Cardiac Perfusion Imaging…continued

PURPOSE

• To evaluate regional myocardial perfusion during resting and under stress • To identify and localize areas of reversible ischemia or previous infarction in patients with chest pain, suspected of having coronary artery disease, previous coronary intervention, or previous abnormal ECG examination.

Example of an Infarct = fixed defect – apparent on Stress and Rest

Protocols

• Technetium agents – 2-day stress-rest 1-day rest-stress 1-day stress-rest

Protocols

• Thallium-201 – Stress and delay • Dual isotope – Thallium rest and Technetium stress performed on the same day

Mechanism of cellular labeling

•

Sestamibi

and

Myoview

transport involves passive diffusion across the plasma and

mitochondrial

membranes •

Thallium

201 behaves physiologically as a potassium analog. Uptake reflects perfusion and sodium-potassium pump activity.( Na-K pump )

Stressing

• Physical – Treadmill or Bicycle • Pharmacologic – Adenosine – vasodilator – Dipyridamole (persantine) – vasodilator – Dobutamine – inotropic agent

Treadmill or Bicycle

PHYSICAL

Exercise stress Absolute contraindications

• High risk unstable angina. • Inadequately controlled congestive heart failure. • Uncontrolled hypertension (blood pressure >200/110 mm of Hg). • Uncontrolled cardiac arrhythmias • Severe symptomatic aortic stenosis

Exercise stress Absolute contraindications

• Acute pulmonary embolism • Acute myocarditis or pericarditis • Acute aortic dissection • Severe pulmonary hypertension • Acute myocardial infarction (<4 days)

Indications for Early Termination of Exercise

• Chest pain • Breathing difficulty • Fatigue.

• Dizziness • Signs of poor perfusion (cyanosis and pallor).

• Patient’s request to terminate the test.

Exercise stress

patients who cannot exercise adequately should undergo pharmacologic stress testing

Pharmacologic – cardiology presence

Adenosine Dipyridamole (persantine) Dobutamine

STRESS PROCEDURE

Pharmacologic stress Procedure

Cardiology Fellows and ARNP are responsible for administration of pharmacologic agents.

Dipyridamole (Persantine) or adenosine stress testing Absolute contraindications

• Asthmatic patients with ongoing wheezing • Severe COPD • Severe A-V block • Use of dipyridamole-containing medications • Caffeine within the last 12 hours • Low blood pressure • Unstable acute myocardial infarction

Indications for Early termination of Dipyridamole (Persantine) or adenosine infusion

• Severe hypotension (systolic blood pressure _80 mm Hg).

• Development of symptomatic, persistent second degree or complete heart block.

• Wheezing.

• Severe chest pain associated with ST depression of 2 mm or greater.

• Signs of poor perfusion (pallor, cyanosis, cold skin).

• Technical problems with the monitoring equipment.

• Patient’s request to stop.

Dobutamine

should not be used under the following circumstances

• Recent (<1 week) myocardial infarction. • Unstable angina. • Significant left ventricular (LV) outflow tract obstruction. • Severe aortic stenosis. • Atrial tachyarrhythmias • History of ventricular tachycardia. • Uncontrolled hypertension • Aortic dissection or large aortic aneurysm

The indications for early termination of dobutamine

are similar to those for exercise stress. Termination for ventricular tachycardia or ST-segment depression is more likely with dobutamine than with other stressors.

Nuclear

PROTOCOL

Patient preparation for Stress Studies

• Fast for 4 hours prior to the test • Avoid shunting of blood to the stomach • Precaution against vomiting during stress • If Pharmacologic stressing • No caffeine for 24 hours prior to the test

Day of test

• Identify the patient • Explain the procedure and possible side effects of the pharmacologic stress agent • Assess for pregnancy and breastfeeding • Obtain a signed consent form.

• Start an I. V.

