Advanced Cardiac Packet-compressed 2 PDF

# 20 Advanced Nuclear Cardiology ## Amy Brady and Krystle Glasgow Nuclear cardiology has become a major component of nuclear medicine. Many technologists are focused solely on performing cardiac studies. This chapter focuses on topics such as cardiac shunts, methyl iodobenzylguanidine (MIBG) imag...

# 20 Advanced Nuclear Cardiology ## Amy Brady and Krystle Glasgow Nuclear cardiology has become a major component of nuclear medicine. Many technologists are focused solely on performing cardiac studies. This chapter focuses on topics such as cardiac shunts, methyl iodobenzylguanidine (MIBG) imaging, β-methyl-p-(I-123)-iodophenyl-pentadecanoic (123I-BMIPP) imaging, ECG interpretation, and building an enhanced knowledge from where previous chapters book have left off. Board-certified nuclear medicine technologists who have had at least two years of full-time experience in nuclear medicine, and have fulfilled a few additional requirements, may be eligible to sit for the nuclear cardiology specialty board exam. Information regarding this specialty exam, such as the application and a content outline, can be found on the Nuclear Medicine Technology Certification Board website (http://www.nmtcb.org) under the Specialty Exams tab. Before taking the exam, it is essential to review topics such as instrumentation, quality control, patient care, the cardiovascular system, pathology, electrocardiogram (ECG), emergency care, radiopharmaceuticals, and interventional drugs. The Society of Nuclear Medicine and Molecular Imaging's website (http://www.snmmi.org) and American Society of Nuclear Cardiology's website (http://www.asnc.org) are great resources for approved cardiac imaging and stress procedures. Another excellent resource for preparing for this exam is the Nuclear Cardiology Technology Study Guide, which is available at the Society of Nuclear Medicine website. ## Equipment Equipment is a necessary component in nuclear cardiology and should be properly chosen for the specific purpose of its use. Once the equipment has been chosen, it is essential to have and maintain a first-class quality assurance (QA) plan for the equipment to produce high-quality imaging. ### Planar Imaging While planar imaging is no longer the standard approach used for myocardial perfusion imaging, it can be a great alternative for patients who are unable to have single-photon emission computed tomography (SPECT) imaging due to body habitus or an inability to remain in the position needed for SPECT imaging. For cardiac imaging, a small field of view scintillation camera is practical. When using the 10 in. field of view (FOV) with a matrix of 128 x 128, the result is about 2 mm of pixel spacing. A 15 in. FOV camera should be zoomed using a magnification of 1.2-1.5 so the pixel size is close to 2 mm. Energy windows around the photopeak should always be symmetric. The energy peak and window settings are camera-specific and should be established for each individual camera. In general, a 20% window is standard when using 99mTc. For 201Tl, a 30% window around the 70 keV peak and a 15% window around the 167 keV peak are sufficient. As far as collimation, it is recommended that a parallel-hole collimator be used for planar imaging. When using 99mTc, the low-energy, high-resolution collimator is usually best. When using 201Tl, a low-energy, medium-resolution (all-purpose) collimator is best since the counting statistics become limited with a high-resolution collimator. ### SPECT Imaging SPECT imaging cameras incorporate many variables that dictate their performance. Single-head cameras are widely used; however, the benefit of adding additional detectors is evident. Each detector added to a system doubles the acquired counts, which in turn, reduce the acquisition time. Another variable in SPECT imaging is the orbit of the detector. A more-traditional orbit used has been circular with step-and-shoot motion using a rotational range of 180° or 360 ° . When a `180°` orbit is recommended for SPECT imaging, having two detectors separated by `90°` as they rotate around the heart is the ideal method. When a `360°` orbit is used, having three detectors separated by `120°` from each other is also preferred. A more-modern orbit used in most SPECT imaging systems today is the elliptical or noncircular orbit. The elliptical reduces the distance from the camera to the body by following the body contour, which in turn improves spatial resolution. The combination of both SPECT and computed tomography (CT) adds a range of