Unit 1 Lesson 2: Pharmacologic Stress Testing

What is a pharmacologic stress test echo? & so what can be assessed and detected?

A non-invasive diagnostic procedure that uses medication to simulate exercise so heart function can be assessed and potential coronary artery disease (CAD) can be detected.

List the 6 indications for a pharmacologic stress test.

• Inability to exercise

• Diagnosis of CAD

• Post-MI risk stratification (how much risk are they for another cardiac event to occur)

• Pre-op surgical assessment

• Myocardial viability

• Valvular heart disease

What is being evaluated when a pharmacologic stress test is used for myocardial viability?

Whether revascularization could improve myocardial contractility and EF.

List the 8 contraindications for pharmacologic stress testing.

• Unstable angina

• Severe anemia

• Electrolyte imbalance

• Uncontrolled arrhythmias

• Uncontrolled hypertension greater than 250/120 mmHg

• Liver failure

• Glaucoma — contraindication to atropine

• Severe bronchospastic disease

List the 6 advantages of pharmacologic stress testing.

1. Feasible for what patients

2. assessment of other abnormalities such as what list 2

3. what type of monitoring

4. Has Enhanced what?

5. Assessment of what?

6. Can assess the progession of what?

• Feasible for patients who cannot exercise

• Can assess other abnormalities, including valvular and myocardial abnormalities

• Continuous monitoring

• Enhanced safety

• Assessment of viability

• Assessment of progression of ischemia

List the 2 disadvantages of pharmacologic stress testing.

• No evaluation of functional capacity

• Time- and labor-intensive

How does dobutamine affect the heart?

Dobutamine directly stimulates the heart's beta-1 receptors, which:

• Increases myocardial contractility

• Increases stroke volume

• Raises cardiac output

List the 2 main reasons dobutamine is used for stress echocardiography.

• The patient is unable to exercise.

• ***Myocardial viability assessment — it is the most-used stress-echo modality for this purpose***

List the 5 standard dobutamine doses used during a stress echo.

1. 5 mcg/kg/min

2. 10 mcg/kg/min

3. 20 mcg/kg/min

4. 30 mcg/kg/min

5. 40 mcg/kg/min

Given starting at 5 mcg/kg/min & the dose increases at 3-minute intervals, with a maximum of 40 mcg/kg/min.

List the 4 low-dose dobutamine doses

1. 2.5 mcg/kg/min

2. 5 mcg/kg/min

3. 7.5 mcg/kg/min

4. 10 mcg/kg/min

Starts with 2.5 mcg/kg/min & the doses increase at 3-minute intervals, and the PowerPoint lists a maximum dose of 10–20 mcg/kg/min.

Standard dobutamine VS. Low-dose dobutamine doses what is the difference what does each one look for?

Standard dobutamine looks for ischemic changes

Low-dose dobutamine to look for myocadrial viability and contractility reserve

How does atropine affect the heart?

Atropine blocks M2 receptors located on the SA and AV nodes, causing:

• Increased heart rate

• Improved AV nodal conduction

What is the atropine dose, how often is it given, and what condition is it contraindicated in?

• Dose: 0.25–0.50 mg

• Given at 1-minute intervals

• Contraindicated in glaucoma because it can increase intraocular pressure

(0.50 mg is the max)

List the 4 situations when reversal medication should be used.

• Severe arrhythmias

• Severe hypotension or hypertension uncontrolled by other measures

• Severe chest pain, dyspnea, or ischemic ST changes

• Signs of decompensation or hemodynamic instability

List the 2 medications used to reverse dobutamine and their doses.

• Esmolol: 0.5 mg/kg over 1 minute

• Metoprolol: 5 mg IV

What medication is used first-line to reverse atropine, what is the dose, and what does it do?

Physostigmine is first-line.

• Dose: 0.5–1.0 mg IV over 1–2 minutes

• Restores vagal tone

• Slows the heart rate

When a medication restores vagal tone, it means the drug helps re-establish normal, healthy activity in the vagus nerve, which controls your body's parasympathetic nervous system (the "rest and digest" system).

List the 6 patient-preparation steps before a pharmacologic stress test.

