nuclear medicine in cardiology

Nuclear Medicine in Cardiology

Department of Nuclear MedicinePadjadjaran University – Dr. Hasan Sadikin Hospital

A. Hussein S. Kartamihardja

What does the heart do ?


• The heart is a powerful muscle consisting of two pumps side by side.

• Its steady beating maintains flow of blood to all parts of the body throughout life.

ECG/ Treadmill RadiographyEchocardiographyCT scanMRIAngiographyRadionuclide imagingRadionuclide imaging

Diagnostic modalities in heart disease

Cardiac Nuclear Medicine

Instrumentation

Radiopharmaceutical

Physician


History of nuclear cardiologyHistory of nuclear cardiology

Blumgard and Weiss (1927) :

the first use of radioactivity in the study of the cardiovascular system

Wilson : measurement of the circulation times

Tl-201 (1971)

The development and improvement of SPECT

The development and established Tc-labeled agents

Alternative stress than physical exercise

Gate-spect allows simultaneous assessment both of myocardial perfusion, function and assessment of myocardial viability

Gamma camera coincidence imaging system

Myocardial metabolic imaging


The ideal perfusion radiopharmaceutical

Distribution in the myocardium in linier proportional to blood flow.Efficient myocardial extraction from blood on the first passage through the heartStable retention within myocardium during data acquisitionRapid elimination allowing repeat studies under different conditionsGood imaging characteristics (short half life, low radiation burden to the patient)Ready availabilityCompetitive pricingNo current tracer possesses all of these properties.

Distribution in the myocardium in linier proportional to blood flow.Efficient myocardial extraction from blood on the first passage through the heartStable retention within myocardium during data acquisitionRapid elimination allowing repeat studies under different conditionsGood imaging characteristics (short half life, low radiation burden to the patient)Ready availabilityCompetitive pricingNo current tracer possesses all of these properties.


Thallium-201

Tc-99m Teboroxim

Tc-99m MIBI

Tc-99m Tetrofosmin

Thallium –201 Basic Properties

A metallic element which behaves chemically in a similar manner to potassium and is given as thallous chloride Photon energy is low, and 88% of its emissions are x-ray with photon energy of 60-80keV Gamma photons of 135 and 167 keV (12%)Enter myocyte by 60% active transport via Na+/K+ ATPase pump 40% passively along the electrochemical gradient

Distribution within the myocardium is proportional to blood flowThe half life of elimination within the heart is approximately 7 hrs


Tc-99m MIBI (methoxyisobutylisonitrile) Tc-99m TETROFOSMIN (Basic

Properties)

It is lipophilic

Distribution within the myocardium is proportional to blood flow

Diffuses out of the capillary into cardiac myocytes and is associated with mitochondria within the cell.

Cardiac uptake is depend on normal mitochondrial function.

Liver uptake of tetrofosmin is not as prominent as with Tc-99m MIBI

No redistributionDepartment of Nuclear MedicinePadjadjaran University – Dr. Hasan Sadikin Hospital

Correlation between Tl-201 and Tc-99m tetrofosmin imaging


Diagnosis & prognosis

Risk stratification

Medical vs. surgical treatment

Efficiency of management

Clinical application of Nuclear Cardiology


• CAD• Acute and post MI• Cardiomyopathy• Valvular disease and Shunts• Cardiotoxicity• Aneurysms• Transplants

Stress-rest Tl-201 and Tc-99m labeled agents has been widely used in the diagnosis and assessment of coronary artery disease

MPI still an important position in clinical practiceonly 1/3 of symptom-free men with exercise induced ST segment depression had coronary angiographic lesions > 50% diameter stenosis

MPI has been proposed to improve the accuracy and risk assessment of exercise testing in patients with suspected CAD

Sensitivity 74% - 96%, specificity 65% -97%

Principles of myocardial perfusion imaging ?Principles of myocardial perfusion imaging ?


• What is coronary artery disease ?What is coronary artery disease ? • A condition where there is progressive damage to the vessel wall

supplying the coronary arteries.• Unbalance between demand and supply O2 to myocardium

Imaging at 24 hrs is sometimes performed when the question of underestimation of myocardial mass in the redistribution images is clinically important

Cardiac stress test

Physical exercises Exercise has to be adequate to produced the heterogenity in

blood flow to achieve high detection sensitivity Treadmil Ergocycle

PharmacologicalPharmacological stress test become important, since many patients are unable to exercise

Pharmacological stress agents largely remove the need for patient cooperation and motivation, and enable a confident assessment of cardiac function in virtually all cases Dipyridamole Dobutamine Adenosine


Dipyridamole

Coronary artery dilator

The effects of dipyridamole include a mild decrease in systolic BP, slight increase HR.

The side effects include flushing, abdominal pain, nausea, vomiting, transient AV block and bronchospasm

Infusion dose of 0.56 mg/kg over four minutes (0.14 ml/kg/min)


DobutamineDobutamine

The ß-agonists increase myocardial oxygen demand through a combined inotropic and chronotropic action

It dilates the distal coronary vessels, which leads to an increase in coronary flow

Dose up to 40 ug/kg/min (commence at 10 ug/kg/min and proceed in 10 ug/kg/min step every 3 min)

Non-cardiac symptoms cause by dobutamine include tingling, flushing, nausea, headache, shaking and lightheadedness


Adenosine

Is a naturally occurring purine which mediates the cellular action of dipyridamole

No significant difference between the coronary hyperemic response to adenosine and dipyridamol

Has very short half life of between 2 – 10 seconds

Maximal coronary vasodilatation is achieved in 85% of patients with intravenous dose of 140ugr/kg/min

Side effect are similar to those with dipyridamol


Spect imaging

In SPECT imaging, the heart is viewed in 3 planes :