• Administer the resting dose • Image according to protocol

Imaging

• Place patient supine on the imaging table – secure using the imaging pad straps – Make patient as comfortable as possible in order to minimize movement • Place patient’s arms overhead – use an arm support accessory if possible for support • Explain the need to breath normally, and the importance of not moving during the scan • Follow the acquisition protocol

DOSAGE

Technetium 99m Cardiolite® (Sestamibi) or Myoview™ (Tetrofosmin) Rest: 7-10 mCi Stress: 21-30 mCi Thallium-201 Stress: 2 to 3 mCi

STRESS PROCEDURE

Physical Exercise Procedure

• The patient will be attached to a 12-lead ECG, and have an IV in place. • The patient will go through a series of graded levels of exercise lasting 3 minutes each (Bruce protocol, Modified Bruce protocol).

• Record blood pressure, heart rate, and ECG every 1 minute. • The radiotracer should be injected at target heart rate and peak exercise 1 to 2 minutes prior to the conclusion of exercise.

• Record radiotracer injection time.

• The end point will be determined either by the patient’s inability to continue or at the direction of the attending cardiologist supervising the study.

• Patients are assessed for stability before discharge

STRESS PROCEDURE

Pharmacologic stress Procedure

Precautions/Restrictions: Cardiology Fellows and ARNP – are responsible for administration of pharmacologic agents.

PERSANTINE PROTOCOL

• Dose of persantine is 0.142 mg/kg/minute infused over 4 minutes.

• Maximum dose is 60 mg • Patient should be told that mild chest discomfort, flushing, headache, nausea may be encountered.

PERSANTINE PROTOCOL

• Make sure IV aminophylline is available • Start a heparin lock or use existing one. • Draw the desired Persantine dose in a 30 cc Terumo syringe. Add Normal Saline to the same Terumo syringe to a total volume of 23 cc. • Insert the filled syringed into the Baxa Rapid Rate Infuser, attach the tip of the syringe to heparin lock. To start infusion, select Rate 1, slide the ON/OFF switch to ON.

PERSANTINE PROTOCOL

• Monitor blood pressure, heart rate, and ECG every minute.

• Inject nuclear agent three (3) minutes post persantine infusion.

• If patient develops severe side-effects or severe chest pain, the effects of persantine can be reversed with IV aminophylline. – If possible, inject nuclear agent and wait 1 minute before reversing the adverse effects of persantine. – Dose of aminophylline is 125 to 250 mg IV injected at a rate of 50 mg per minute.

ADENOSCAN INFUSION PROTOCOL

• In most cases, discontinuation of the adenosine infusion is followed by a prompt (< 1 minute) resolution or improvement of the adverse effect. In rare cases, aminophylline may be required, 50 to 125 mg IV .

DOBUTAMINE PROTOCOL

• Start IV line with angiocath gauge 22 or larger.

• Mixed dobutamine 50 mg (4cc of Dobutamine 250mg/20 ml) in 96 cc of Normal Saline to make a total volume of 100 cc. prime the IV tubing and use an IVAC pump to regulate infusion based on the patients weight in kilogram (kg).

• Make sure intravenous metoprolol is available.

• Inform patient of possible side effects: chest discomfort/pain, palpitations, ect.

DOBUTAMINE PROTOCOL

• • Dobutamine is infused intravenously starting at 10 mcg/kg/min. and if tolerated, is increased every 3 minutes thereafter by 10 mcg/kg/min until a maximal dose of 40 mcg/kg/min. Target heart rate is 85% of the age-predicated maximal value. • Up to 1 mg of intravenous atropine may be given if an adequate heart rate is not achieved. • EKG, blood pressure, and heart are monitored during each stage.

T

he radioisotope is injected at peak dobutamine dose. Dobutamine infusion is continued for 1 minute after injection.

• If the effects of dobutamine need immediate reversal (eg, symptomatic tachycardia), give metoprolol 5 mg IV, may repeat every 5 minutes three times (total of 15 mg)

Myocardial Viability

• myocardial tissue that retains at least the minimal requirements for cell survival.

