Nuclear Medicine/Nuclear Cardiology
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- 1 EKG stress testing
- 2 MUGA
- 3 Attenuation Correction
EKG stress testing
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Guidelines for EKG Stress Testing
- If the systolic BP is >200 or the diastolic >110 before exercise, the exercise test should not be done.
- In normal individuals, systolic BP can raise 160 to 220 mmHg. However, diastolic BP may not raise at all because the body is trying to open up the peripheral vessels to allow for the increased flow of blood rich with oxygen.
- If systolic BP falls by more than 10mmHg or if systolic BP does not exceed 130mmHg then this would be suggestive of myocardial damage. If the BP does indeed fall more than 10mmHg then the test should then be stopped if there is also other indications of ischemia.
- In any patient, if the systolic BP goes >250 or diastolic >115 then the test should be stopped.
- In normal individuals, exercise will raise blood pressure in order to supply extra oxygen to tissues. After exercise, the normal individual's blood pressure (BP) will quickly drop back down as the need goes away. However, in some individuals with ischemia, their BP will not drop rapidly. If at 3 minutes post-exercise the BP remains at approximately 90% of the maximum BP during exercise, this is a sensitive (>80%) but not specific indication of ischemia.
- More than a few things can cause excessive tachycardia during treadmill stress testing. However, at this time research has not outlined an objective quantitative prognostic value for what would be considered an abnormally high chronotropic response.
- The more coronary artery disease the patient has, the greater the sensitivity of ST depression in diagnosing ischemia.
- The "location" of the ischemia on EKG does not truly localize the area affected, with the slight exception of lead V1 (this assumes the leads were placed correctly).
- ST depression in contiguous leads (like V4-V5-V6) is more likely to be true ischemia.
- ST depression at maximal stress that corrects quickly after cessation of exercise is more likely to be a false positive. However if ST depression continues long after exercise (more than 8 minutes), it is more likely a true positive.
- T wave inversion that happens with ST depression is indicative of true ischemia.
- If ST depression comes after exercise (>2-3min) it is likely a false positive.
- True ischemia usually has an onset at a given rate and then goes away at the same rate.
- Chest pain that happens with ST depression is likely to be true ischemia.
- False positivity is more likely to happen in women, perhaps because women are less likely to have chest pain that is caused by cardiac ischemia.
- More than 1mm of "downsloping" or "horizontal" ST depression is more likely to be true ischemia.
- Upsloping ST depression, in general, is less likely to be a true event. However, if there is upsloping ST depression that is 1.5mm at or after 80ms (two small bars) from the J point, it is more likely to be true ischemia.
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Pharmacologic Stress Testing
- Medications such as Dipyridamole, Adenosine, and Regadenoson(Lexiscan) are used instead of exercise stress testing because they have the ability to "mimic" the hemodynamic state of the heart during normal stress. The primary mechanism of action is to dilate the cardiac vessels in general, thereby unmasking defects in vessels that may not be able to dilate and/or have blockage by atherosclerosis or plaque/embolus. See more detailed descriptions below.
- Dobutamine's mechanism of action is to directly produce stress by beta agonism and increasing chronotropic and inotropic activity in the heart. See more detailed descriptions below.
- A new medication that can be used instead of Adenosine for pharmacologic stress testing. It is "selective" for A2A receptors with lower affinity for receptors that cause unwanted side effects (A2B, A3, A1) It is reputed to be better tolerated by patients and has is a non-inferior stress agent to Adenosine.
- Indications - pharmacologic stress agent for patients that either cannot tolerate exercise portion entirely or has attempted exercise stress and is unable to reach optimal stress. There is a new suggestion that Lexiscan can be used as a primary agent without the need to fail the exercise portion first.
- Administration - 5mL quick bolus after a saline flush; wait 10 to 20 seconds then give stress radiotracer. All of these injections may go through the same IV access.
- Absolute Contraindications
- Second or third degree AV block or sinus note dysfunction (with the exception of patients that have a working pacemaker)
- Bronchospasm - patients with COPD or asthma should not use this med
- Systolic BP less than 90mmHg
- Dipyridamole use within 48 hrs.
- Aminophylline use within 24 hrs.
- Caffeine use within 12 hrs.