potential and integration. The SPECT apparatus usually contains a large FOV and dual detectors. The CT apparatus includes non-diagnostic units that are used for anatomical location and attenuation correction only. The CT apparatus may even include multi-slice units, which can perform stand-alone diagnostic scans ### Positron Emission Tomography Imaging Most dedicated positron emission tomography (PET) cameras consist of rings of small detectors. Four commonly used crystal types include bismuth germinate (BGO), gadolinium oxyorthosilicate (GSO), lutetium oxyorthosilicate (LSO), and lutetium yttrium orthosilicate (LYSO). PET scanners rely mainly on CT scans for attenuation correction, but can also use rotating-rod sources of germanium-68/gallium-68. The rotating-rod sources produce a transmission scan before or after the emission scan. The rotating-rod sources add approximately 3-8 min of scan time. ## Quality Contrast Quality control is the portion of quality assurance in which tests are performed to identify equipment problems and should be completed before acquiring patient studies. Organizations such as the American College of Radiology (ACR) and Intersocietal Accreditation Commission (IAC) require proof of a nuclear cardiology facility's performance of quality control. A quality control plan must be established for planar imaging, SPECT imaging, sealed-source Single Photon Emission Computed Tomography/Transmission Computed Tomography (SPECT/TCT) systems, x-ray-based SPECT/CT systems, dedicated PET imaging, and PET/CT imaging. The first step in creating a quality control plan for a nuclear cardiology facility is acceptance testing. Acceptance testing is completed once upon equipment installment and again upon any major upgrades It is recommended that the equipment perform as specified by the manufacturer according to National Electrical Manufacturers Association (NEMA) guidelines. The next step in creating a well-designed quality control plan is to establish routine checks that can be closely monitored to note changes in performance parameters. ### Planar Imaging Quality Control Planar imaging includes four quality control tests: energy peaking, uniformity test, resolution and linearity test, and a sensitivity test. * Energy peaking is used to confirm that the camera is counting photons having the correct energy * Uniformity is used to confirm that the camera's sensitivity response is uniform-consistent across the detector's face. Manufacturers may suggest whether uniformity be completed intrinsically or extrinsically. If uniformity is performed intrinsically, the radioactive point source should be positioned at a distance at least five times the crystal's useful field of view (UFOV). * Resolution and linearity tests are performed to check the camera's spatial resolution and its change over time, along with the detector's ability to image straight lines. ### SPECT Imaging Quality Control SPECT imaging includes all of the general quality control tests required for planar images plus a center of rotation (COR), high-count extrinsic flood-field uniformity correction, and Jaszczak SPECT phantom test. * The **COR** is a measure performed to ensure that the center field of view of the camera detector matches the software of the computer. A `99mTc` source can be used to perform the COR test on each detector head. COR testing should be performed in all detector formats if images are acquired in detector formations other than 180 ° . The accuracy of the COR alignment should be performed weekly and new COR calibrations should be performed after the camera is serviced, following power surges or outages, and for the computer after upgrades in the software. * An error in the COR can reduce spatial resolution and image contrast by blurring the image. An error can also cause significant artifacts in the image concerning the apex of the heart. A high-count extrinsic flood-field uniformity correction should be performed as directed by the manufacturer. The high-count flood is used to ensure that the efficiency of photon detection is constant across the surface of the collimated detector. It is recommended that 30-100 million count images be acquired for each detector, and a deficiency in the flood can lead to characteristic "ring" artifacts in SPECT imaging. * A Jaszczak SPECT phantom test is used to determine the 3D contrast, resolution, and uniformity of the camera. NEMA recommends that the 30 million count acquisition and section reconstruction using a Jaszczak SPECT phantom be completed quarterly. ### Sealed-source