– cell membrane integrity – mitochondrial activity, and other metabolic functions.

Myocardial Viability

• These requirements for cell survival do not necessarily imply that the tissue is fully functional however. – viable cardiac tissue may exhibit poor to no contractile capability. • If its impairment results from reduced blood flow, it has the potential for recovery and for improved function following revascularization.

Myocardial Viability

• “

Stunned myocardium

“ – viable tissue that recovers function spontaneously following a temporary severe reduction in blood flow.

• "

Hibernating myocardium

" – viable tissue in a region of chronic coronary artery disease, whose contractile function only improves following restoration of blood flow to the myocardium.

– it is thought that hibernating myocardium is the result of chronic repetitive "stunning"

Myocardial Viability

• The standard protocol for demonstrating viability consists of a rest injection of Thallium-201 chloride, followed by 15 min, 4 hour, and 24 hour views.

• An alternative protocol employs an initial injection during stress (exercise or pharmacological), followed by imaging at 15 min, 4 hours, with re-injection and imaging at 20 min, and if needed, additional imaging up to 24 hours later.

Myocardial Viability test rationale

• There is a steady exchange of Tl-201 between the myocardial cells and the blood.

• Within 15 minutes after injection redistribution begins.

• Tl-201 will washout more quickly from normal cells than from abnormal cells. The overall effect will be a steady relative decrease in uptake in normal tissue and increase in uptake in abnormal tissue over several hours.

Myocardial Viability test rationale

• Hibernating tissue is identified as tissue that demonstrates reduced uptake immediately following initial injection, when compared to normal myocardium, but which on delayed images demonstrates normalization or "filling in".

Technique: Tl-201 for viability

•

Dose: 4.0mCi of 201Tl-chloride I.V.

•

Rest-redistribution

Inject at rest and begin imaging as soon as possible, re image at 4 and if necessary at 24 hours

•

Stress-rest-reinjection

– – – – –

Inject at peak exercise and continue exercising for at least one minute after injection Begin imaging 15 minutes after injection delayed images at 4 hours.

Re-inject 1.0-1.5 mCi and re-image at approximately 15 minutes after injection; later delayed imaging is optional

.

Imaging

•

Acquisition parameters (one or two headed cameras):

–

acquire 32-64 frames,

–

20-45 sec/frame over a 180 o to 45 o LPO.

arc from 45 o

– – –

64x64 acquisition matrix LEHR collimator Processing: varies by the camera manufacturer

–

Zoom as needed RAO

SPECT processing

• View ‘rotogram’ for patient motion. Correct if necessary • Transaxial reconstruction • Reorientation of image axis • Oblique reconstruction – apply proper filtering • Final report presentation

Gated perfusion imaging

PET 18Fluorine-FDG (2-fluoro-2-deoxyglucose)

• 18F-FDG is transported across cell membranes where it is phosphorylated to 18F-FDG-6-phosphate, and is then trapped within the viable myocardial cells, accumulating slowly.

• Viability Testing Rationale – The myocardium in a normally perfused state is largely dependent on fatty-acid metabolism. – Fatty acid metabolism in myocytes is very sensitive to reduced perfusion and hypoxia, however. • As a result, ischemic cells switch their metabolism from beta oxidation of fatty acids toward anaerobic glucose metabolism. • The energy generated from anaerobic glucose metabolism may not be sufficient to maintain contractile function, but still may suffice for the preservation of cell membrane integrity and gradients. • Hypoperfused but viable tissue is defined as normal or increased regional cardiac FDG uptake in a region of reduced uptake of a flow tracer (using 99mTc-sestamibi, 99mTc-tetrofosmin, Rb-82, or N-13 ammonia).

• Infarcted tissue will demonstrate reduced uptake of both a flow tracer and FDG (i.e. a matched defect of perfusion and metabolism).