Radionuclide Ventriculography

Anatomy and Physiology

The RNV scan can help examine the anatomy and physiology related to each cardiac cycle. The radionuclide tracer is based on a principle that the amount of radioactivity in each chamber is proportional to the amount of volume in that chamber.[5] The volume of each ventricle at the end of systole is called end-systolic volume (ESV), and at the end of diastole is called end-diastolic volume (EDV). The difference between EDV and ESV represents stroke volume (normal range 80 to 100 ml). While the ejection fraction (EF) is the percentage of the EDV ejected by the ventricle during systole, cardiac output is the product of the stroke volume and the heart rate (HR).

The wall motion can be assessed through the RNV scan and classified as normal wall motion, hypokinetic (decreased wall motion), akinetic (no wall motion), or dyskinetic (paradoxical wall motion). The heart muscle receives its vascular supply through the coronary arteries; the left anterior descending coronary artery supplies the anterior wall, intraventricular septum, apex, and a part of the anterolateral wall of the left ventricle; the left circumflex artery supplies the left atrium, posterolateral wall and a part of the anterolateral wall; and the right coronary artery supplies right ventricle, right atrium and the posterior portion of the intraventricular septum. By delineating the segmental wall motion abnormalities seen with ischemia or infarction, the radionuclide ventriculography can help localize the corresponding coronary artery supplying to the myocardium.

Indications

Indications of radionuclide ventriculography include: 

• Assessment of the left/right ventricular systolic function in a patient with coronary artery disease (CAD), valvular heart disease, atrial arrhythmia, congenital heart disease, myocardial disease, or before starting cardiotoxic chemotherapy.
• Assessment of left ventricular diastolic function in patients with congestive heart failure (CHF) with preserved EF
• Serial monitoring of the left ventricular function while on cardiotoxic chemotherapy
• Regional wall motion assessment in a patient with the low-intermediate probability of CAD when myocardial stress perfusion imaging (MPI) is not available. 
• Assessment of the ventricular synchronicity prior to CRT placement

Contraindications

• In pregnant or nursing patients to avoid radiation exposure to the fetus or baby
• History of an allergic reaction to the radioactive tracer

Equipment

• Electrocardiogram machine
• Blood pressure machine
• A radioactive tracer (TI-201 or Tc-99m-labelled)
• Gamma camera
• Treadmill or stationary bicycle for exercise scan 
• Computer system with software for final data processing and analysis

Personnel

The RNV scan should be performed by a qualified nuclear medicine technologist to obtain and process images under the supervision of a cardiologist, radiologist, or nuclear medicine physician.  

Preparation

The rest RNV scan does not require any specific preparation.

The exercise RNV scan would require 4 to 6 hours of fasting. Additionally, the patient should avoid caffeinated drinks 12 hours before the procedure and should wear comfortable clothes/shoes. 

Technique or Treatment

The patient is positioned comfortably on the exam table, EKG (electrocardiogram) leads are attached to the chest wall, and a blood pressure cuff is wrapped around the arm. Baseline heart rate, EKG, and blood pressure are recorded before starting the test and then monitored closely during the entire exam.

The scan requires the tagging of the patient's red blood cell (RBC) with the radiotracer (99m-technetium), which could be done in vivo or in vitro and then injecting it (around 20 mCi as per patient's weight) through an intravenous line. After that, the study can proceed using one of three different methods, including first-pass study, gated equilibrium ventriculography, or gated SPECT image acquisition. The EKG gating is done by dividing the cardiac cycle into 16 or 32 frames and using R wave as a trigger to obtain proper sampling. One prerequisite for the EKG gating is less than 10% of premature ventricular contraction at baseline. A variation in the heart rate or rhythm, such as sinus arrhythmia, results in distortion of the data. The exercise scan can be done with a stationary bicycle or a pharmacological agent (dobutamine). 

In the first pass study, the gamma camera acquires the imaging of the heart, lung, and great vessels in a rapid sequence during the initial rapid transit of the radioactive bolus with a 30-degree RAO projection. 

In a gated equilibrium radionuclide ventriculography, images are taken after the radiotracer achieves a state of equilibrium. It acquires images in three different views, including an anterior view, a left oblique view (at 45 degrees) to visualize the septum, and a left lateral oblique view.  While during exercise, only the left anterior oblique view is obtained at different stages of exercise. 

In a gated SPECT acquisition, the structure of interest can be isolated precisely to assess the ventricular segment contractility accurately. It creates long axis, short axis, and three-dimensional volumetric images. The ejection fraction assessed with the SPECT images is more accurate than the planar method due to atrial interference in the planar method, which would underestimate the ejection fraction. 

Qualitative and Quantitative Assessment 

To analyze the data qualitatively and quantitatively, different images, including functional, stroke volume, paradox, and amplitude images, are obtained. In the qualitative assessment, the cinematic display on the screen allows the visual evaluation of the ventricular contractility and wall motion abnormality. While in the quantitative analysis, the computer counts the change in radioactivity in the region of interest (ROI) during a cardiac cycle, which is proportional to the change in the blood volume in that area.  From this, the time-activity curve can be generated to obtain the end-systolic and end-diastolic volume.  The accuracy of calculation depends on the precise selection of the region of interest. Additionally, the regional ejection fraction and contractility undergo an assessment by dividing the ventricle into segments.

Complications

The RNV scan is a safe procedure without serious adverse reaction as the scan uses a small dose of the radiotracer, and it gets cleared through the kidney within 24 hours. The radiation exposure from RNV is equivalent to that of a computerized tomography scan (CT scan).

The dobutamine used during the exercise scan could give little nausea, headache, palpitation, or chest discomfort, which usually wears off in a few minutes.

Clinical Significance

The RNV scan is a gold-standard test to assess the left ventricle function before and during the cardiotoxic chemotherapy treatment. Additionally, it has shown itself to be a cost-effective test for ventricular function monitoring during cardiotoxic chemotherapy.[6] The previous study has reported its usefulness in assessing perioperative cardiac risk and mortality.[7] 

The regional wall motion abnormality reported on scan could signal towards coronary ischemia or infarction. Additionally, it can provide prognostic information for coronary artery disease and an acute coronary event.[8][9] Furthermore, it can aid in the differential diagnosis of dilated, hypertrophic, or restrictive cardiomyopathies. The ventricular synchrony assessed by the radionuclide ventriculography can be helpful prior to CRT as the echocardiographic parameters have not shown the consistency in predicting the cardiac outcome.[3][10]

Enhancing Healthcare Team Outcomes

The primary care provider can use the RNV scan to assess the left ventricular function for any new sign or symptom of CHF, particularly for the patient taking cardiotoxic chemotherapy. The test can be performed in 1 to 2 hours, with results obtained immediately. The patient care should be in coordination with cardiology and oncologist for any drop in ventricular function to adjust the chemotherapy regimen. 

Nursing, Allied Health, and Interprofessional Team Interventions

The team coordinator should call the patient to confirm the date, time, and location of the procedure. The nursing staff can call the patient a few days prior to the appointment to brief about test day preparation and expectations. 

On a test day, the technician should monitor the time and protocol. Additionally, the technician should instruct the patient appropriately to lessen the motion and obtain accurate images. 

Nursing, Allied Health, and Interprofessional Team Monitoring

The patient should receive diligent monitoring closely during the test with the EKG machine. The nursing staff should observe the patient for any allergic reaction to the radioactive tracer and should notify the supervising physician immediately for any allergic reaction.

The patient should be monitored with serial blood pressure reading and continuous ECG rhythm during exercise scan. The facility should be equipped with an emergency response system for a pharmacological exercise scan.