SPECT/CT Systems Quality Control Sealed-source SPECT/CT systems include all of the SPECT imaging quality control tests plus energy peaking, transmission source mechanics, and source strength. * Energy peaking is completed to confirm that the camera is counting photons in the proper energy windows. A check of transmission source mechanics is performed to confirm the operation of the source shutter and translating mechanics, and a reference "blank" transmission scan should be acquired. It is recommended that the transmission source mechanics scan is performed weekly and possibly daily. * The source strength is performed on systems using a gadolinium-153 (`153Gd`) transmission source to evaluate the transmission-to-cross-talk ratio (TCR) value. Source strength should be performed at least monthly, along with a baseline scan when the transmission source is installed or replaced. ### X-Ray-based SPECT/CT Systems Quality Control X-ray-based SPECT/CT systems include all of the SPECT imaging quality control tests plus additional quality control specific to CT imaging. The CT imaging quality controls include calibration and field uniformity. Calibration is performed with a special phantom, which includes inserts of known CT numbers. A CT imaging system is considered not calibrated when the error is greater than 5 Hounsfield units. Field uniformity is performed to ensure a uniform response throughout the FOV. ### Combined SPECT/CT Quality Control Combined SPECT/CT systems include all of the SPECT imaging and CT imaging quality control tests. However, when the SPECT/CT system is combined, the CT portion must additionally perform registration, attenuation correction accuracy, and mis-registration consequences. ### Dedicated PET Imaging Quality Control Suggested quality controls for PET imaging includes acceptance testing, sensitivity, transverse resolution, scatter fraction, accuracy of attenuation correction, and any other test recommended by the manufacturer. Sensitivity is performed to monitor sensitivity changes and proper operation of the scanner. It is recommended that sensitivity be performed daily or at least weekly. Transverse resolution is performed using a point source or rod source. It is recommended that transverse resolution be performed annually. It is also recommended that scatter fraction and accuracy of attenuation correction be performed annually. ### PET/CT Imaging Quality Control The quality control of the **PET** portion of PET/CT includes all of the suggested quality controls for PET imaging. The quality control of the **CT** portion of PET/CT also includes calibration and field uniformity. ### Combined PET/CT Quality Control Quality control for combined PET/CT systems includes the individual PET and CT portions as mentioned and also registration and attenuation correction accuracy. ### Radionuclide PET/CT Generator Radionuclide generators provide a convenient source of short-lived radionuclides. In a radionuclide generator, a longer-lived radionuclide, called the parent, decays to a shorter-lived radionuclide, called the daughter. The daughter can be removed periodically since it is replenished by decay of the parent. An example of parent-daughter systems used in radionuclide PET/CT generators is strontium-82 (`82Sr`)/rubidium-82 (`82Rb`). These systems have been developed commercially and are supplied as sterile, shielded, automatically operated devices. ## Dynamic Cardiac Imaging Dynamic cardiac imaging is beneficial when evaluating the heart's ability to function (especially in patients with a known cardiac disease). Indications for dynamic cardiac imaging are shown in the table below. | Indication | Description | | :-------------------------------------------- | :----------------------------------------------------------------------------------------------------------- | | Assess either left or right ventricular ejection fraction (EF) at rest and/or during exercise. | | | Evaluate regional wall-motion abnormalities, such as hypokinesia, akinesia, and dyskinesia (aneurysm), during rest or during exercise. | | | Evaluate ventricular function (EF and wall motion): | | | * before cardiac catheterization | | | * after a myocardial infarction | | | * in patients with valvular disease | | | * to monitor patients on doxorubicin and related chemotherapy agents | | | Estimate cardiac output, ventricular volumes, and other cardiac functional parameters. | | | Assess diastolic function of the left ventricle, such as peak-filling rate and time to peak-filling rate. | | | Evaluate and quantify