Chapter 8CARDIOVASCULAR SYSTEM :Chapter 8CARDIOVASCULAR SYSTEM Page 129 - 189


Slide 2:Evaluation of coronary artery perfusion with various myocardial perfusion radiopharmaceuticals Assessment of ventricular pump performance employing gated equilibrium blood pool (MUGA) or first transit methodology Diagnosis and evaluation of acute myocardial infarction


Anatomy :Anatomy The heart’s approximate dimensions are: width, 9 cm; length, 12 cm; and depth, 6 cm. Normal coronary blood flow: 0.6 – 0.8 mL/min/g Blood flow may increase 4 – 6 times with stress, both exercise or pharmacologic When narrowing of a coronary vessel diameter is less than 50% the effect on blood flow is clinically insignificant


Anatomy :Anatomy Right (RCA) Inferior wall Variable protion of the interventriculare septum Left coronary artery (LCA) Left anterior descending (LAD) Interventricular septum anteriorly Anteriollateral wall Left circumflex (LCX) Posterolateral wall


Anatomy :Anatomy The left circumflex artery is found in the coronary sulcus between the left atrium and the left ventricle. The left anterior descending coronary artery is in the anterior intervenvicular sulcus that courses over the interventricular system, which separates the right and left ventricles. It passes around the apex and continues in the posterior interventricular sulcus on the diaphragmatic surface of the heart.


Anatomy :Anatomy Left Ventricle the wall thickness of the left ventricle is between 8 and 15 mm except for the upper third of the septum.


Anatomy :Anatomy Left Coronary Artery divides into the anterior descending and circumflex rami rare instances a single major vessel arising from the anterior descending coronary artery crosses diagonally over the anterior wall of the right ventricle anterior descending artery generally curves around the apex of the left ventricle into the postenor interventricular sulcus and extends to the posterior surface of the left and right ventricles.


Anatomy :Anatomy Left circumflex artery generally provides branches to the posterior surface of the left ventricle, and in 10% of human hearts it continues posteriorly. In such hearts, branches of the left coronary artery supply the entire left ventricle and interventricular septum.


Anatomy :Anatomy Right coronary artery 90% of human hearts the right coronary continues past the margin of the right ventricle into the posterior right AV sulcus. It branches posteriorly toward the apex of the heart and with its descending branches along the diaphragmatic surface of the left ventricle


Physiology :Physiology Cardiac cycle complete heartbeat consists of a contraction (systole) and relaxation (diastole) of both atria and ventricles Cardiac performance cardiac perfomance is the result of four determinants: preload, afterload, myocardial contractility, and heart rate


Physiology :Physiology Preload presystolic and end-diastolic volume Afterload arterial resistance against which the ventricle contracts Myocardial contractility speed and shortening ability of the myocardium, dependent on loading conditions


Physiology :Physiology Heart rate rate at which the heart contracts Myocardial oxygen requirement receives 10 % of the cardiac output extracts 70% of the oxygen in every ml of blood delivered to it Deprivation for more than 2 minutes results in cessation of activity myocardial hypoxia produces coronary artery vasodilation


Pathophysiology :Pathophysiology Coronary insufficiency energy demand exceeds the supply patients with coronary artery disease (CAD) may have a mix of ischemia and scarring Heart failure w/o myocardial depression Severe acute hypertension or sudden mitral regurgitation quickly leads to left ventricular pump failure without myocardial depression. This is termed afterload mismarch with limited preload reserve. This happens in a normal heart that is fully distended and unable to compensate by increasing its preload.


Pathophysiology :Pathophysiology Impaired cardiac filling chronic constrictive pericarditis Intrinsic myocardial pathology infiltrative, inflammatory, or tumor stages may influence myocardial contractility, and diseases, such as lymphoma, actually infiltrate into the myocardium distorts and interferes with normal myocardial contractility and eventually causes failure of the myocardial pump the result of a group of diseases called myocardiopathies in which there is destruction of the functional myocardial cells.


