Stress echo workshop STRESSORS Adham Ahmed, MD Lecturer of Cardiology, Ain Shams Indications of Stress Echo CAD Diagnosis Prognosticat ion 1
Physiologic Basis 1930s: Tennant and Wiggers Relationship between systolic contraction and myocardial blood supply to the left ventricle Demonstrated rapid and predictable development of dyskinesis 3 Physiologic Basis Physiologic stress results in An increase in heart rate and Contractility HR and contractility maintained by an increase in myocardial blood flow 4 2
Physiologic Basis Increase in Systolic wall thickening Endocardial excursion Global contractility Leads to decrease in end-systolic volume Increase in ejection fraction May be blunted in advanced age, hypertension or in presence of beta blocker therapy 5 Physiologic Basis Presence of coronary artery stenosis Increased oxygen demand not adequately accommodated (supply-demand mismatch) Development of ischemic cascade 6 3
Ischemia Cascade The answer to the Question Why Echo Physiologic Basis Stressor elimination Myocardial oxygen demand is reduced and ischemia resolves Normalization may occur rapidly Typically recovery takes 1 to 2 minutes depending on severity of ischemia Stunned myocardium: functional abnormalities persist after transient ischemia for a longer period May last days or weeks 8 4
Stressors in Stress Testing 5
Methodologies Advantage: versatility Exercise Treadmill Supine bicycle Upright bicycle Handgrip Stair step Non-exercise Dobutamine Dipyridamole Adenosine Pacing 11 Treadmill Provides useful clinical information Exercise capacity Blood pressure response Arrhythmias Protocols: Bruce, Balke, Naughton, etc. 12 6
Treadmill Addition of echocardiography Not intended to alter exercise protocol Echocardiography images obtained pre- and postexercise Challenge of obtaining images immediately post exercise Ischemia may resolve quickly after exercise Must obtain images with 1 to 1.5 minutes 13 Protocol Patient is prepared for treadmill stress testing. Instructions provided on transition from the treadmill to the examination table after exercise. Resting echocardiographic images obtained, reviewed, and stored. Standard treadmill exercise examination performed. Patient moves as quickly as possible after exercise to the examination table. Post exercise imaging acquiring and recorded. Digital images reviewed, and representative loops selected. Digital images stored on permanent medium. 14 7
Bicycle Ergometry Stationary bicycle ergometry: first form of exercise in conjunction with echocardiography Currently: Availability of supine bicycle systems permit a variety of patient positions 15 Advantage: ability to image throughout exercise, particularly at peak stress Avoids potential problem of rapid recovery Allows onset of wall motion abnormality to be documented Wall motion abnormalities are more easily seen in peak exercise versus post exercise Image acquisition is less rushed lending itself to better quality images 8
Disadvantage Workload Bicycling in supine position may be uncomfortable for some patients Supine position appears to facilitate the induction of ischemia Perhaps by increasing venous return and preload. Associated with greater blood pressure response. Ischemia occurs at a lower heart rate during supine versus upright exercise. 17 Bicycle Ergometry Protocol Patient prepared for standard stress testing. Patient instructed how to perform bicycle exercise. Patient positioned on supine ergometer and secured in place. Rest images obtained (table inclined to optimize images). Exercise protocol begins at a workload of 25 W and a cadence of 60 rpm. Images monitored throughout exercise. At peak exercise, a full series of images is obtained. After cessation of exercise, wall motion is monitored to document resolution of induced ischemia. Representative images are selected and rearranged for digital storage. 18 9
Exercise Stress Testing Treadmill Bicycle Most potent Imaging at Peak Stress and during each stage of stress Can accurately measure the time of onset of ischemia Avoids problem of early resolution of ischemia Prognostically important Exercise as a Stressor Prototype of Demand driven ischemic stress Hyperventilation Hypercontractility of Normal Walls Drawbacks Excessive Tachycardia Circumvented by Pharmacological Stressers Excessive chest wall movement Unable to exercise at all or maximally 10