left-to-right or right-to-left cardiac shunts. | | Dynamic cardiac imaging can be performed by the first-pass radionuclide angiography study and/or by the equilibrium radionuclide angiogram (ERNA) study. See figure 20.6 for examples of kinesis, hypokinesis, akinesis, and dyskinesis. ## First-Pass Radionuclide Angiography Study A first-pass study looks at both left and right ventricular function either at rest or stress The first-pass study also evaluates cardiac shunts, which refer to the movement of blood across the septum. Shunts are usually a congenital defect that typically close as the patient matures and can be either right-to-left or left-to-right. If surgery is needed, a first-pass study can verify resolution of the shunting after repair or calculate the amount of residual shunting if the repair is not complete. ### Acquisition Protocols when Assessing Left and Right Ventricular Function Radionuclides commonly used when determining either left or right ventricular function in first-pass studies include `99mTc-diethylamine triamine pentaacetic acid (DTPA)`, `99mTc-pertechnetate`, `99mTc-sestamibi`, and `99mTc-tetrofosmin`. A standard dose of `25 mCi (925MBq)` is commonly used for both rest and exercise studies; however, lower doses may be adequate. A bolus injection of the radionuclide should be pushed through a three-way stopcock connected to an intravenous catheter that has been placed in the antecubital or external jugular veins. Note that the radionuclide bolus should be pushed rapidly over `2-3 sec` when assessing left ventrical (LV) function such that the full width at half maximum (FWHM) of the bolus is less than 1 sec. A time-activity curve of the frames can be used to show the bolus flowing through the superior vena cava and determine the integrity of the bolus. If a bolus is fragmented and/or the FWHM is greater than 1 sec, then the study should be repeated. For right ventrical (RV) function, the radionuclide bolus should be pushed slightly slower over `3-4 sec` to achieve a FWHM of `2-3 sec` for the superior vena cava curve. For both LV and RV function, the radionuclide injection is followed by a `10-20 mL` saline flush. When being imaged for a first-pass study, the patient can be lying supine or sitting upright. A common imaging position used for LV function is the upright, straight anterior view With this view, overlap of anatomic structures may occur. To eliminate this overlap, a right anterior oblique (RAO) can be used When evaluating EF of the right ventricle, a shallow RAO is recommended to eliminate overlapping anatomic structures such as the left ventricle. The camera should be positioned as close to the patient's chest as possible to optimize resolution and maximize count-rate detection. The heart must be centered in the field of view. ### Processing and Results When Assessing Left and Right Ventricular Function Processing in nuclear cardiology has become more and more automated and faster over the years. With new technology and software, the technologist should still be observant when processing to ensure accurate results. Processing a first-pass study involves the creation of the initial time-activity curve (TAC), beat selection, creation of the initial representative cycle, background correction, creation of final representative cycle, and possibly motion correction. To create the initial TAC, the technologist should draw an initial ventricular region of interest (ROI). For beat selection, the technologist must identify the first and last beats to include in the representative cycle. When correcting background, the lung frame method is preferred; however, the periventricular method is a standard in many single-head gamma cameras. Once complete, the background correction should be applied to the initial representative cycle. The frames displaying the end diastolic and end systolic should be viewed and modified as needed. A final ROI should be drawn. The EF of the left ventricle is calculated from the final background-corrected representative cycle: **% EF = [(end-diastolic counts - end-systolic counts) / end-diastolic counts] x 100** **% EF = [(net diastolic counts - net systolic counts)/net diastolic counts] x 100** The left ventricular ejection fraction (LVEF) has a normal accepted range of `50-80%` for a resting study. The LVEF under stress conditions for most normal individuals is `56%` or greater When using separate end-diastolic and end-systolic ROIs, the normal range for right ventricular ejection ranges from `40` to `65%` in a rest study. RVEF usually increases during