Update in Cardiac Stress Testing and Nuclear Cardiology

Matthew Schumaecker, MD, FACC, FASNCMedical Director, Nuclear CardiologyDivision of Cardiology, Carilion ClinicAssistant Professor of MedicineVTC School of Medicine

Objectives

After 50 minutes, the awake audience member should have:• A renewed conceptual framework of cardiac

stress testing• A better understanding of the epidemiology

behind stress testing, particularly nuclear cardiac testing

• An introduction to novel technologies in nuclear cardiology with emphasis on low-radiation techniques

Part I: What is Cardiac Stress Testing

Overview of Stress Modalities

Stress Modality• Exercise

• Treadmill• Bicycle

• Pharmacological• Dobutamine• Atropine

• Adenosine• Dipyridamole

Imaging Modality• Surface electrocardiography• Echocardiography• Myocardial Perfusion

Imaging:• SPECT• PET

Stress Modality: Exercise

Advantages:• Least expensive stress

modality• Lowest concern for

adverse reaction• Produces physiologic

ischemia in CAD• Threshold of reproduction

of ischemic symptoms• Derived functional data

is strongly predictive of cardiac mortality

Disadvantages:• Cannot perform in

patients with significant functional limitations

• ECG uninterpretable in LBBB, LVH, resting ST abnormalities, WPW, PPM and SPECT can be false positive in LBBB and patients with PPM

Stress Modality: Exercise-Treadmill

• Treadmill is most commonly used for exercise

• Bicycle is used mostly in echo lab for valve cases (i.e., mitral stenosis) and to assess for exercise-induced pulmonary hypertension.

• Patients are put on a standardized protocol which can predict performance based on age and gender (i.e., Bruce, Cornell, Naughton)

Stress Modality: Exercise-Treadmill

Bruce Protocol - Treadmill• Most commonly used

protocol.• Very well-studied and

validated with good prognostic data.

• Each stage lasts three minutes

• Patient exercises to symptomatic maximum

Stage Speed (mph)

Gradient (%)

I 1.7 10

II 2.5 12

III 3.4 14

IV 4.2 16

V 5.0 18

VI 5.5 20

Stress Modality: Exercise

• MET = Metabolic equivalent• 1 MET = amount of energy expended at

supine rest• 1 MET ≈ (kcal/hour)/kg• 1 MET ≈ 3.5 ml/kg/min VO2

• Average maximum exercise threshold in healthy middle-aged male ~ 10 METS

Stress Modality: Exercise-Treadmill

Stress Modality: Exercise-Treadmill

Stress Modality: Exercise - Bicycle

Advantages• More direct measurement of

work (i.e., watts)• Echocardiographic images

obtained during exercise• Useful for evaluating mitral

stenosis and exercise induced pulmonary hypertension

• Can complement vasodilator stress by producing better images and minimizing symptoms

• Can obtain respiratory data if

equipped

Disadvantages• Can be cumbersome to set up.• Takes longer to reach MPHR• Not widely used in US for

cardiac stress testing

Stress Modality: Dobutamine

• Beta agonist• Simulates exercise by positive chronotropy

and inotropy.• Can be difficult to achieve 85% MPHR with

dobutamine alone• May need to augment chronotropic response

with atropine up to 1 mg.• Can cause SAM and LVOT obstruction in

patients with significant septal hypertrophy.

Stress Modality: Vasodilator

Slide by Dr. Robert Hendel. ASNC 7/07

Stress Modality: Vasodilator

Slide by Dr. Robert Hendel. ASNC 7/07

Stress Modality: Adenosine

• Causes coronary arteriolar vasodilation• Extremely short half life• Given in a four or six minute infusion• Tracer is injected halfway through the

protocol• Can cause flushing, diaphoresis,

chest pain. Usually resolves within minutes after infusion

Stress Modality: RegadenosonFour Types of Adenosine Receptors

• A1 – AV Block

• A2A – Vasodilate small coronary vessels• A2B – Mast cell degranulation

• A3 - Bronchoconstriction

ADVANCE MPI-2

Mahmarian et al. JACC Imaging; Aug 2009

Stress Modality: Dipyridamole

• Trade Name: Persantine• Acts by blocking the cellular uptake of

adenosine• Four to ten times less expensive than adenosine• Comparable to adenosine with respect to

sensitivity; specificity may be lower• Much longer half life so adverse reactions tend

to be more severe• Not used very much in clinical practice

Imaging Modalities

Slide by Dr. Robert Hendel. ASNC 7/07

Surface ECG

• Obtained during every stress modality.• Determine underlying rhythm• Assess for arrhythmic response to stress• Assess for ischemic response to stress

• ST segment is monitored during all phases of stress to look for significant deviation.

• Sensitivity and specificity alone are lower than other modalities (especially in women) but can be complementary to other modalities.

ECG Positivity

Tak and Gutierrez. Postgraduate Medicine Online June 2004

Stress Echo

Pro• No radiation• Higher specificity• Can assess other cardiac

chambers and valves.• Can assess valve

disease• Can assess pulmonary

hypertension

Con• Operator-dependent• Lower sensitivity• No vasodilator option• Non-quantitative

Stress Nuclear

Pro• Higher sensitivity• Vasodilator option• Quantitative support• Less inter-operator and

inter-reader variability

Con• Radiation concern• Does not evaluate valves

or other cardiac processes other than myocardial perfusion

Part II: Why Do We Stress Test?