Pathophysiology :Pathophysiology Intrinsic myocardial pathology cardiac reserve change in heart rate - above certain limits, such as a rate of 170 to 180 beats/min in young people or 140 in older people, cardiac output begins to decline ejection fraction (50-60%), difference between the left ventricular stroke volume and the end-diastolic volume increased contractility increases EF decrease in EF early evidence of ventricular failure redistribution of cardiac output shift of blood from reservoirs to the heart


Volumes :Volumes End-diastolic volume (EDV) Stroke volume Cardiac output End-systolic volume (ESV) Ejection fraction (EF)


Wall motion :Wall motion Normal Hypokinetic Akinetic Dyskinetic


Noninvasive Nuclear Cardiology Procedures :Noninvasive Nuclear Cardiology Procedures 33 - 50 % of nuclear procedures


Myocardial Perfusion Imaging :Myocardial Perfusion Imaging


Myocardial Perfusion Imaging :Myocardial Perfusion Imaging Determine the adequacy of blood flow to the myocardium Detection and evaluation of coronary artery disease (CAD) May be performed with: 201Tl 99mTc Positron emitters


Myocardial Perfusion Imaging :Myocardial Perfusion Imaging Diagnosis of obstructive coronary disease – detection of relatively decreased myocardial perfusion distal to the site of vasculare obstruction Rest vs. Stress Increased oxygen demand is met by increased coronary blood flow Stenosed artery perfusion is increased less than neighboring tissue


Myocardial Perfusion Imaging :Myocardial Perfusion Imaging May not be abnormal with 90% stenosis at rest 50 % or more stenosis detected with myocardial perfusion imaging with stress Comparison of rest/stress is the same regardless of radiopharmaceutical


Choice of Radiopharmaceutical :Choice of Radiopharmaceutical Radiopharmaceutical Fixed Washes out Redistributes


Choice of Radiopharmaceutical :Choice of Radiopharmaceutical


Thallium Exercise – Redistribution Imaging :Thallium Exercise – Redistribution Imaging


Biokinetics of 201Tl :Biokinetics of 201Tl Similar to potassium Crosses cell membrane by active transport mechanisms Adenosine triphosphate (ATP)-dependent Na+ - K+ pump Localization phases Initial distribution based on blood flow and cellular extraction by viable myocardium Delayed redistribution or equilibrium based on continued extraction and ongoing washout of previously extracted thallium


Biokinetics of 201Tl :Biokinetics of 201Tl 90% extraction efficiency 3% - 5% of the total injected dose is localized in the heart Thallium clearance occurs mostly by urinary excretion Effective half-life of about 55 hours


Thallium Imaging :Thallium Imaging SPECT standard protocol Planar used under extraordinary circustances Reduced sensitivity SPECT good in detection of single-vessel disease especially LCX and multivessel involvement 85% sensitivity with SPECT


Technique :Technique Initial postexercise images Delayed (redistribution) images Quality control important Patient Preparation NPO 4 – 6 hours (decrease uptake in bowel and liver) Calcium-channel blockers and B blockers (propranolol) should be discontinued (interfere with obtaining adequate stress by limiting heart rate Long-acting nitrates should be withheld on the day of testing


Technique :Technique Exercise Protocol Multistage treadmill exercise test based on Bruce or modified Bruce protocol Bicycle ergometer (usually results in less optimal exertion) Pharmacologic (covered later) 2 mCi is injected at peak stress, with the patient continuing to exercise for 30 sec to one minute


Technique :Technique


Technique :Technique


Technique :Technique Exercise Protocol Maximum Stress Chest pain ECG changes 85% predicted maximum heart rate (220 beats/min minus the patient’s age in years) Heat rate – blood pressure product exceeds 25,000 (max heart rate multiplied by max systolic blood pressure)


Technique :Technique Exercise Protocol Most common false-negative and reduced test sensitivity is due to failure of the patient to achieve maximal stress


Technique :Technique Initial Postexercise Imaging Redistribution begins immediately Imaging should begin within 10 – 15 min postexercise Upward creep Patient positioning Left arm Breast compression ? ? 1800 SPECT (45-degree RAO to 45-degree LPO; 64X64; 64 stop; total study time: 30 min) Single vs. multidetector


Technique :Technique


Technique :Technique


Technique :Technique Initial Postexercise Imaging Post-imaging instructions Eat Avoid strenuous exercise If stress images are normal some labs stop here, others perform redistribution study


Technique :Technique Redistribution Imaging 3 – 4 hours after initial set Same camera and settings 1 mCi 201Tl is administered before reimaging (immediately to 1 hour before reimaging); to ensure adequate ambient thallium is available for redistribution 24 hr repeat images can be obtained in patients who exhibit nonreversible defects on the 4-hour images