exercise, but may actually decrease in patients with proximal right coronary artery lesions and/or pulmonary hypertension. ## Cardiac Shunts Cardiac shunts are most-often found as a congenital defect, which usually closes on its own as a patient matures. However, if the shunt does not close, surgery may be needed. Cardiac shunt evaluations are most-often performed on pediatric patients and, therefore, the radioactive dose should be adjusted accordingly. While a nuclear medicine shunt evaluation is useful, ultrasound, Doppler imaging, and a cardiac catheterization are most currently used for shunt evaluation and quantification. A right-to-left shunt occurs when a malformation allowing communication between the two sides of the heart is complicated by a lesion or condition that increases the right-sided pressure to greater than that of the left side. Blood that is shunted from the right side to the left bypasses the pulmonary arterial circulation and is prematurely returned to the systemic circulation without being oxygenated. Left untreated, a right-to-left shunt will cause cyanotic heart disease. A standard dose of `2-5 mCi (74-185 MBq)` of 99mTc-macroaggregated albumin (MAA) can be used to evaluate a right-to-left shunt in the first-pass study. If a shunt is detected, there will be a premature visualization of the aorta before the lungs. The right heart may seem enlarged when compared to the left heart. The percentage of right-to-left shunting can be approximated by comparing the total body counts and total lung count, which is a connection allowing blood to bypass the lungs in a developing fetus, does not close following birth. This shunt allows oxygenated blood from the left heart to flow back to the lungs. When imaging a first-pass study to evaluate a left-to-right shunt, a `10 to 15 mCi (370-555 MBq)` dose of any of the `99mTc` radiopharmaceuticals listed above is standard. Note that the FWHM of a good radionuclide bolus should be `3 sec` or less. The total amount of frames acquired should be `2,000` and a matrix size of `64 x 64` or `32 x 32` is appropriate to use. If the shunt is detected, blood will return prematurely to the pulmonary circulation. Evaluation of the pulmonary TAC from the first-pass study may also detect the shunt. A normal pulmonary TAC will have a single large peak that is followed by a small peak. An abnormal pulmonary TAC will show the initial peak of the TAC to have a bump on the downslope. To quantitate the left-to-right shunt, several methods such as the `C2/C₁` method, the area ratio method, and the gamma variate method can be used. An example of the `C2/C₁` method is given in figure 20.10. ## Equilibrium Radionuclide Angiography (ERNA) Study As previously mentioned in the Cardiovascular System chapter of this review book, many names have been given to gated blood pool imaging, and it is important to recognize and become familiar with all of the names. A planar ERNA is used to primarily determine LV function at rest and/or during exercise stress or pharmacologic intervention. Ventricular function includes evaluating wall motion, EF, and other parameters of systolic and diastolic function SPECT ERNA can also be used to determine both global and regional ventricular function at rest and/or during pharmacologic intervention. ### Acquisition Protocols The radionuclide used in ERNA studies is `99mTc`-labeled red blood cells. For resting studies, the standard dosage is approximately `20-25 mCi/70 kg (740-925 MBq/70 kg)` body weight. For exercise studies, the standard dosage is approximately `25-35 mCi/70 kg (925-1295 MBq/70 kg)`. The three techniques for labeling red blood cells include in vivo, in vitro, and modified in vivo/in vitro . Poor labeling of the red blood cells results in an accumulation of `99mTc`-free pertechnetate in the mucosa of the stomach and in the thyroid gland. Causes of poor labeling include certain medications such as heparin and when "old" `99mTc`-pertechnetate of low specific activity is used. When available for resting studies, it is best to use a parallel-hole collimator with high resolution and spatial resolution of approximately `8 to 10 mm`. When performing a time-limited stress study such as the bicycle exercise, the low-energy all-purpose (LEAP) collimator should be used. However, if performing both a rest and stress study, the same collimator should be used for both. In this case, the LEAP is recommended. A slant-hole collimator is best when performing a caudal tilt of `10° to 15°`. Most ERNA studies are performed using a matrix zoomed at `64 