- Any known hypersensitivity to Regadenoson
- Relative Contraindications
- Sinus bradycardia less than 40 beats per minute.
- Advantages over Adenosine
- Reduced chance of error with single bolus dose of 0.4mg of medication in a 5mL syringe for all patients and does not require a pump infusion.
- Lower side-effect profile
- Less activity in receptors that cause adverse side effects (A2B, A3, A1)
- Less flushing 16% vs 25%
- Less 1st degree block than Adenosine (3% vs 7%)
- Less 2nd degree block (0.1% vs 1%)
- Disadvantages from Adenosine
- Dyspnea - Reputed to cause more dyspnea than Adenosine, especially in patients with COPD but not necessarily an increase in bronchoconstriction.
- Headache - causes more headache than Adenosine (26% vs. 17%)
- Adenosine can be easily cut off by stopping infusion at any time. The half life of Lexiscan is much longer and if there are severe or prolonged side effects, the patient must recieve IV Aminophylline to reverse the effects.
- When to give Aminophylline to halt side effects:
- Hypotension with SBP less than 80 BPM
- 2nd degree heart block that does not go away and is symptomatic or 3rd degree heart block.
- Chest pain with >2mm ST depression
- If patient asks to halt the test
- Quality of images compared to Adenosine and Dipyridamole are inferior because it does not create as large of a difference in blood flow in ischemic vs normal myocardium. Also, it is not as studied as the more traditional stress agents.
- Mechanism - Beta agonist of the Beta 1 and Beta 2 receptors to create increased chronotropic and inotropic stress on the heart.
- For patients that cannot tolerate Adenosine, Regadenoson, or Dipyridamole because of a contraindication.
- MI within last week.
- Pharmacologic Beta-Blockade
- Aortic dissection or sizeable aortic aneurism
- History of ventricular tachycardia
- Atrial tachyarrhythmias with uncontrolled ventricular response.
- Aortic stenosis that is severe
- Left ventricular outflow obstruction such as Hocm obstruction seen in hypertrophic cardiomyopathy.
- SBP >200 or DBP>110
- Main side effects
- Chest pain - 31%
- Palpitations - 29%
- Headache/flushing - 14% each
- When to terminate infusion and reverse with beta blocker
Please see reasons to terminate any exercise test.
- Ventricular tachicardia
- Of note: the likelihood of any ST depression is greater with dobutamine.
Ejection Fraction Monitoring with Doxorubicin
- Adriamycin (Doxorubicin) is a chemotherapeutic agent used in treating various cancers. It has been shown to cause significant impairment of cardiac function. The drug's effect can be measured well by the MUGA scan which is very accurate.
- Heart failure has been shown to develop in some patients at a cumulative dose of >500 mg/m², and the risk increases with even higher doses.
- It is shown that a decrease in EF will precede irreversible heart failure.
- Two factors are important in monitoring these patients, the absolute EF and the change in EF.
- If there is a >10% fall in EF below 50% or
- If there is an absolute EF of 40% or
- If there is a fall of >20% in EF at any time then there is said to be an impact by doxorubicin and the cessation of the medication should be considered based upon the given clinical scenario.
- There is some controversy about the accuracy of attenuation correction.
- It is commonly done with either a CT attenuation map or by gadolinium-153 source rods.
- ^ PMID 15998671 -- "Exercise testing in asymptomatic adults: a statement for professionals from the American Heart Association Council on Clinical Cardiology, Subcommittee on Exercise, Cardiac Rehabilitation, and Prevention." (Lauer M, Froelicher ES, Williams M, Kligfield P. Circulation. 2005 Aug 2;112(5):771-6. Epub 2005 Jul 5.)
- ^ PMID 19356442 -- "Effects of age, gender, obesity, and diabetes on the efficacy and safety of the selective A2A agonist regadenoson versus adenosine in myocardial perfusion imaging integrated ADVANCE-MPI trial results." (Cerqueira MD, Nguyen P, Staehr P, Underwood SR, Iskandrian AE; ADVANCE-MPI Trial Investigators. JACC Cardiovasc Imaging. 2008 May;1(3):317-20.)
BP - Blood Pressure BPM - Beats Per Minute DPB - Diastolic Blood Pressure EF - Ejection Fraction MI - Myocardial Infarction SBP - Systolic Blood Pressure