Technique :Technique


Technique :Technique Image Processing SPECT reconstruction Short axis (SA) Vertical long axis (VLA) Horizontal long axis (HLA) (diagram follows) 1 – 2 pixels in thickness Background subtraction Contrast enhancement Image filtering


Technique :Technique


Image Display :Image Display Resting vs Stress Image Sets Orientation standardization Bull’s eye or polar map


Image Display :Image Display Polar Map View of heart from apex opened up like an umbrella Perfusion defects at base tend to be overemphasized Perfusion defects at apex tend to be under-represented Quantitative comparison with “normals” file


Interpretation :Interpretation Alignment of rest/stress Sinogram – quality control Soft tissue attenuation – Breasts – anterior or lateral wall defects Left hemidiaphragmatic elevation – inferior wall Typical apex thinning, base of intraventricular septum and inferior wall See table 8-3


Abnormal Scan :Abnormal Scan See list on page 143 Reversible defects Nonreversible (fixed) defects Rapid washout or reverse redistribution not well defined Defects usually seen on two or more projections Chronically ischemic, “hibernating” myocardium Remains poorly perfused at rest Allow additional time for redistribution or reinjection (1 – 2 mCi) Eating between images may alter Na – K pump, resulting in less reversibility


Abnormal Scan :Abnormal Scan Reverse Redistribution Defect on delay Mechanisms uncertain Associated with prior MI, especially after revasculariation or thrombolytic therapy Lung activity Can be quantified Transient left ventricular dysfunction Correlates with multivessel coronary artery disease Correlates with increased morbidity and mortality


Technetium and Myocardial Perfusion :Technetium and Myocardial Perfusion Long retention in the myocarduim Very little redistribution Lipophilic agents enter cells by passive diffusion Localization still proportional to regional blood flow Cardiolite/Myoview Sestamibi/Tetrofosmin (some say better clearance with tetrofosmin) Postexercise hepatic activity is increased if submax stress Meal or no-meal Cold water


Technetium and Myocardial Perfusion :Technetium and Myocardial Perfusion Separate injections for rest/stress One-day or two-day protocols Thallium/Technetium imaging protocol (dual-isotope) 201Tl: 2.5 – 3 mCi 99mTcMIBI: 20 – 30 mCi


Technetium and Myocardial Perfusion :Technetium and Myocardial Perfusion


Technetium and Myocardial Perfusion :Technetium and Myocardial Perfusion


Gated SPECT :Gated SPECT EKG Gate Wall motion Wall “thickening” 8 to 16 frames Fixed defect evaluation (breast/diaphragmatic attenutation) Myocardial viability Resting defects classified as viable if wall motion can be confirmed.


Pharmacologic Stress :Pharmacologic Stress B blockers, calcium-channel blockers, LBBB may produce exercise-induced septal perfusion defects Pharmacologic stress may be answer Sensitivity and specificity comparabel to maximal exercise Non-nitrate vasodilators Dipyridamole (Persnatine Adenosine Inotropic drug dobutamine


Pharmacologic Stress :Pharmacologic Stress Should not be used on patients with unstable angina, acute myocardial infarction (within 72 hours), hypotension or refractive congestive heart failure. Dipyridomole and adenosine may exacerbate or induce bronchospasm, should not be used in patients with asthma or significant COPD


Dipyridomole :Dipyridomole Adenosine deaminase inhibitor Produces selective vasodilation of coronary arteries Increases blood flow by 3 – 5 times (1 – 3 with exercise) May cause angina, head-aches, dizziness, flushing and nausea Aminophylline can be used as antagonist


Dipyridomole :Dipyridomole Xanthine containing meds (theophylline) withheld for 48 hours) Caffeine withheld for 12 to 24 hours IV administration performed over 4 min (0.5 mg/kg in 20 – 40 ml; 0.142 mg/kg/min; total dose of 0.56 mg/kg) Myocardial perfusion agent administered 3 – 4 min. after dipyridomole or 7 – 8 min into the study


Adenosine :Adenosine 140 ug/kg/min for 6 min Dose may be titrated downward for unstable patients Myocardial perfusion agent is injected at a 3 min. into the adenosine infusion Dipyridamole should be withheld for 12 to 24 hr Side effects in 75% of patients Flushing, shortness of breath, chest pain Atrioventricular block; 1st degree and 2nd degree block Biologic half-life – less than 10 seconds