x 64`. The standard energy window is ±10% of the `140 keV`. While frame mode is standard, list-mode acquisition is a good option because it offers increased beat-length windowing flexibility. In general, the ERNA study gathers data from many consecutive cardiac cycles that are all overlapped. The cardiac cycle is divided into a predetermined number of frames or images that generally range from ``16` to `32`. When a patient is connected to a three-lead ECG to the camera, the computer will start to acquire data when it sees the R wave and the time of the acquisition will be redirected to frame 1. This process is called "gating" and will continue until the information count density has been acquired. The data from all the cardiac cycles are basically overlapped to form a composite or summary image of the heart. The normal R-R interval is first computed and a tolerance limit of ±10% is usually chosen. If the R-R interval is shorter than normal, the data will not be acquired into one of the latter frames. If the R-R interval is longer than normal, the data acquisition will pause and wait for the next R wave. ### Positioning The three main views needed when assessing the wall motion of the left ventricle are the LAO, anterior, and left lateral or posterior oblique The patient should be in the supine position or the right lateral decubitus position. The **45° LAO** view is used to visualize the septum. Depending on the patient, the `45°` angle may vary slightly. The orientation should be that the long axis of the ventricle is vertical with the apex pointing down and the left ventricle on the right side of the image. A caudal tilt of approximately `10° to 15°` can be used to help separate the atria from the ventricle. ### Image Display and Processing The multiple-view ERNA is usually displayed as an endless-loop simultaneously in zones of the computer screen. Use of a linear gray scale is recommended when the views are displayed. A smoothing process (or Gaussian 9-point smoothing) is used to remove statistical fluctuations from the image. To determine the EF, a LV volume curve must be generated from manually drawing the ROI over the end diastole and end systole. Background must also be taken into consideration. A ROI -5-10 mm away from the end-diastolic border and in the 2 o'clock to 5 o'clock area should be drawn to determine background. Once that is established, a background correction should be applied by simply subtracting background counts from LV ROI counts. The LVEF can then be determined by using the following equation: **LVEF = [(end-diastolic volume (EDV) - end-systolic volume (ESV))/EDV] x 100** Both a global and regional ejection fraction can be determined. The global EF is the entire ventricular volume. To evaluate regional EF, the ventricle must be divided into segments. The regional EF is helpful when evaluating regional wall motion. When assessing ventricular function with stress, the baseline ERNA images should be displayed side-by-side with the stress images, which help in determining changes. ## Myocardial Infarct-Avid Imaging, MIBG Imaging, and 123I - BMIPP Imaging While myocardial perfusion imaging is the most-routinely performed nuclear cardiac study, other infrequent cardiac studies provide beneficial information for patients with not only cardiovascular disease but other diseases that affect the heart and vascular system as well. Myocardial infarct-avid imaging, MIBG, and 123I-BMIPP studies are commonly used for such conditions. ### Myocardial Infarct-Avid Imaging Chest pain is one of the top reasons most people go to the emergency department. While most patients can be diagnosed with an acute myocardial infarction, few patients will have results that are indeterminate. For those patients, a myocardial infarct-avid test would be beneficial. This test uses radiopharmaceuticals `99mTc-PYP` and `111In-antimyosin`. (Note: In-antimyosin is not currently available.) When using `99mTc-PYP`, the window of maximum diagnostic yield is `48-72 hr` after the infarct. However, positive results can be seen as early as `12 hr` post-infarct. When using `¹¹¹In-antimyosin`, the window of maximum diagnostic yield is `18-24 hr` after the infarct. ### MIBG Imaging `123I-MIBG` is a sympathetic nerve imaging drug typically used to diagnose neuroendocrine tumors. However, developments in cardiac imaging have led to the ability to detect abnormalities in patients with heart failure using `123I-MIBG`. Patients with heart failure have a decreased ability for norepinephrine synthesis, storage, and release. This