Stress Testing for Ischemia and Viability



Stress Testing for Ischemia and Viability


Daniel H. Cooper

Thomas K. Kurian





Key Points



  • Echocardiographic stress testing is a sensitive and specific modality for detecting the presence of stress-induced ischemia in appropriately selected patients.


  • Ischemia manifests as regional wall motion abnormalities and changes in myocardial thickening during stress.


  • Exercise echocardiography yields additional prognostic information and is preferred to pharmacologic stress testing.


  • Causes of false negative results include: Failure to reach target heart rate, delayed peak stress image acquisition, single-vessel disease especially involving the circumflex artery, anti-anginal/beta-blocker use before testing.


  • Causes of false positive results include: HTN, LVH, coronary spasm, paradoxical septal motion secondary to conduction abnormality (LBBB, pacing).


  • To avoid these pitfalls, recognize the importance of achieving an adequate level of stress (>85% MPHR), timely image acquisition (<60 s for exercise echo protocols), and confirming wall motion abnormalities in multiple views.


  • Dobutamine stress echocardiography can be utilized to confirm myocardial viability by noting the presence of a biphasic response to increasing rates of dobutamine infusion.


General Principles



  • The use of stress echocardiography for detection of ischemia is based on the principles outlined by the ischemic cascade (see Fig. 6-1).


  • Impaired myocardial perfusion due to coronary artery disease (CAD) leads to a progression of manifestations during exercise or pharmacologic stress that ultimately results in regional or global wall motion or thickening abnormalities.


  • The goal is to determine whether ischemia is present or, if there are baseline wall motion abnormalities and reduced LVEF, if there is viable myocardium and LV contractile reserve.


  • Obtaining an adequate level of stress is vital to maintaining the modality’s sensitivity for detecting CAD.



    • Achieving 85% of the maximally predicted heart rate (MPHR = 220 – Age) improves sensitivity greatly.


    • However, if changes consistent with ischemia are detected at lower (submaximal) levels of stress, this improves specificity of the result.







      Figure 6-1. Ischemic cascade showing at what stage stress echocardiography and nuclear stress detect changes. (Schinkel AFL, Bax JJ, Geleijnse ML, et al. Noninvasive evaluation of ischaemic heart disease: myocardial perfusion imaging or stress echocardiography? Eur Heart J. 2003;24:789–800, by permission of Oxford University Press.)


  • Continuous patient monitoring by medical staff is required, including frequent symptom inquires, continuous ECG, and intermittent BP measurement.



    • Crash carts, stocked with resuscitation equipment and medications, should be available.


    • Risk of MI/Death ∼1/2500


Anatomy



  • Stress echocardiography typically focuses on images obtained in the apical (four- and two-chamber) and parasternal (short- and long-axis) views, allowing for observation of all myocardial segments.


  • Knowledge of the typical distribution of coronary artery blood flow to the various myocardial segments is vital. It allows:



    • Confirmation in multiple views of suspected lesions, especially when image quality in one view is suboptimal.


    • Correlation of findings to specific location(s) of coronary artery stenosis (Fig. 6-2).



      • LAD: Anterior, anteroseptal, apex, +/- inferoapical (wrap-around LAD)


      • Circumflex: Anterolateral, inferolateral


      • RCA: Inferior, inferoseptal (basal, mid), +/- inferolateral (depending on dominance)


      • Distal versus proximal: A proximal LAD lesion; for example, will result in basal to distal wall motion abnormalities of the anteroseptum (septal perforators) and anterior wall (diagonal) whereas distal LAD disease will affect only the apex.







        Figure 6-2. The standard echocardiographic views demonstrating the 17-segment model color-coded for typical coronary artery distribution. (Reprinted from Lang RM, Bierig M, Devereux RB, et al. Recommendations for Chamber Quantification: A Report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group, Developed in Conjunction with the European Association of Echocardiography, a Branch of the European Society of Cardiology. JASE. 2005;18:1440–1463, with permission from Elsevier.)


Exercise Stress Echocardiography



  • In general, all exercise stress protocols involve staged increases in workload to increase myocardial oxygen demand. This is accomplished by treadmill or stationary bicycle exercise.



    • The Bruce protocol (most common) involves symptom-limited exercise on the treadmill where grade and speed increases every 3 minutes.


    • METS (metabolic equivalents) are calculated automatically by the machine and is important to report as a prognostic indicator (<5 METS suggests poor prognosis if <65 years old).


Absolute Contraindications

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Oct 20, 2016 | Posted by in CARDIOLOGY | Comments Off on Stress Testing for Ischemia and Viability

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