• Patient NPO for 3 hours

• Obtain patient consent

• Explain the procedure and side effects of dobutamine

• Review cardiovascular history

• Place ECG leads for baseline 12-lead ECG and BP

• Place a 20-gauge IV for medication administration

List the 4 dobutamine side effects that should be explained to the patient.

• Palpitations

• Tingling

• Flushing

• Headache

List the 5 views obtained for baseline imaging at rest.

• Apical 4-chamber

• Apical 2-chamber

• Apical 3-chamber

• PLAX

• PSAX at the papillary-muscle level

What should be done after baseline images are obtained and before dobutamine administration?

Check the images with the physician before administering dobutamine. Then begin dobutamine infusion at 5–10 mcg/kg/min.

When are low-dose images obtained during the Aurora dobutamine protocol? & depending on the pt what?

Around 2 minutes after starting, depending on the patient's heart rate.

List the 5 dobutamine infusion levels used as the dose is increased during the Aurora protocol.

1. 5 mcg/kg/min

2. 10 mcg/kg/min

3. 20 mcg/kg/min

4. 30 mcg/kg/min

5. 40 mcg/kg/min

(Given starting at 5 mcg/kg/min) Increase dobutamine infusion by 10 mcg every 3 minutes until a maximum dose of 40 mcg/kg/min or 85% of maximum HR is achieved.

When may atropine be required during the dobutamine stress echo?

If the patient does not achieve 85% of their maximum heart rate.

When are peak-dose images acquired?

Once the patient reaches 85% of maximum heart rate.

List the 3 steps of the recovery phase after a dobutamine stress echo.

• Obtain recovery images after the medication is stopped, usually when HR is less than 100 bpm.

• Continue monitoring the patient after imaging has stopped.

• Continue BP and ECG assessment until the patient returns to baseline.

What is the normal response to dobutamine stress echocardiography? List 2 & The response is similar to what?

• Hyperdynamic wall motion

• Increased EF

The response is similar to exercise echocardiography.

List the 4 findings that may represent an abnormal response to dobutamine stress.

• Hypokinesia

• Akinesia

• Dyskinesia

• Or Failure of a wall to increase systolic thickening/excursion or an increase in LV volume

What is the normal regional response to dobutamine?

Marked hyperkinesis with increased velocity of contraction compared with rest and low-dose imaging.

What is the regional ischemic response to dobutamine? (base, mid, or apex)

Hypokinesis and decreased velocity of contraction compared with low-dose imaging and usually compared with rest

List the 3 findings of a normal global response to dobutamine.

• Decrease in EDV

• Marked decrease in ESV

• Marked increase in EF

List the 2 global ischemic responses to dobutamine.

1. Decrease in EF

2. Cavity dilation

These are described as infrequent with left-main or multivessel disease

These findings can happen with severe left-main or multiple-vessel CAD, but they are not commonly seen.

So, simply:

Severe widespread ischemia → the whole LV may weaken → EF drops and the LV cavity may dilate, but this global response is uncommon.

How is pacing used to perform a stress echo?

The pacing rate is increased to achieve the target heart rate.

• Starts at 100 beats/min

• Increased by 10 beats/min every 2 minutes

• Continued until target HR is achieved

List the 2 important points about wall motion and dobutamine use during pacing stress echo.

• Pacing can cause dyssynchrony and RWMAs, but myocardial thickening can still be evaluated.

• Pacing may be combined with DSE to add an inotropic response to stress.

Because pacing mainly increases the heart rate, but it does not always make the heart contract much harder.

Dobutamine adds an inotropic response, meaning stronger heart muscle contraction.

So combining pacing with DSE gives the heart more complete stress:

• Pacing → increases HR

• Dobutamine → increases contractility

• Together → increase myocardial oxygen demand more, which can make ischemia easier to detect

So the simple idea is: we want the heart to work harder so hidden coronary artery disease is more likely to show up on the stress echo.

List the 6 stages of the dobutamine/pacing stress echo protocol (just nice to know)

what is the max Dobutamine Dose ? How many minutes is each stage?

