Dobutamine MPI scan for heart | Super Sahyog Nuclear Imaging

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For most essential points to best prepare for the procedure, please download the patient information brochure (PDF).
For a more elaborate explanation of the procedure and related points, please continue to read ahead.

Brief introduction

Principle

This write up is best read after going through general introduction to MPI explaining functioning of the heart, its blood supply, and principles of this procedure.

Physical stress (e.g., based on treadmill) is the first choice for stress testing as it also tests effort tolerance, which is an independent prognosticator of cardiovascular health. However, in patients in who physical stress is not suitable (e.g,. inability to walk briskly or higher perceived risk of increased myocardial oxygen demand) and adenosine is also not suitable (e.g., because of uncontrolled asthma and COPD), dobutamine based stress test is used.

Dobutamine increases heart rate as well as force of heart contraction thus increasing myocardial oxygen demand similar to physical stress. Likewise, it also causes dilatation of the the intramural arteries. The blood flow through the stenosed epicardial arteries does not increase to the same degree as the relatively normal ones, and this heightened heterogeneity in blood flow between resting and post-stress states is detected through MPI.

The 'stress' part of the test involves continuously infusing dobutamine in escalating fashion over 12 to 15 min till target heart rate is achieved. Sometimes atropine could also be used in an attempt to raise the heart rate. The RP (MIBI or tetrofosmin) is injected with 2 minutes of infusion still remaining. Patient's heart rate and BP are monitored around and during the infusion period.

Indications (conditions in which advised)

Assessing need for CAG in those with intermediate test results on treadmill test.
Assessing need for CAG in those with renal failure.
Baseline assessment before medical therapy and/or revascularization (PCI or CABG surgery).
Assessing improvement in myocardial perfusion following treatment for CAD and/or IHD.
Evaluating viability of at-risk myocardium (though cardiac FDG PET is more reliable in this regard).
Determining prognosis after MI.
Preoperative stratification of risk for adverse cardiovascular events during non-cardiac surgery

Considerations / steps before procedure

Prior appointment is a must.
Patient must not be pregnant.
If breast feeding, please inform the staff for further directions.
Some drugs that alter heart rate and blood pressure (beta blockers, calcium channel blockers and nitrates) may have to be stopped few days before the procedure.
Caffeine-containing beverages and food products (i.e., tea, coffee, chocolate and certain 'cold drinks') must be avoided for 12 hours before the procedure.
Class of drugs called methylxanthines (most commonly used in asthma) must be stopped 24 hours before the procedure.
Male patients must shave off chest hair before reporting.
Wear loose-fitting but warm clothes.
Please bring along suitable fatty meal (e.g., bread and butter) for the procedure.
4 hours’ fasting before scan.
Please let the staff know at the time of appointment if the patient is unable to lie still for ~30 min, has breathing difficulty, or might need special medical attention for the duration of visit.
Have at least 1/2 litre water within an hour before reporting for the scan. There is no need to hold urine.
There is no need to hold urine before reporting for the procedure.
Do not bring expensive jewellery or accessories along with you for the scan.
Proof of doctor's request is necessary for starting the procedure.
The patient must be accompanied by a responsible carer.

What to expect as part of procedure?

Important steps

Rest study
1. Patient registration and consent.
2. Handing over medical documents to the staff.
3. Intravenous (IV) access is established (in form of cannula).
4. Radiopharmaceutical (RP) - Sestamibi / tetrofosmin is injected through the IV cannula.
5. Waiting time of ~75 min (± 15 min) to allow sufficient time for RP to be taken up and eliminated by all organs. Pass urine just before the scan, and also before that (if needed).
6. Scanning process starts wherein, the patient lies on their back on the scanner table. A pair of detectors rotates around the patient's chest region, and the entire procedure lasts for ~30 minutes.
7. The acquired images are reviewed to ascertain satisfactory scan quality.
8. The scan may have to be repeated especially if there is unacceptable patient movement.
Stress study
1. RP is injected during the dobutamine infusion (as described above).
2. Waiting time of ~75 min (± 15 min) to allow sufficient time for RP to be taken up and eliminated by all organs. Pass urine just before the scan, and also before that (if needed).
3. Scanning process is similar to the resting study.
4. The acquired images are reviewed to ascertain satisfactory scan quality.
5. The scan may have to be repeated especially if there is unacceptable patient movement.

Rest and stress studies can be performed on the same day or on separate days. Splitting study between 2 separate days could result in slightly better image quality and reduction in RP dose, but this could prove inconvenient to some patients.

Discomfort / risks during procedure

Pain during injections or IV cannula insertion.
There is risk of extravasation at the time of injections or IV cannula insertion. [Extravasation means that blood leaks through the walls of vein punctured by cannula’s needle].
There can be some transient side effects like palpitations, chest tightness, heaviness of head, headache, anxiety, etc. These usually completely resolve within 4 to 5 minutes of stopping dobutamine infusion.

Time taken for the entire patient visit

Typical: 5 hours (either on same day or split between 2 days).
Be prepared for: 7 hours (either on same day or split between 2 days).

What to expect after procedure?

Precautions / special care

Maintain at least 1 metre-distance from pregnant ladies and children (below 10 years) for at least 5 hours after the scan.
Drink plenty of water throughout the day (3 to 4 litres).
Pass urine as frequently as possible throughout the day.

Discomfort / risks

There can be blurring of vision for several hours (if atropine is used). So, avoid driving after the test.
There are no other remarkable expected risks or side effects.

Time taken for report / summary generation

Typical (for self-paying patients): 12 hours.
Be prepared for: 24 hours.

Additional reading

For additional information, please visit the following links.

Dobutamine MPI scan

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