Part II: Why Do We Stress Test?

• Rule out CAD?• Reassure patients?• Reassure ourselves?• Avoid lawsuits?

Imaging Modalities:Sensitivity and Specificity

Tread

mill

ECG

Planar

Tha

llium

SPECT MPI

Tread

mill

Echo

PET0%

10%20%30%40%50%60%70%80%90%

100%

SensitivitySpecificity

Why Do We Stress Test?

• To provide a physiologically-based risk assessment in selected individuals which is adjunctive and additive to traditional risk assessment from H&P and models such as Framingham or Reynold’s Risk Score

Cardiac Death and MIby SPECT Degree of Normalcy

Hachamovitch R, Berman DS, Shaw LJ, et al. Circulation. 1998 Feb 17;97(6):535-43.

Black boxes– Cardiac deathWhite boxes – Myocardial infarction

n=5534

Cardiac Death Rate Stratified by Revascularization vs. Medical Therapy and by SPECT Degree of

Normalcy

Hachamovitch R, Berman DS, Shaw LJ, et al. Circulation. 1998 Feb 17;97(6):535-43.

Black boxes – Medical TherapyWhite boxes – Revascularization

Part III:Which Patients Do We Stress Test?

Part III:Which Patients Do We Stress Test?

• Patients at high risk for CAD?• Abnormal ECG• Hyperlipidemia• Hypertensives• Smokers

Why Detecting (asymptomatic) CAD Might Not Matter

Why Detecting (Asymptomatic)CAD Might Not Matter

Is there any role to stress testing asymptomatic individuals?

NOT USUALLY

“Special” Asymptomatic Indications

• Consideration for class Ic antiarrhythmic• Newly diagnosed cardiomyopathy• CT calcium score > 400 Agatston units• Chemotherapy• MAYBE – high risk (>20%/10 year)

diabetics

Appropriate Use Criteria

Appropriate Use Criteria

Part IV: Radiation Safety and Advances in Nuclear Imaging

Technology

Danger of increased radiation

• “ Myocardial perfusion imaging … now accounts for more than 10% of the entire cumulative effective (radiation) dose to the US population from all sources except radiotherapy.”

Einstein AJ. Effect of radiation exposure from cardiac imaging. J Am Coll Cardiol 2012; 59:553-565.

Society Mandate for Lower Radiation Exposure

The American Society of Nuclear Cardiology has set a goal that accredited nuclear cardiology laboratories should reduce radiation levels to 9 mSv in half of patients by 2014

Journal Nuclear Cardiology 2010; 17:709-718

82,861 patients studied after MI. 77% had cardiac imaging or procedure

For every 10 mSv of low-dose ionizing radiation, there was a 3% increase in the risk of age- and sex-adjusted cancer over a mean follow-up period of five years (hazard ratio 1.003 per mSv, 95% confidence interval 1.002–1.004).

Imaging procedures and their approximate effective radiation doses*

Procedure Average effective dose (mSv)

Range reported in the literature (mSv)

Bone density test+ 0.001 0.00–0.035

X-ray, arm or leg 0.001 0.0002–0.1

X-ray, panoramic dental

0.01 0.007–0.09

X-ray, chest 0.1 0.05–0.24

X-ray, abdominal 0.7 0.04–1.1

Mammogram 0.4 0.10–0.6

X-ray, lumbar spine 1.5 0.5–1.8

CT, head 2 0.9–4

CT, cardiac for calcium scoring

3 1.0–12

Nuclear imaging, bone scan

6.3 �

CT, spine 6 1.5–10

CT, pelvis 6 3.3–10

CT, chest 7 4.0–18

CT, abdomen 8 3.5–25

CT, colonoscopy 10 4.0–13.2

CT, angiogram 16 5.0–32

CT, whole body variable 20 or more

Nuclear imaging, cardiac stress test

40.7 �

Source: Mettler FA, et al. "Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog,"Radiology (July 2008), Vol. 248, pp. 254–63.

At Carilion, closer to 15.2 mSv

Spectrum Dyamics D-SPECT

Uses CZT (Cadmium Zinc Telluride) crystal instead of tradition NaI

This makes it much more sensitive to photon emissions

Analagous to taking a picture with very high speed film – you need less “light” to get a picture

This allow us to get clear pictures:•More quickly•With less radiation•On more obese patients (weight limit 531 lbs)

Solid State SPECT Imaging:Low Dose

Recent data shows that an excellent quality scan could be accomplished with 5 mCi of Technetium.

This would provide about 1.6 mSv of radiation per scan

Stress First/Only

• 60-70% nuclear studies normal• If stress images are normal, rest images

are not clinically valuable• In lower risk patients, we could do stress

imaging and only if abnormal bring back for rest

Radiation ExposureNormal BMI

Procedure Radiation Exposure

Dual Isotope Imaging traditional SPECT

24mSv

Same Isotope (Tc-Tc) Imaging/traditional SPECT

12mSV

Same Isotope (Tc-Tc) Imaging / D-SPECT

4 mSv

Stress Only (Tc) / D-SPECT 1 mSv

Questions

Matthew SchumaeckerBlackberry: 540-494-2411