Using safe, simple radionuclide techniques and sensitive detection equipment, we may calculate such indicators of function as cardiac output, cardiac index, mean pulmonary transit times, ejection fractions, and ventricular volumes. For many years we have been able to quantify left and right ventricular ejection fractions and ventricular volumes with simple techniques such as the gated radionuclide ventriculogram (MUGA) and gated SPECT myocardial imaging procedures. All four values may be obtained in minutes, though, with a radionuclide first pass exam. The precordial transit of radioactive blood can be tracked through the various cardiac chambers using highly efficient counting devices interfaced with a computer. This is a simple yet effective method for determining the presence of shunting, when there may be abnormal communication between chambers or vessels in the cardiovascular system.

DETERMINATION OF CARDIAC OUTPUT

Cardiac output can be defined as the effective volume of blood expelled by either ventricle per unit of time. It is usually expressed as milliliters or liters per minute. The output of either ventricle per beat is called the stroke volume. Expressed in terms of the stroke volume, the cardiac output (“CO”) would be equal to the stroke volume multiplied by the heart rate (“HR”).

CO (ml/ min) = SV (ml) x HR (beats/ min)

Cardiac output may be evaluated with radionuclide acquisition techniques. In normal individuals, the cardiac output averages 6.12 + 0.73 L/min with a range of 4.93 to 7.25 L/min. A more accurate indicator of output is the cardiac index, and takes into consideration the body mass of the patient, expressed in square meters. The patient’s height and weight values are input in the patient data information fields by the technologist prior to acquisition.

The cardiac index (cardiac output per square meter surface area) ranges from 2.75 to 4.10 L/min/m², with a mean of 3.36 + 0.35 L/min/m². The stroke volume or cardiac output per beat averages 92 + 14 ml/beat; the range is from 70 to 120 ml/beat. The stroke index, which represents the stroke volume/m², amounts to 50 + 7 ml/beat/m².

CIRCULATION TIME and SHUNTING

Circulation time represents the shortest interval between the intravascular injection of a substance and its arrival at some distant site in sufficient concentration to produce a recognizable end point. Radionuclides produce a sharp, well-defined end point that is identifiable objectively by specialized sensitive equipment. Measurement of circulation times is used as an aid to proper diagnosis of cardiovascular disorders and to determine the velocity of blood flow.

Estimation of the mean pulmonary transit time is an objective means of assessing the impairment of the pulmonary circulation caused by left-sided heart disease. This value may also be obtained with a first pass, in which a histogram is created based on a region of interest defined in the left lung field. Intracardiac shunts and anatomic abnormalities can also be easily assessed with this noninvasive technique.

LEFT VENTRICULAR EJECTION FRACTION

The ejection fraction is the best estimator of the overall pump function of the heart. Using safe, simple radionuclide techniques and sensitive detection equipment, we may calculate such indicators of function as cardiac output, cardiac index, mean pulmonary transit times, ejection fractions, and ventricular volumes. The precordial transit of radioactive blood can be tracked through the various cardiac chambers using highly efficient counting devices interfaced with a computer.

INDICATORS OF FUNCTION: CALCULATING VENTRICULAR VOLUMES, STROKE VOLUMES, CARDIAC OUTPUT AND CARDIAC INDEX MANUALLY WITH THE ROUTINE MUGA SCAN

Where does the functional information derive from when a MUGA is processed?  If your software doesn't give you a complete set of results, a skilled technologist with a hand-held calculator can run all the data manually using the following formulas.  For the inquisitive tech who would like to broaden their understanding of how things really work, I have transcribed my old manual MUGA processing notes from the 1980's when our El Scint computer had less than spectacular processing software. 

Worksheet:

A.   Patient and Acquisition Data

1. Height (cm)= inches x 2.54 cm/ inch

2. Weight (kg)= lbs ÷ 2.2 lb/kg

3. Room background counted for 2K, record time (sec) at same zoom LAO is acquired in.  

      T (sec)  = T (min)
        min
   

     2000 counts = Room background counts/min
       T (min)





4. Count patient blood sample taped to collimator for 10K, record time (sec).  Calculate syringe activity in counts per minute.
   
