CARDIAC DIAGNOSTICTESTING

BY DR : RAMY A. SAMY

• CARDIAC BIOMARKERS • RADIOLOGY• ECG AND STRESS ECG • ECHO

Cardiac biomarkers • CK (CPK)• CK-MB• Troponin-I/T• LD (LDH)• Myoglobin• ALT/AST• Others

Creatine Kinase

an enzyme expressed in a number of tissues.

Function: it catalyses the conversion of creatine to phosphocreatine degrading ATP to ADP

The CK enzyme consists of two subunits, • B (brain type) or• M (muscle type), • Making three different isoenzymes: CK-MM, CK-BB

and CK-MB

ck

• Needs >two-fold increase with simultaneous increase in CK-MB to be diagnostic for MI

• Increases 4-6 hours after onset of MI• Peak activity is at 18 to 24 hours• Usually has returned to baseline levels by 36

hours

• False positive (for MI) CK elevation can be seen in:– Significant skeletal muscle injury– Significant CNS damage (Stroke/Trauma)–Occasionally from GI, renal, urologic disease

CK-MB

High specificity for cardiac tissueBegins to rise 4-6 hours after onset of

infarctionPeaks at about 12 hoursReturns to baseline at 24-36 hours

• False positive (for MI) CK-MB elevation can be seen in:– Significant skeletal muscle injury– Cardiac injury for reason other than MI• Cardioversion, Defibrillation (ACLS CPR/ICD

firing)• Blunt chest trauma (MVA/Sports injuries)• Cardiac AND non-cardiac surgical procedures• Cocaine abuse (vasospasm, tachycardia,

perfusion/demand mismatch)• Non often elevated in myocarditis, unless

severe

Troponin• Troponin is a complex of three regulatory

proteins that is integral to non-smooth muscle contraction in skeletal as well as cardiac muscle

• Troponin has three subunits, TnC, TnT, and TnI

–Troponin-C binds to calcium ions to produce a conformational change in TnI

–Troponin-T binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex

–Troponin-I binds to actin in thin myofilaments to hold the troponin-tropomyosin complex in place

• Thus far, studies have failed to find a source of Troponin-I outside the heart, but have found some Troponin-T in skeletal muscle• Because of it’s increased

specificity, our lab uses Troponin-I

• Troponin-I levels begin to rise 2-3 hours after onset of MI and roughly 80% of patients with AMI will have positive values at 3 hours

• Elevations in Troponin-I and Troponin-T can persist for up to 10 days after MI

• Therefore it has good utility for retrospectively diagnosing AMI

• Remember, CK-MB returns to baseline by 48 hours

• Troponin release can also be precipitated by other conditions that cause myocardial damage

• LD (LDH)

– Used in the past along with aminotransferases to diagnose AMI. LD is non-specific for cardiac tissue, which contains LD-1.

– However, pancreas, kidney, stomach tissue and red cells also contain LD-1.

– In the setting of AMI, LD rises at about 10 hours, peaks at 24-48 hours, and remains elevated for up to 8 days

• Myoglobin

– small-size heme protein released from all damaged tissues. Increases often occur more rapidly than TI and CK.

–Not utilized often for AMI/cardiac damage assessment because of its very rapid metabolism (short plasma half-life) causing short burst increases that are difficult to assess clinically, as well as its lack of specificity for cardiac tissue.

• ALT/AST– not used for assessment of myocardial damage any longer

• H-FABP– Heart-type fatty acid binding protein– Kinetically similar to myoglobin but more specific to cardiac

tissue which contains a greater percentage of this protein than skeletal muscle

– May also have role in prediction- prognosis in patients with NSTEMI

– Current studies ongoing to further evaluate its utility

Radiology

CARDIAC CATHETERIZATION

• DESCRIPTION

• These procedures involve insertion of a specialized catheter into the systemic circulation and advancement into individual coronary arteries or retrograde advancement across the aortic valve and into the LV.

• Following placement of the catheter in the desired location, hemodynamic data can be acquired, and angiography can be performed by injection of radiocontrast dye and fluoroscopic image acquisition.

• Catheterization is primarily used to diagnose obstructive coronary artery disease, assess its severity, and design the optimal medical and/or surgical treatment.

NUCLEAR IMAGING

NUCLEAR IMAGING• Nuclear myocardial perfusion imaging is

occasionally obtained in conjunction with stress testing to further aid diagnostic accuracy.

• This is especially useful in patients with baseline ECG abnormalities.

• The technique involves injection of a radioactive isotope that is extracted from plasma by viable myocardium. (technetium 99m [99mTc] sestamibi or 99mTc tetrofosmin),

• The images are acquired with a special camera that captures radioactive emissions.