1. The horizontal long axis, which is parallel to the long axis of the heart from base to apex. It begins at the inferior aspect of the heart and progresses superiorly

2. The vertical long axis, which is perpendicular to the horizontal long axis. It begins at the lateral aspect of left ventricle and proceeds medially through the septum

3. The short axis of the heart which is perpendicular to both of the long axes. It begins at the base of the heart and progress through the mid plane to the apex


Image interpretation

I. Defects Location Extent Severity Reversible or fixed Quantitative or semi quantitative analysis

II. Other information Transient ischemic dilation Lung uptake


Normal perfusion scan


There is a wide variety of normal appearances arising from variation in size and position of the heart, body size and quality of tomographic acquisition

Knowledge of these variation and confidence in their identification is vital to prevent the reporting of defects as normal variant

An important issue to bear in mind if difficulty arise in distinguishing normal variants from true defects

G 2121-00


PRE-PTCA POST-PTCA

Differences between stress and rest/redistribution imaging indicates reversibility (ischemia)

M724499


ANGIOGRAM: A STENOSIS AT THE PROXIMAL AND MIDDLE THIRDS OF THE LAD ARTERY

PATIENT NO : M724499SEX : MALEAGE : 53 YRS

CLINICAL INDICATION : TWO ACUTE CORONARY EPISODES

S 0585/01

NO : S 0585/01 SEX : MALE AGE : 60 YRS ECG : NON Q-WAVE MYOCARDIAL INFARCTION


REST MPI SPECT GATED BLOOD POOL

Comparison between SPECT and Treadmill exercise test

Variable SPECT Treadmill

Availability ++ ++++

Cost ++++ +

Familiarity ++ ++++

Accuracy +++ +

Localization ++++ +

Extent of disease ++++ +

Viable myocardium ++++ +

Left ventricular function ++++ +

Risk assessment ++++ +


Risk Stratification


• Nuclear cardiology separates high risk patient who need invasive and expensive procedures and low risk patient who do not.

• Acts as a ”Gate - Keeper” for referral to angiography.

Outcome following non-fatal MI :Low risk group50% - 66% of the patientsCan be managed with medical treatment

High risk group34% - 50% of the patientsProne to future complications with 3 months death, re-infarction, CHF and unstable angina

Separation of high and low risk groups :

• Clinical evaluation• Rest and stress ECG*• Rest and stress RNA*• Rest and stress MPI*• Rest and stress echo• Angiography

• Recommended by ACC & AHA Task Force

Myocardial perfusion scan findings associated with increased risk for cardiac events after acute

myocardial infarction

Perfusion defects induced by exercise or pharmacologicalReversible perfusion defects in multiple coronary vascular territoriesLarge perfusion defect sizeImproved reperfusion after Tl-201 reinjectionIncreased lung uptakeLeft ventricular cavity dilatationLeft ventricular dysfunction on gated myocardial perfusion scanAbnormal right ventricular uptake


Myocardial Viability / HibernationMyocardial Viability / Hibernation


Persistently impaired myocardial and left ventricular function at rest, due to reduced coronary blood flow. (Rahimtola)

The functional abnormality can be partially or completely restored to normal by reducing myocardial oxygen demand and/or increasing coronary blood flow

Myocardial dysfunction is expected to be irreversible in regions with myocardial scar, but can be improved in region with ischemic but viable or hibernating myocardium.

The determination of myocardium viability in patients with CAD and the LV dysfunction has become a frequent issue since interventional cardiology is growing rapidly.

The differentiation of scar from hibernating myocardium is important.

Up to now, radionuclide myocardial imaging holds the most important promise in this field.

Metabolic measurement by PET may be the most sensitive non-invasive approach for the evaluation of myocardial viability.

Myocardial ViabilityMyocardial Viability


Why separate viable from scar tissue ?

• Surgical treatment for viable myocardium results in 11.5% event rate compared to 50% after medical treatment

• Surgical treatment for poor viability and scar have survival rate of 79% compared to 97% with viable tissue

LVD due to viable tissue have worse prognostic than scars with annual survival of 50% compared with 92% (PET data)

Techniques for assessing myocardial viability

Regional wall motion evaluation Ventriculography (gated spect) Echocardiography (dobutamine) Radionuclide angiography Magnetic resonance imaging

Perfusion and cell membrane integrity Tl-201protocols Tc-99m sestamibi Tc-99m tetrofosmin Nitrate-augmented perfusion imaging

Assessment of metabolism Well established for predicting functional recovery after

revisualization F-18 FDG I-123 fatty acids (IPPA, BMIPP)


Historical BackgroundNuclear Cardiology as “ a better stress test ” Detection of CAD as a benchmark for successGold standard : coronary angiography

Cost Effectiveness of Nuclear Cardiology


Misconceptions• Expensive stress test• Sensitivity < 100%• False positive• Imperfect correlation

with angiography

The changing paradigm• Angiography provides information on anatomy• Nuclear cardiology provides information on

function/physiology• Physiology is as important as anatomy, and

perhaps more important• Functional testing with nuclear imaging

provide comparable prognostic information at lower cost than angiography, non-invasive

• Information provided by nuclear cardiology can reduce cost and optimize treatment

MPI has been widely used and an important position in the diagnosis and assessment of CAD Sensitivity 74% - 96%, specificity 65% -97%

Summary


• Nuclear cardiology separates high risk patient who need invasive and expensive procedures from low risk patient who do not.

• Acts as a ”Gate - Keeper” for referral to angiography.

Cost of management strategies using MPI are cheaper and equally effective when compared with strategies without MPI with same outcome.

Nuclear cardiology separates persistent defect with LV dysfunction but viable myocardium from scar tissue


Thank you !

nuclear medicine in cardiology

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