Presentation on theme: "Exercise Stress Electrocardiography Dr Bijilesh.U."— Presentation transcript:
Exercise Stress Electrocardiography Dr Bijilesh.U
Exercise is a common physiological stress used to elicit cardiovascular abnormalities not present at rest and to determine adequacy of cardiac function. Exercise ecg - one of the most frequent noninvasive modalities used to assess patients with suspected or proven cardiovascular disease. Estimate likelihood & extent of CAD, the prognosis, determine functional capacity & effects of therapy.
Exercise physiology Exercise protocols Electrocardiographic measurements Nonelectrocardiographic observations Exercise test indications Specific Clinical Applications Safety and risks of exercise testing Termination of exercise
EXERCISE PHYSIOLOGY Exercise - body's most common physiologic stress - places major demands on CVS Exercise considered most practical test of cardiac perfusion and function Fundamentally involves the measurement of work Common biologic measure of total body work is oxygen uptake Cardiac output can increase as much as six-fold
EXERCISE PHYSIOLOGY Acceleration of HR by vagal withdrawal Increase in alveolar ventilation Increased venous return- sympathetic venoconstriction. Early phases - cardiac output increased by augmentation in stroke volume and heart rate Later phases by sympathetic-mediated increase in HR
During strenuous exertion, sympathetic discharge is maximal and parasympathetic stimulation is withdrawn Vasoconstriction of most circulatory body systems - except in exercising muscle, cerebral and coronary circulations Catecholamine release enhances ventricular contractility
As exercise progresses skeletal muscle blood flow is increased O 2 extraction increases by as much as threefold total calculated peripheral resistance decreases systolic blood pressure, mean arterial pressure, and pulse pressure increase Diastolic blood pressure does not change significantly.
V O 2 Total body or ventilatory O2 uptake - amount of O2 extracted from air as the body performs work Determinants of VO2 - cardiac output - peripheral AV oxygen difference Maximal AV difference is constant 15 to 17 mL/dL Vo2 - estimate of maximal cardiac output.
V O 2 can be estimated from treadmill speed and grade Vo2 = (MPH ˣ 2.68 ) ˣ [.1 + ( Grade ˣ 1.8) ] + 3.5 Vo2 can be converted to METS by dividing by 3.5.
M O 2 Myocardial oxygen uptake is the amount of oxygen consumed by the heart muscle Determinants of M O2 – Intramyocardial wall tension - Contractility & HR Mo2 - estimated by - HR & SBP (double product). Exercise-induced angina often occurs at the same Mo2 Higher double product - better myocardial perfusion
Maximum heart rate Maximum heart rate (MHR) : 220 – age Overestimate maximum heart rate in females MHR = 206 − 0.88 (age in years) MHR decreased in older persons Age-predicted maximum heart rate is a useful measurement for safety reasons
Post exercise phase - hemodynamics return to baseline within minutes Vagal reactivation - important cardiac deceleration mechanism after exercise Accelerated in athletes but blunted in chronic heart failure
Metabolic Equivalent Refers to a unit of oxygen uptake in a sitting, resting person Common biologic measure of total body work is the oxygen uptake One MET is equated with the resting metabolic rate (3.5 mL of O2/kg/min) MET value achieved from an exercise test is a multiple of the resting metabolic rate
METS associated with activity = Measured Vo2 / 3.5 (both in mL O2/kg/min) Measured directly (as oxygen uptake) or estimated from the maximal workload achieved - using standardized equations
Calculation of METs on the Treadmill METs = Speed x [0.1 + (Grade x 1.8)] + 3.5 3.5 Calculated automatically by Device!
