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       Protocol for CT Angiography


 

Contraindications

 The following situations make it impossible to perform CT angiography:

  • an irregular  rhythm (e.g. atrial fibrillation, wandering atrial pacemaker, multifocal atrial tachycardia, frequent ectopy)
  • inability to lie still or hold breath for 15 secs
  • inability to follow verbal commands
  • renal insufficiency (creatinine > 1.5)
  • pregnancy
  • heavy coronary calcification (Agatston
    score > 1500)

In special situations, we may study patients with a creatinine up to 1.9 or Agatston scores >1500. Such patients require the approval of the cardiologist in charge prior to scheduling.


Premedication

Optimal image quality requires a HR <65 and most patients are pre-medicated with beta blocker. If possible and not contraindicated, we prefer the patient be prescribed metoprolol 50 mg po qhs and 2 hrs prior to exam.

When this is logistically impossible, we have the patient come 1.5 hrs before the schedule test, check the heart rate and any possible contraindications, give the patient metoprolol 50-100 mg po, and have them wait in our lobby for 1 hr before proceeding. 

If neither method has achieved optimal heart rate, we may give the patient up to 25 mg of additional metoprolol IV prior to imaging.

Unless contraindicated all patients are given sublingual nitroglycerin spray for maximal coronary dilation immediately prior to testing.


Test procedures

  • review clinical indications, serum creatinine, and radiation questionnaire
  • ECG leads and check of cardiac rhythm and HR
  • right antecubital IV (20 g or larger)
  • additional IV metoprolol prn HR <65
  • sublingual TNG spray
  • scout chest film
  • calcium score
  • timing bolus (20 ml contrast)
  • CT coronary scan (70-80 ml contrast)

 

Radiation exposure

Typical radiation doses for a CT coronary angiogram and other common tests are as follows: 

  • CT coronary angio                             5-12 mSv
  • CT of chest                                        5-7   mSv
  • nuclear perfusion stress test             6-35 mSv
  • cath/coronary angiogram                   5-10 mSv
  • chest radiograph                                <0.1 mSv
Whenever possible, dose modulation technology is used to minimize the radiation dose received by the patient.


 

 

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