Dobutamine :Dobutamine Increases myocardial oxygen demand through increases in heart rate and contractility In response normal coronary arteries dilated to increase blood flow Increased blood flow is 3X baseline Protocol consists of gradually increasing infusion Beginning with 5-10 ug/kg/min for 3 min Increasing every 3 min until max dose of 40 ug/kg/min Myocardial perfusion agent is injected 1 min after beginning the highes dose and infusion maintained for additional 2 min


Dobutamine :Dobutamine Alternative for patients with asthma or COPD or patients who have had caffine or methylxanthine medications within 12 hrs or for those taking oral dipyridamole Side effects – dimilare to adenosine including palpitation, chest pain, flushing, headache and dyspnea PVC’s, ventricular tachycardia, and atrial fibrillation may occur Biologic half-life: 2 min B blocker may be used as antagonist


Clinical Applications :Clinical Applications CAD Hemodynamic significance of coronary stenosis Collateral coronary vessels Evaluation of revascularization Risk stratification in CAD (patients with known CAD and normal stress MPI, yearly rate of MI or death of less than 1%) Risk stratification after MI Myocardial Viability Evaluation of acute chest pain (see text)


Definitions :Definitions Review definitions - page 376 in text


First-Pass Radionuclide Angiography(RNA) :First-Pass Radionuclide Angiography(RNA)


Purpose :Purpose Advantages acquisition times are short the data represent one isolated physiologic or pathophysiologic state 99mTc agents allow for peak exercise study followed by perfusion imaging excellent atrioventricular separation right ventrical EF


Purpose :Purpose Disadvantages separate injections for each view need to position patients carefully quality of injection bolus data processing


Indications :Indications Coronary artery disease (CAD) Valvular heart disease Congenital heart disease


Technical and Procedural Aspects :Technical and Procedural Aspects Radionuclide 99mTcDTPA - enhanced excretion can use other 99mTc agents MIBI PYP Myoview RBC Electrocardiogram assess cardiac rhythm to avoid injecting patient unnecessarily


Technical and Procedural Aspects :Technical and Procedural Aspects Radionuclide administration preferable and external jugular volume should not exceed 1 to 1 1/2 ml bolus should be rushed in with 10 - 20 ml of saline 0.3 to 0.4 mCi/kg Instrumentation 150k to 200k cps computer high temporal and spatial resolution


Technical and Procedural Aspects :Technical and Procedural Aspects Patient orientation and positioning test injection (.5mCi) to find position most informative and widely used views 20o to 30o right anterior oblique anterior use marker for motion on treadmill studies Post-acquisition procedure view data reframe at 1-sec interval helps in assessment


Technical and Procedural Aspects :Technical and Procedural Aspects Data Processing generate a time-activity curve from a region of interest around the ventricle, creating a representative cycle from as many usable beats in the time-activity curve as possible correct representative cycle for background activity then the ejection fraction is determined the cycle can then be viewed in cine format for analysis of wall motion generate a pulmonary time-activity curve.


Interpretation :Interpretation Inspection of transit through the central circulation left-to-right shunt quality of bolus tracer transit through right and left heart Inspect for problems such as high background, arrhythmia's and patient motion Left ventricular ejection fraction should be 0.50 to 0.80 and wall motion symmetric


Interpretation :Interpretation Response to exercise for a patient with CAD is a decrease in EF The more extensive the disease the lower the exercise EF Regional-wall-Motion abnormalities are more specific for coronary disease


Equilibrium Gated Radionuclide Ventriculogram :Equilibrium Gated Radionuclide Ventriculogram MUGA


Purpose :Purpose Examine the function of the pumping chambers of the heart Left ventricle measurements are more accurate than the right because of the heart’s anatomy (gated first-pass study with radionuclides that do not pass the lungs maybe used for the right ventricle)


Radiopharmaceutical Preparations :Radiopharmaceutical Preparations Labeled albumin particles leak from blood pool faster than RBC’s RBC’s In-Vivo label In-Vitro label Dose Resting: 15 - 20 mCi Stress: 30 mCi


Acquisition :Acquisition Electrocardiogram is used as a triggering device (gate) for frame by frame acquisition Hundreds of cardiac cycles are averaged in to composites Images may be displayed in a cine loop to simulate a beating heart Most useful image is obtained in a “best septal” projection, 30 40o LAO with slight caudal tilt (camera distance should be considered)(LVEF)