Methodologies Advantage: versatility Exercise Treadmill Supine bicycle Upright bicycle Handgrip Stair step Non-exercise Dobutamine Dipyridamole Adenosine Pacing 21 Dobutamine Stress Echocardiography Dobutamine: synthetic catecholamine causes Inotropic and chronotropic effects Affinity for ß 1 receptors in the myocardium and vasculature Cardiovascular effects are dose dependent Augmented contractility occurring at lower doses followed by a progressive chronotropic response at increasing doses Changes in vascular resistance (i.e. blood pressure) are unpredictable 22 11
Dobutamine Stress Echocardiography Distinction between exercise and Dobutamine Change in venous return is increased in exercise Autonomic nervous system-mediated changes in systemic and pulmonary vascular resistance are quite different Heart rate is less important with Dobutamine compared with exercise Ischemia may be induced even if target heart rate is not achieved due to greater augmentation of contraction Primary indication for Dobutamine as a substitute for exercise stress echocardiography Patients unwilling or unable to exercise adequately Detection of viable myocardium 23 Dobutamine Stress Echocardiography Atropine May be used in conjunction with Dobutamine to augment heart rate increases Patients on beta blockers 24 12
Protocol for Dobutamine Stress Echocardiography Patient preparation for stress testing IV access obtained Digital images obtained for baseline study Continuous EKG and BP monitoring Dobutamine infusion of 5 (or 10) µg/kg/min Infusion rate is increased every 3 minutes to doses of 10, 20, 30, and 40 µg/kg/min 25 EKG, Echocardiograms and BP are monitored continuously Low-dose images are acquired at 5 or 10 µg/kg/min (at first sign of increased contractility) [maybe obtained at smaller dose in severely impaired function] Atropine in aliquots of 0.5 to 1.0 mg can be given during the mid and high doses to augment the heart rate response Mid-dose images are acquired at either 20 or 30 µg/kg/min Peak images are acquired before termination of the infusion Post-stress images are recorded after return to baseline The patient is monitored until he or she returns to baseline status 13
End Points and Reasons to Terminate Dobutamine Infusion During Stress Testing Exceeding target heart rate of 85% agepredicted maximum Development of significant angina Recognition of a new wall motion abnormality Arrhythmias such as atrial fibrillation or non-sustained ventricular tachycardia Limiting side effects or symptoms 28 14
Diagnostic End Points Max dose of pharmacological agent Achievement of THR Akinesis of 2 LV segements Severe Chest pain Obvious ECG positivity 2mm ST shift Submaximal Nondiagnostic End Points Non tolerable symptoms Limiting Asymptomatic side effects Hypertention (BP > 220/120) Hypotension (BP drop > 40mm Hg) Supraventricular Arrythmias Complex Ventricular Arrythmias VT Frequent polymorphic VPC 15
Safety of Dobutamine Short-half life May be utilized in patients with bronchospastic disease Common side effects Minor arrhythmias Palpitations or anxiety 31 Dipyridamole and Adenosine Potent vasodilators Adenosine: short-acting direct coronary vasodilator Dipyridamole: slower acting. Inhibits adenosine uptake Adenosine and dipyridamole generally cause changes less significant and shorter lived than Dobutamine Used in nuclear imaging studies more often than echocardiography 32 16
Dipyridamol Stress Echo Protocol 17
Ergonovine Stress Protocol for Coronary Vasospasm Choosing Among the Different Stress Modalities 36 18
Situations where Pharmacological Stress is preferred to Exercise Stress Stressing Agents Stressor Pro Con Treadmill Physiologic, simple, less expensive, good for patient who can walk Dobutamine No exercise needed Caution in patients with arrhythmias Adenosine or dipyridamole (used with nuclear) No exercise needed; uncomfortable sensation of heart stoppage Adenosine may induce bronchospasm caution in COPD and asthma! 19
Dipyridamol Stress Preferred Hypertension Atrial and Ventricular Arrhythmias Dobutamine Stress Preferred Conduction disturbances Bronchospastic diseases On Xanthine medications Caffeine containing drinks Tea Coffee Cola 20
More myocardial dysfunction Less blood flow heterogeneity Less myocardial dysfunction More blood flow heterogeneity Sometimes even without wall motion abnormalities Still supply is sufficient for the demand Dobutamine Dipyridamol 21
Dipyridamol vs Exercise Stress Echo testing Dipyridamol vs Exercise Stress Echo testing 22
Dipyridamol vs Dobutamine Stress Echo Meta analysis of major trials comparing Dipyridamol with Exercise Stess Testing Sensitivity Specificity Accuracy SVD MVD GLOBAL Dipyridamol 66 81 72 92 77 Exercise 72 90 79 82 80 23
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