   

5. Record syringe activity in uCi.





6. Syringe CPM - Background CPM = Net activity CPM
   
   Net CPM ÷ ml in sample = syringe concentration CPM/ml
   
   

7. Heart Rate:  Total acquisition time (sec)  --->  Total counting time (min)
   
   
   Acquired R-R intervals  =  beats/min
   Counting time (min)
   
   
   

8. Total time in 1 frame:  Total acquisition time (min)  =  0._ _ minutes/frame
                                        16, 24 or 32 frames
   
   

9. Body surface area (square meters):  use height (cm), weight (kg) and chart

 

B.   LEFT VENTRICLE

1. ED counts:  total counts in LV at ED
   
   Area:  number of pixels in LV at ED
   
   

2. ES + BKG:  total counts in LV in ES frame using ED area
   
   

3. ES counts:  total counts in LV at ES
   
   Area:  number of pixels in LV at ES
   
   

4. High background may elevate EF values.  Background (K2 factor) behind LV:
   
   (ES + Bkg counts)  - (ES counts)  =  ___ cts/pixel
       ED area - ES area
   
   Used to create EF image and to analyze LVEF.
   
   
   

5. Stroke Volume:  Total ED counts in LV - (ES + bkg) counts
   
   
   

6. LVEF =         LV stroke volume counts            x 100 = LVEF
             (ED cts) - (K2 x total area of LV at ED)
   

 

C.  RIGHT VENTRICLE

1. ED counts:  Total counts in RV at ED
   
   Area: number of pixels in RV at ED
   
   

2. ES + bkg:  Total counts in RV in ES frame using ED area






3. ES counts:  total counts in RV at ES
   
   Area:  number of pixels in RV at ES
   
   

4. Background (K2 factor) behind RV:
   
   (ES + Bkg counts)  - (ES counts)  = ______________  cts/pixel
       ED area - ES area
   
   Used to create EF image and to analyze RVEF.
   
   

5. Stroke volume:  Total ED count in RV - (ES - bkg) counts

   
   
   

6. RVEF =         RV stroke volume counts            x 100 = RVEF
             (ED cts) - (K2 x total area of RV at ED)
   
   

 

D.  CALCULATIONS FOR LV

1. Left : Right stroke volume ratio=  SV counts LV
                                                SV counts RV   (1.00 + 0.20 is the normal range)





2. Overload of a ventricle
   
   If LV (< 20 is insignificant):  LVSV - RVSV    x 100= %
                                             LVSV
   
   If RV :  RVSV - LVSV    x 100= %
                 RVSV
   
   

3. Calculate total stroke volume (ml/beat)= Total SV counts/ T in 1 frame (min/frame)       ÷    (syringe conc. in cts/min-ml x 0.21 attn. factor)
                                                             
   
   

4. Cardiac Output (Liters/min):  LV SV (ml/beat) x HR (beats/min) x 1 liter/ 1000 ml





5. Cardiac Index (liters/min-m) = Cardiac Output (l/min) ÷ body surface area (m)





6. Volume of LV at ED (ml):  LVSV (ml/beat) ÷  LVEF (0.0x %)
   

 

E.  CALCULATIONS FOR RV

1. RV stroke volume (ml/beat)= Total SV counts/ T in 1 frame (min/frame)   ÷  (syringe conc. in cts/min-ml x 0.21 attn. factor)
                                           
   
   

2. RV volume at ED:  RVSV (ml/beat) ÷ RVEF (0.0x %)  or solve using overload value: % overload = (LSV - RSV) ÷ LSV, or RSV= LSV - (overload)(LSV)  then total volume of RV at ED = RSV ÷ RVEF .  Normal CI for RV= 3.2 L/ m