CHAPTER SIX Interpretation of Clinical Test Data Posttest probability of disease is determined by pretest probability and the probability of the test providing a true result Pretest probability determined mainly by angina but also by major risk factors Exercise testing in the apparently healthy not recommended

INTERPRETING THE DATA Purpose of the test and patient conditions including medications and resting ECG abnormalities Objectives of exercise testing address : exercise tolerance, max VO2, hemodynamics (HR, BP), changes associated with electrical functions of heart and limiting signs or symptoms

WHAT DETERMINES MAXIMAL EFFORT? Failure of HR to increase with increase in exercise Plateau in oxygen consumption--hard to determine Lactic acid measure of > 8 mmol RPE > 17 ( 6-20 scale)

HR and BP RESPONSE Inability to appropriately increase HR and/or delayed decrease in recovery HR usually indicate heart disease and impact prognosis Drop or failure to increase SBP with increasing exercise is abnormal Normal postexercise SBP presents as a progressive decline with a greater drop during passive recovery

ABNORMAL BP RESPONES SBP greater than 250 mmHg is criteria for test termination DBP greater than 114 mmHg (115 mmHg in book) is criteria for test termination

MORE RPP= SBP X HR represent myocardial oxygen consumption--ischemia happens at a reproducible product Increase of DBP > 10 mmHg questionable as to disease Some medications make BP responses hard to evaluate

ECG WAVEFORMS Test 2 – You’ll need to know PQRST and be able to determine HR from an ECG strip

DIAGNOSTIC VALUE OF EXERCISE TESTING To detect for CAD Sensitivity Specificity Prevalence Predictive value--positive and negative

SENSITIVITY Refers to the percent of patients that have disease and test positive for disease= true positive test A false negative test fails to identify a patient with disease See box 6-3 for causes leading to false negative tests

SENSITIVITY Test sensitivity is decreased by failure to reach maximum stress, meds, and poor ECG monitoring Using the correct precordial leads increase sensitivity

SPECIFICITY The percent of patients considered normal that present with negative tests=true negative-see box 6-4 for causes for FP A false positive test incorrectly identifies a person as having disease when they do not Sensitivity and Specificity of exercise testing vary based on patient selection, test protocols, and ECG criteria for CAD Sensitivity=68% and Specificity=77%

PREDICTIVE VALUE Predictive value measures how accurately a test result identifies a person with or without disease Predictive value is driven by disease prevalence in the population under study