Clinically Significant Metabolic Equivalents for Maximum Exercise 1 METResting 2 METsLevel walking at 2 mph 4 METsLevel walking at 4 mph <5 METsPoor prognosis; peak cost of basic activities of daily living 10 METsPrognosis with medical therapy as good as coronary artery bypass surgery; unlikely to exhibit significant nuclear perfusion defect 13 METsExcellent prognosis regardless of other exercise responses 18 METsElite endurance athletes 20 METsWorld-class athletes
Exercise Test Modalities Isometric, dynamic, and a combination of the two. Isometric exercise - constant muscular contraction without movement Moderate increase in cardiac output and only a small increase in vo2 - insufficient to generate an ischemic response. Dynamic exercise - rhythmic muscular activity resulting in movement
Exercise Protocols Dynamic protocols are most frequently used to assess cardiovascular reserve Should include a low-intensity warm-up and a recovery or cool-down period Optimal for diagnostic and prognostic purposes - Approximately 8 to 12 minutes of continuous progressive exercise - myocardial oxygen demand elevated to patient's maximum
Arm Ergometry Bicycle Ergometry Treadmill Protocol Walk Test
Arm Ergometry Involve arm cranking at incremental workloads of 10 to 20 watts for 2- or 3-minute stages HR & BP responses to a given workload > leg exercise Peak vo2 and peak HR - 70% of leg testing Bicycle Ergometry Involve incremental workloads starting at 25 – 50 watts Lower maximal VO2 than the treadmill
Treadmill Protocol s Bruce Modified Bruce Naughton and Weber ACIP (Asymptomatic cardiac ischemia pilot trial) Modified ACIP
Tread mill protocol Bruce multistage maximal treadmill protocol 3 minutes periods to achieve steady state before workload is increased Limitation - relatively large increase in vo2 between stages Modified Bruce protocol - Older individuals or those whose exercise capacity is limited Modified by two 3 min warm up stages at 1.7mph % 0 % grade and 1.7mph % 5%grade.
Naughton and Weber protocols use 1-2min stages with 1-MET increments between stages Asymptomatic cardiac ischemia pilot trial and modified ACIP protocols use 2min stages with 1.5mets increments between stages - after two 1min warm up Functional capacity overestimated by 20% -if handrail support is permitted
Walk Test A 6-minute walk test or a long-distance corridor walk Provide an estimate of functional capacity in patients who cannot perform bicycle or treadmill exercise Older patients,heart failure, claudication, or orthopedic limitations Walk down a 100-foot corridor at their own pace - cover as much ground as possible in 6 minutes Total distance walked is determined and the symptoms experienced by the patient are recorded.
Cardiopulmonary Exercise Testing Involves measurements of respiratory oxygen uptake (vo2), carbon dioxide production ( vco2 ) and ventilatory parameters during a symptom- limited exercise test Patient wears a nose clip and breathes through a nonrebreathing valve
Technique No caffeinated beverages or smoke 3hr before Wear comfortable shoes and clothes. Unusual physical exertion should be avoided Brief history & physical examination performed Explain risks and benefits Informed consent is taken
12 lead ECG is recorded with electrodes at the distal extremities Torso ECG is obtained in supine & standing position If false +ve test is suspected, hyperventilation should be performed
Room temp should be 18 –24 C & humidity < 60% Walking should be demonstrated to the patient HR, BP & ECG recorded at end of each stage. Resuscitator cart, defibrillator and appropriate cardioactive drugs should be available
Optimal patient position in the recovery phase ? supine Sitting position, less space is required and patients are more comfortable Supine position increases end-diastolic volume and has the potential to augment ST-segment changes
Lead system Mason-Likar modification Modification of the standard 12-lead ECG Extremity electrodes moved to torso to reduce motion artefact Results in right axis shift increased voltage in inferior leads loss of inferior Q waves new Q waves in lead aVL
Types of ST-Segment Displacement J point, or junctional, depression - normal finding in exercise In myocardial ischemia, ST segment becomes horizontal, With progressive exercise depth of ST segment may increase In immediate post recovery phase ST segment displacement may persist with down sloping ST segments and T wave inversion - returning to baseline after 5-10 min In 10%, ischemic response may appear in recovery phase
PQ junction is chosen as isoelectric point TP segment is true isoelectric point but impractical choice Abnormal ST depression 0.1mv (1mm) or > ST depression from PQ junction with a flat ST segment slope ( <0.7-1mv /sec) 80 msec after J point (ST 80) in 3 consecutive beats with a stable base line Measurement of ST-Segment Displacement
When ST 80 measurement difficult at rapid heart rates > 130/mt measure at ST 60 When ST is depressed at rest- additional 0.1mv or more during exercise is considered abnormal
0.1mv ( 1mm) or greater of ST elevation, at ST 60 in 3 consecutive beats - abnormal response. More frequently with AWMI - early after event - decreases in frequency by 6 weeks ST elevation is relatively specific for territory of ischemia ST segment elevation