decreased ability results in an increase and higher concentration of circulating norepinephrine that is stored in granules in the presynaptic nerve terminals, which causes chronic stimulation. `MIBG` is thought to localize to myocardial sympathetic nerves due to its structural similarity to norepinephrine and uptake in the catecholamine storage granules, which reflect the extent of sympathetic innervation in the myocardium. Therefore, uptake of `123I-MIBG` is usually associated with diseases that result in heart failure or possibly fatal ventricular arrhythmias. A typical dose of `10.0 mCi (370 MBq) 123I-MIBG` is given intravenously and planar images of the anterior chest are obtained at both `10 min` and `4 hr` post-injection. SPECT images may also be useful. A radius of `180°`, RAO to LAO, should be used with a minimum of `60` stops at `30 sec` per stop. A `64 x 64` matrix should be used. Uptake of `123I-MIBG` is measured by defining the heart-to-mediastinum uptake ratio and assessing the washout rate over time. Heart failure patients have a low heart-to-mediastinum ratio and high or increased washout. ### 123I-BMIPP Imaging `123I-BMIPP` is used as an "ischemic memory tracer" to identify significant ischemia in patients with coronary artery disease (CAD) by assessing fatty acid metabolism. An intravenous injection of `3-4 mCi 123I-BMIPP` is a typical protocol. A LEAP or LEHR collimator is recommended along with a ±20% energy window around the `159 keV` of `123I`. Planar images of the anterior chest are obtained `15-30 min` post-injection along with a `4 hr` delayed image. SPECT images may also be useful and a radius of `180°`, RAO to LAO, should be used with a minimum of `60` stops at `30 sec` per stop. A `64 x 64` matrix should be used. A positive `123I-BMIPP` study will be evident within `20-30 min` of the ischemic event and will stay positive for up to `2 weeks`. ## Emergency Care and ECG Interpretation All employees in a nuclear cardiology facility should have basic life support (BLS) cardiopulmonary resuscitation (CPR) training. When conducting exercise and pharmacologic stress testing, at least one technologist should be trained in advanced care life support (ACLS) CPR, as well as an available physician. ACLS is an extension of BLS designed for healthcare providers who participate directly or indirectly in the resuscitation of a patient. ACLS guidelines are published by the American Heart Association and were last updated in 2015 at the time of publication of this text. The current ACLS guidelines use algorithms that are a set of instructions presented in the form of a flowchart to standardize treatment and increase effectiveness. Knowledge of pharmacology along with ECG interpretation is essential in ACLS training. ECG interpretation is an invaluable skill used in nuclear cardiology. In 1903, Willem Einthoven invented the first electrocardiogram machine. Today, there are many ECG monitors on the market, but they all record electrical conduction through the heart. Electrodes are used to detect the electrical activity generated by the myocardial cells. The ECG monitor has one positive electrode, one negative electrode, and one ground electrode. Special ECG paper is used to print out heart rhythms and measure particular events such as the heart rate. The paper is marked off in a grid on which each small square is 1 mm in length and represents 0.04 seconds. The larger square is 5 mm in length and represents 0.20 seconds. When interpreting an ECG, it is important to become very familiar with what is normal. It is also important to evaluate five vital items from an ECG: 1. **P wave** for size, shape, and location in the waveform. If the P wave precedes the QRS complex, the electrical impulse is being initiated by the sinoatrial (SA) node Absence of P waves or abnormality in their position relative to the QRS complex indicates that the pulse is starting outside the SA node and that an ectopic pacemaker is present. 2. **Atrial rhythm** and **determine the atrial rate** by measuring the P-P intervals and comparing. P waves should occur at regular intervals. Also, count the number of P waves in 30 large squares (or 6 seconds) and multiply by 10 to obtain the atrial beats per minute. 3. **PR interval** should be calculated. Simply count the number of small squares between the beginning of the P wave and the beginning of the QRS complex, then multiply by 0.04 sec. A normal PR interval is between 0.12 and 0.20 seconds or approximately 3-5 small squares. 