Key points
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RNA is a time-honored method for assessment of LVEF and RVEF.
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RNA-derived EF is based on count changes and not on geometric assumptions.
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RNA can be performed with first-pass and gated equilibrium methods.
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Gated RNA can be performed with either a planar technique or tomography.
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RNA can be performed at rest, with exercise, and many other interventions.
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RNA can be performed in patients with sinus rhythm, as well as those with atrial fibrillation.
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Planar RNA can be done in any projection, but gated planar RNA uses the septal LAO projection for EF measurements.
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RNA can provide information on wall motion, LV/RV size, pulmonary transit time, diastolic function, pulmonary blood volume, intracardiac shunts, and regurgitant volume.
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Gated RNA can be used to assess dyssynchrony.
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Alternative RNA methods using different hardware and tracers as well as non-imaging devices have been tested in research applications.
Background
The use of RNA has declined considerably with the proliferation and advancements in echocardiography. In fact, most of the exercise RNA literature is more than 2 decades old. At the time, interest in RNA produced fascinating data in the study of cardiac adaptation to exercise, the diagnosis and risk assessment of patients with CAD, the evaluation of patients with valvular and congenital heart diseases, the assessment of diastolic LV function in many patient populations, including those with hypertrophic cardiomyopathy, and the assessment of activation sequences via evaluation of phase and amplitude images using Fourier analysis of the time-activity curve (TAC) in each pixel within the ROI. One RNA study that remains popular is the serial assessment of LVEF in patients with several solid tumors who are undergoing chemotherapy with drugs that are associated with cardiotoxicity. In our daily practice, we continue to use RNA in patients in whom the 2DE is of poor quality or has results that are not consistent with clinical judgment, especially in potential candidates for device treatment (intracardiac defibrillators or biventricular pacing).
An additional factor that has contributed to the decline of RNA use is the ability to measure LVEF by gated SPECT myocardial perfusion imaging; this technique can also be used to assess dyssynchrony. These new developments happened at a time when tomographic gated RNA had reached a stage at which it could be implemented for routine clinical use. Along the way, other methods have come and gone, one of them being the nonimaging probe known as the VEST, a nuclear counterpart to the ambulatory Holter monitor, capable of measuring LVEF on a beat-to-beat basis. Other devices included the multiwire gamma camera and a short-lived, generator-produced tracer (tantalum-178).
The most frequently used variant of RNA is gated RNA, also known as a MUGA (multiple gated acquisition), performed in multiple planar projections. This method is popular because it can readily be done with a standard gamma camera. A MUGA can also be acquired in tomographic fashion (SPECT MUGA), which is superior to the planar method in delineating LV, and especially RV, topography, and volume measurements. The SPECT MUGA is now more widely used than traditional MUGA. We almost always perform both, as the tomographic method can be completed in a shorter period of time.
An alternative method is the first-pass RNA, with which we have had extensive experience. Unlike MUGA, it requires a dedicated gamma camera with a high counting efficiency for best results. Further, the first-pass method also inherently requires more skill and a larger vein for the bolus injection of the tracer. These issues, combined with the others discussed here, have limited its use.
In this chapter, we shall revisit some of these uses and developments in the following images and legends.
Case 4-1
Rest MUGA ( Figure 4-1 )
A 64-year-old woman is undergoing chemotherapy for breast cancer. She has a MUGA study. The images are shown in the LAO projection at end-diastole and end-systole ( Figure 4-1, A ). The LV function is normal.
In Figure 4-1, B , a 59-year-old man has severe LV dysfunction and is being considered for ICD therapy. The images in the anterior, shallow, and steep LAO projections are shown at end-diastole (top row) and end-systole (middle row) together with the time activity curve and its first derivative (bottom row). The LAO is used to derive the EF, as it allows for better separation of the LV and RV. A slight caudal angulation allows separation of the LV from the left atrium.
The dynamic images from a patient with heart failure symptoms are shown in Video 4-1.
Comments
The main indications for rest MUGA at our institution are serial studies in patients receiving chemotherapy for solid tumors and candidates for CRT/ICD therapy in whom the 2DE studies are, or are expected to be, of suboptimal quality.
Case 4-2
Rest First-Pass RNA ( Figure 4-2 )
This 43-year-old woman has a history of heart murmur and syncope. The images showed bolus transit through the central circulation and the LV silhouettes at end-diastole and end-systole with derived measurements. The EF is normal.
Comments
As mentioned, the 2DE in this patient was of suboptimal quality. This patient had aortic regurgitation; precise assessment of EF is critical in the timing of surgery to correct this problem.
Case 4-3
SPECT MUGA ( Figure 4-3 )
A 66-year-old woman was treated with chemotherapy for an ovarian tumor. The SPECT MUGA shows normal LV/RV function. In Figure 4-3, A , end-diastole frames in the short-axis projection, along with the volume-time curve and LV volumes, are shown.
In Figure 4-3, B, the SPECT MUGA of a 36-year-old man with dilated cardiomyopathy is shown in the same format. The 3D images at end-diastole and end–systole for both patients are shown in Figure 4-3, C , and the dynamic images are shown in Video 4-2, A, B.
Comments
The tomographic MUGA is superior to planar MUGA in assessment of LV topography and volumes and RV function.
Case 4-4
Rest and Exercise First-Pass RNA in a Normal Subject ( Figure 4-4 )
A 52-year-old man with atypical angina underwent rest and exercise first-pass RNA. The rest and peak exercise images are shown in a modified anterior projection (superimposed end-diastolic and end-systolic silhouettes). There is an increase in EF, EDV, SV, CO, and HR and a decrease in ESV. The wall motion becomes hyperdynamic during exercise.
Comments
First-pass RNA captures data at peak exercise (unlike MUGA, which provides averaged data acquired over 2 minutes) and has been very helpful in the understanding of cardiac adaptation to exercise and the roles of the Starling mechanism and increased contractility in the augmentation of LV function during exercise. Normal subjects increase the stroke volume by increasing the EDV and decreasing the ESV during peak exercise. The relative changes in these two parameters depend on age, intensity of exercise, gender, and body position, among other factors. The increase in cardiac output is due to increases in both stroke volume and heart rate.
Case 4-5
Rest and Exercise First-Pass RNA in a Patient With CAD ( Figure 4-5 )
A 72-year-old man with coronary risk factors underwent rest and exercise RNA. He developed angina during bike exercise and had 2-mm ST-segment depression in leads V 4 to V 6 . The images are in the same format is as in Figure 4-4, A . Unlike a normal subject, there is a decrease in EF, an increase in ESV, and marked LV dilatation with new severe wall motion abnormality.