1. Stage I: Dobutamine 5 mcg/kg/min

2. Stage II: Dobutamine 10 mcg/kg/min

3. Stage III: Dobutamine 20 mcg/kg/min

4. Stage IV: Dobutamine 20 mcg/kg/min + pacing to 70% of age-predicted max HR

5. Stage V: Dobutamine 20 mcg/kg/min + pacing to 85% of age-predicted max HR

6. Stage VI: Cooldown

Each stage is 3 minutes., max Dobutamine Dose 20

Images are acquired so any difference RWMA between pace and non pace rythm could be assessed looking at the difference between a pace rythm and non pace

What is the purpose of myocardial viability testing?

To determine whether revascularization could improve myocardial contractility and LVEF.

Revascularization means restoring blood flow to the heart muscle by opening or bypassing a blocked coronary artery.

List the 3 types of myocardium discussed in myocardial viability and define each one.

• Stunned myocardium: temporarily dysfunctional but alive

• Hibernating myocardium: chronically underperfused

• Scarred myocardium: non-viable tissue

What happens when myocardial ischemia is severe and prolonged?

It can cause myocardial necrosis, resulting in no return of contractile function.

What is stunned myocardium, and when does function recover?

When ischemia is relieved by reperfusion before necrosis occurs, the myocardium may become temporarily dysfunctional or stunned. Function can recover over days to weeks.

What is hibernating myocardium, and what may restore its function?

Chronic low blood flow and repeated stunning can cause metabolic adaptation and hibernating myocardium. Revascularization may eventually restore function, which can take weeks to months.

Myocardial hibernation is an adaptive response where the heart muscle reduces its contraction and energy use to survive long-term, low blood flow without dying

List the 4 myocardial responses that may be seen during dobutamine viability testing.

• Monophasic or sustained response

• Biphasic response

• Nonphasic response

• Ischemic response

What happens during a monophasic or sustained response at low-dose dobutamine?

The segment is abnormal at rest,

At low dose:

• Contractility mildly increases.

• O₂ demand remains low.

• Viable myocardium demonstrates contractile reserve, such as going from hypokinetic to normal.

What does it mean if myocardial function improves at low-dose dobutamine and continues to improve? (Monophasic response)

It represents viable myocardium, such as stunned myocardium.

List the 3 findings during Phase 1, or low-dose, of a biphasic response.

Abnormal segments at rest with a low does:

• Mild increase in contractility

• O₂ demand remains low

• Viable myocardium demonstrates contractile reserve, such as hypokinetic to normal

What happens during Phase 2, or higher-dose, of a biphasic response?

Heart rate, contractility, and oxygen demand increase. The myocardium is better at low dose but worsens at higher dose.

What type of myocardium produces a biphasic response, and why is this important?

Hibernating myocardium. It is both viable and ischemic, making it the best response for revascularization.

List the 3 findings of a nonphasic response.

The myocardium is:

• No thickening at rest, low dose, or peak imaging

• Scarred myocardium

• No myocardial viability

List the 3 characteristics of an ischemic response during dobutamine testing

• The myocardium may be normal or abnormal at rest.

• Function worsens without contractile reserve.

• Suggests stress-induced myocardial ischemia.

Ischemic response = the heart muscle gets worse when stressed because it isn’t getting enough blood flow.

• Normal or abnormal at rest: The heart wall may look normal or already weak before stress.

• Worsening of function: During stress, that part of the heart squeezes less well than it did at rest.

• Without contractile reserve: It cannot increase its squeezing strength when stressed

List 2 other pharmacologic testing

1. Dipyridamole/Adenosine

2. Ergonovine

List the 2 effects of Dipyridamole/Adenosine during a stress echo.

• Vasodilates the coronary arteries

• Mimics exercise by increasing coronary blood flow and myocardial perfusion

List the 3 contraindication categories for Dipyridamole/Adenosine stress echo.

• Hypotension

• Severe airway obstruction, such as COPD or asthma

• Certain heart-rhythm disorders

What does ergonovine do, and where is the test usually performed?

Ergonovine is a smooth-muscle constrictor. Testing is usually performed in the cardiac catheterization lab, although the medication can be given by IV bolus.

Smooth muscle constrictor = causes the muscle in blood vessel walls to tighten, narrowing the vessel.

What is the ergonovine dosing protocol?

Give 50 mcg of ergonovine maleate every 5 minutes until:

• Myocardial ischemia is detected, or

• A total dose of 0.35 mg is reached.