4. **Ventricular rhythm** and **determine the ventricular rate** by measuring the R-R intervals and comparing. The R waves should occur at regular intervals. To find the ventricular rate, count the small squares between two R waves. Each small square equals 0.04 seconds; 1,500 squares equal 1 min. Divide 1,500 by the number of squares counted. Also check that the QRS complex is an appropriate shape for the particular lead used. 5. **Duration of the QRS complex** by counting the small squares between the beginning and end of the QRS complex and multiply by 0.04 seconds. A normal QRS complex is less than 0.12 seconds or three fine lines on the ECG paper. ## Stress Protocols and Radiopharmaceuticals Both exercise stress and pharmacologic stress tests are great protocols in the diagnosis of CAD. ### Exercise Stress Test Exercise is the preferred method for patients who are able to exercise and can reach at least 85% of the age-adjusted maximal predicted heart rate and five metabolic equivalents (METS). Exercise modalities include the treadmill or the upright bicycle. Although the treadmill is the most widely used, the bicycle is preferred when completing a dynamic first-pass study. Clinical indications and contraindications for the exercise stress test given by the ASNC are listed in the table below. | Clinical Indication | Description | | :--------------------------------------------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Detection of obstructive coronary artery disease in patients with: | | | * an intermediate pretest probability of CAD based on age, gender, and symptoms | | | * high-risk factors for CAD | | | Risk stratification of post-myocardial infarction patients before and after discharge | | | Risk stratification of patients with chronic stable CAD into a low-risk category that can be managed medically or a high-risk category that should be considered for coronary revascularization | | | Risk stratification of low-risk acute coronary syndrome patients and intermediate-risk acute coronary syndrome patients `1-3` days after presentation | | | Risk stratification before non-cardiac surgery in patients with known CAD or those with high-risk factors for CAD | | | To evaluate the efficacy of therapeutic interventions and in tracking subsequent risk on the basis of serial changes in myocardial perfusion in patients with known CAD | | In addition to providing information about exercise capability, an exercise stress test can be used to assess risk in patients with known or suspected CAD. The Duke Treadmill Score is a prediction of CAD in a patient with chest pain undergoing an exercise stress test. The calculation for the Duke Treadmill Score is given in the table below. | Clinical Indication | Description | | :--------------------------------------------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------- | | High-risk unstable angina | | | Decompensated or inadequately controlled congestive heart failure | | | Uncontrolled hypertension (blood pressure >200/110 mm Hg) | | | Uncontrolled cardiac arrhythmias | | | Severe symptomatic aortic stenosis | | | Acute pulmonary embolism | | | Acute myocarditis or pericarditis | | | Acute aortic dissection | | | Severe pulmonary hypertension | | | Acute myocardial infarction (<4 days) | | | Acutely ill for any reason | | | Known left main coronary artery stenosis | | | Moderate aortic stenosis | | | Hypertrophic obstructive cardiomyopathy or other forms of outflow tract obstruction | | | Significant tachyarrhythmias or bradyarrhythmias | | | High-degree atrioventricular (AV) block | | | Electrolyte abnormalities | | | Mental or physical impairment leading to inability to exercise adequately | | | If combined with imaging, patients with complete left bundle branch block (LBBB), permanent pacemakers, and ventricular pre-excitation (Wolff-Parkinson-White syndrome) should preferentially undergo pharmacologic vasodilator stress test (not dobutamine stress test) | | ### Procedure Patient preparations for an exercise stress test include nothing to eat for 2 hr before the test and possibly discontinuing certain blood pressure medications, depending on the referring physician. A patient who is scheduled later in the day should eat a light breakfast. An 18- to 20-gauge intravenous catheter should be inserted and secured before starting radiopharmaceutical injection during the exercise stress. The patient's electrocardiogram should be monitored continuously during the exercise test and into the recovery phase for at least 5 min or until the resting heart rate is <100 beats/min and/or any exercise-induced ST-