Acquisition :Acquisition Other views to examine wall motion RAO Anterior Steep LAO or Left Lateral LPO High-resolution/low-sensitivity collimator can be counterproductive


Acquisition :Acquisition Matrix size of 64 X 64 is usually acceptable 32 X 32 is too coarse Frames per R-to-R is variable (150 - 200K cts/fr) more frames better temporal resolution but longer acquisition time for the same statistics less than 14 frames introduces errors 16 frames give accurate systolic information 24 frames give smoother cine display and better temporal resolution


Acquisition :Acquisition Forward gating first frame begins with the R wave data is acquired in following frames for the preselected number of frames or until the next R wave. if the rate is regular the end of the last frame will coincide with the next R wave if rate is irregular some data in the last few frames maybe lost causing a “flickering” on cine display


Acquisition :Acquisition “Flickering” can be reduced by retrospective gating data is stored in buffers for the complete cycle and then transferred to frames with different time-per-frame Standardize acquisition and processing PVC or irregular beats may be excluded by “bad-beat” rejection software detection of R-to-R intervals outside of a given tolerance from the predicted (usually 10%)


Acquisition :Acquisition “bad-beat” software may hold data in a buffer and compare the cycle length to a “window” of averaged cycle times Special arrhythmia is bigeminy two different heart rates alternate regularly may use separate acquisition windows and calculate LVEF for each rate


Processing :Processing Temporal and Spatial filtering is usually performed before display of the images in cine mode Ejection Fraction outline of edges of the LV is critical manual auto-edge detection percent of peak counts second derivative (inflection point) Fourier transform


Processing :Processing Ejection Fraction background should be subtracted do not draw region over aorta or other large blood pools LVEF = volume curve (frame-activity curve) regional ejection fractions (LVED cts - Bkg) - (LVES cts -Bkg) (LVED cts -Bkg)


Processing :Processing Other processing isovolumic relaxation period time to peak filling peak filling rate first third filling fraction stroke volume paradox images first harmonic Fourier phase and amplitude analysis minimum/maximum images


Volume Measurements :Volume Measurements Determine LVEDV LV volume = calculation of LV count rate varies (Blood-sample volume) X (LV count rate) (Blood-sample count rate)


Exercise EGRV (MUGA) :Exercise EGRV (MUGA) Bicycle ergometer 16 frame, 3 minute acquisitions Starting at rest and increasing levels of exercise at about every 3 1/2 minutes 3 min acquisition after 30 sec equilibration period Some do a post-exercise study EF at each stage


Interpretation :Interpretation Heart rate EF normal - 55% - 75%, average 65% low EF usually indicates prior infarctions increased LVEDV and heart rate will compensate in some cases EF and HR should increase with exercise


Interpretation :Interpretation Wall motion normal: converging vigorously on the center of the blood pool during systole hypokinetic: not moving enough akinetic: not moving at all dyskinetic: moving the wrong way


Myocardial Imaging :Myocardial Imaging


Anatomy :Anatomy Normal position - left of midline in the mediastinum, with apex angled forward and to the left Image sections, transverse, coronal, or sagittal will slice the heart obliquely Images must be realigned to the short or long axis of the heart


Anatomy :Anatomy Universal system of nomenclature Short axis (transverse or coronal) Vertical long axis (sagittal) Horizontal long axis (coronal or transverse) See description, page 407


Purpose :Purpose Functional imaging directly reflects the delivery of blood or perfusion to the myocardial tissue Provides physiologic information to compare with anatomical coronary artery angiography information in order to estimate coronary artery stenosis Helps determine myocardial viability Ischemia vs. infarction


Infarct -Avid :Infarct -Avid 99mTcPYP Avidity of PYP for hydroxyapatite matrix of bone is primary mechanism for concentration in irreversibly damaged myocardial cells where there is an influx of calcium into the dying cells with active formation of various calcium-phosphate complexes.


Infarct -Avid :Infarct -Avid Planar imaging is performed 3 – 4 hours post injection of 10 – 20 mCi May perform SPECT Positive scan – 12 hours post acute infarction in most patients May become increasingly positive until about 72 hours Sensitivity greatest between 24 and 72 hrs


Infarct -Avid :Infarct -Avid Scan interpretation Abnormal scan – focal or deffuse uptake Abnormality graded according to intensity relative to activity in ribs or sternum