• The intensity of the image is proportional to the perfusion of the myocardium

• Images are acquired both at rest and after peak-exercise or vasodilator infusion .

• The images are then compared, and stress-induced perfusion defects identified.

• The defects correlate with the presence of epicardial coronary artery disease.

• The use of myocardial perfusion imaging increases the accuracy of stress testing for diagnosing coronary artery disease.

Gamma Camera

• ELECTROCARDIOGRAM

CHAMBER ENLARGEMENTLEFT ATRIAL ENLARGEMENT CRITERIARIGHT ATRIAL ENLARGEMENT CRITERIAECG CRITERIA FOR LEFT VENTRICULAR

HYPERTROPHYECG CRITERIA FOR RIGHT VENTRICULAR

HYPERTROPHY

ECG CRITERIA FOR ACUTE MYOCARDIAL INFARCTION

EXERCISE STRESS TESTING

EXERCISE STRESS TESTING

• DESCRIPTION : • The exercise stress test (EST) is most

commonly used to diagnose coronary artery disease in low- to intermediate-risk patients.

• The EST is also used to assess exercise capacity and functional reserve in patients with known coronary artery disease.

• The test employs physical exercise (treadmill, stationary bicycle, or arm crank) in a controlled environment coupled with continuous telemetry monitoring and serial electrocardiographs (ECGs) to evaluate for evidence of myocardial ischemia.

Serial hemodynamic measurements are also obtained to determine the physiologic response to exercise.

• Stress testing is often performed in conjunction with an imaging modality to increase the sensitivity for detecting coronary artery disease.

INDICATIONSTo diagnose coronary artery disease (CAD) in

adult patients

To risk stratify

To assess the efficacy of medical treatment

To evaluate exercise capacity and functional status in patients with valvular heart disease.

CONTRAINDICATIONS• Absolute contraindications to stress testing

include the following: Acute MI (within 2 days) High-risk unstable angina Uncontrolled cardiac arrhythmias Symptomatic severe aortic stenosis Decompensated heart failure Acute pulmonary embolus Acute myocarditis or pericarditis Acute aortic dissection

Relative contraindications to stress testing include: Known left main coronary artery stenosis Moderate stenotic valvular heart disease Electrolyte abnormalities Severe arterial hypertension (systolic blood

pressure [SBP] >200 or diastolic blood pressure [DBP] >100)

Tachyarrhythmias or bradyarrhythmias Hypertrophic cardiomyopathy High-grade atrioventricular (AV) block Exercise intolerance

DISCONTINUING A TESTAbsolute indications for discontinuing an exercise test include the following:

Decrease in SBP >10 mm Hg from baseline

Moderate to severe angina

Development of central nervous system abnormalities (ie, ataxia, dizziness)

cyanosis or pallor

difficulty in monitoring the ECG or blood pressure

Sustained ventricular tachycardia

ST elevation >1 mm in any lead without significant Q waves

ECHOCARDIOGRAPHYDESCRIPTION• Echocardiography is a noninvasive modality that

utilizes reflected sound waves to image the heart and define both its structure and function.

• Two-dimensional echocardiography is used to assess cardiac structure, left ventricular function, valvular integrity and function, and the pericardium. It also permits calculation of chamber dimensions, areas, and volumes.

• Color flow imaging assigns different colors to blood that is moving toward the transducer (red) and away from the transducer (blue).

• It is used to detect abnormal flow such as valvular regurgitation, intraventricular shunts, and obstruction of flow within or between the cardiac chambers

• Contrast echocardiography

• Agitated saline

• INDICATIONS

Evaluation of murmurs and valvular heart disease.

Evalution of patients with established valvular heart disease.

Evaluation of prosthetic heart valves .

Chest pain and suspected ischemic heart disease.

Left ventricular function, pericardial disease, and miscellaneous.

Pulmonary disease.

Arrhythmias , palpitations and syncope .

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TRANSESOPHAGEAL ECHOCARDIOGRAPHY

• A similar study to a surface echocardiogram, however, the ultrasound probe is passed into the esophagus to examine the cardiac structures in close proximity.

• Transesophageal echocardiography offers superior assessment of cardiac anatomy and physiology because of the proximity of the probe.

STRESS ECHOCARDIOGRAPHY

• Echocardiography is often used as an imaging modality to increase the sensitivity and specificity of exercise

• stress tests for the detection of CAD. • Stress echocardiography also assesses

myocardial viability in patients with known CAD and in whom revascularization is being considered.