (e.g., Tl, 99mTc)
- Crash cart with resuscitation equipment, resuscitation drugs, and defibrillator
- Oxygen source and delivery system (nasal cannula, face mask)
CORONARY ARTERY ANATOMY
- Coronary blood supply is via the RCA and the LMCA, which arise near the anterior and left aortic valvular sinuses in the proximal ascending aorta, respectively.
- The RCA passes anteriorly and to the right and enters the AV groove. It descends to the right cardiac border and then curves around posteriorly, ending in most cases just a little to the left of the junction of the interatrial and interventricular grooves (or the so-called crux of the heart). The RCA supplies the RA and RV, the posteroinferior one-third of the interventricular septum, and a variable portion of the diaphragmatic LV. In about 65% of cases, the RCA supplies the SA node (in 35% of cases, it is supplied off of a branch of the circumflex artery). In 80% of cases, the RCA provides the blood supply to the AV node.
- The LMCA supplies a larger volume of myocardium, including the LA, LV, and most of the interventricular septum. The LMCA enters the AV groove and divides into two or three main branches: the anterior interventricular artery (or LAD), the circumflex artery, and (in some cases) the left diagonal artery. In 35% of cases, the circumflex artery supplies the SA node, and in 20% of cases it supplies the AV node. In about 20% of cases, the circumflex supplies the posterior interventricular artery, and the coronary circulation is termed left dominant. The LMCA supplies most of the LV, a narrow strip of RV, the anterior two-thirds of the interventricular septum, and most of the LA.
NORMAL AND ABNORMAL SCANNING IMAGES
The principles of SPECT stress imaging rely on regional redistribution of coronary blood flow during stress.
- Normal SPECT display. Several imaging planes are used to demonstrate radiotracer uptake in the myocardium; the short-axis images, vertical long-axis images, and horizontal long-axis images.
- Abnormal SPECT display.