In leads with abnormal Q waves - not a marker of more extensive CAD and rarely indicates ischemia. When it occurs in non q wave lead in a patient without previous MI - transmural ischemia In a patient who has regenerated embryonic R waves after AMI - significance similar
Eight typical exercise ecg patterns at rest and at peak exertion
T Wave Changes Transient conversion of a negative T wave at rest to positive T wave in exercise – pseudonormalisation Nonspecific finding in patients without prior MI Does not enhance diagnostic or prognostic content of test
Normal exercise response - increase SBP progressively with increasing workloads. Range from 160 to 200 - higher range in older patients with less compliant vessels Abnormal Failure to increase SBP > 120 mm Hg Sustained decrease greater than 10 mm Hg Fall in SBP below resting values Diastolic BP doesn’t change significantly Blood pressure
Conditions other than myocardial ischemia associated with abnormal BP response Cardiomyopathy Cardiac arrhythmias LVOT obstruction Antihypertensive drugs Hypovolemia An exaggerated BP increase with exercise - increased risk of future hypertension
Maximal Work Capacity Important prognostic measurement of exercise test Limited exercise capacity - increased risk of fatal and nonfatal cardiovascular events In one series - adjusted risk of death reduced by 13% for each 1-MET increase in exercise capacity Estimates of peak functional capacity for age and gender - known for most protocols
Heart rate response Sinus rate increases progressively with exercise. Inappropriate increase in heart rate at low work loads - Atrial fibrillation Physically deconditioned Hypovolumic Anemia Marginal left ventricular function
Chronotropic incompetence Decreased heart rate sensitivity to the normal increase in sympathetic tone during exercise Inability to increase heart rate to at least 85%of age predicted maximum. Associated with adverse prognosis
Chronotropic index Refers to heart rate increment per stage of exercise that is below normal. Indicates Autonomic dysfunction Sinus node disease Drug therapy(beta blockers). Myocardial ischemic response When less than 80%, long term mortality is increased
Heart Rate Recovery(HRR) Abnormal HRR refers to a relatively slow deceleration of heart rate following exercise cessation Reflects decreased vagal tone - associated with increased mortality Value of 12 beats/min or less - abnormal
Chest discomfort Development of typical angina during exercise can be a useful diagnostic finding Chest discomfort usually occurs after the onset of ST segment abnormality Exercise-induced angina and a normal ECG requires assessment using a myocardial imaging
Rate-Pressure Product Heart rate SBP product - indirect measure of myocardial oxygen demand Increases progressively with exercise Normal individuals develop a peak rate pressure product of 20 to 35 mm Hg ˣ beats/min ˣ 10 −3 With significant CAD rate-pressure product< 25 Cardio active drug significantly influences this
Diagnostic Use of Exercise Testing In patients with CAD - Sensitivity 68% & specificity - 77% In SVD -- sensitivity is 25-71% In multivessel CAD-- sensitivity is 81%, specificity is 66% Left main or 3vd -- sensitivity is 86%, specificity is 53%
INDICATION FOR EXERCICE ECG FOR DIAGNOSIS. ACC/AHA Guidelines 2002 I Patients with intermediate pretest probability of CAD based on age, gender, and symptoms, including those with complete RBBB or <1 mm of ST-segment depression at rest IIa Patients with suspected vasospastic angina iii 1. Patients with baseline electrocardiographic abnormalities: a. Preexcitation (Wolff-Parkinson-White) syndrome b. Electronically paced ventricular rhythm c. >1 mm of ST-segment depression at rest d. Complete left bundle branch block 2. Patients established diagnosis of CAD because of prior MI or CAG; however, testing can assess functional capacity and prognosis
Noncoronary Causes of ST-Segment Depression Anaemia Cardiomyopathy Digitalis use Hyperventilation Hypokalemia IVCD LVH MVP Severe AS Severe HTN Severe hypoxia SVT & Preexcitation
Brody effect As exercise progress R wave amplitude increase normally till HR around 130, after that amplitude decrease Indicates normal or minimal LV dysfunction and is associated with normal CAG Increase R wave amplitude in post exercise period indicates ischemia and LV dysfunction May be related to an increase in LV end-diastolic volume due to exercise-induced LV dysfunction.
Bayes’ Theorem Incorporates pretest risk of disease & sensitivity and specificity of test to calculate post-test probability of CAD Clinical information and exercise test results are used to make final estimate about probability of CAD Diagnostic power maximal when pretest probability of CAD is intermediate (30% to 70%)
EXERCISE PARAMETERS ASSOCIATED WITH MULTIVESSEL CAD Duration of symptom-limiting exercise < 5 METs Abnormal BP response Angina pectoris at low exercise workloads ST-depression ≥ 2 mm - starting at <5 METs down sloping ST - involving ≥5 leads, - ≥5 min into recovery Exercise-induced ST- elevation (aVR excluded) Reproducible sustained or symptomatic VT
. Exercise Testing in Determining Prognosis Asymptomatic population Prevalence of abnormal TMT in asymptomatic middle aged men - 5-12%. Risk of developing a cardiac event- approximately nine times when test abnormal Future risk of cardiac events is greatest if test strongly positive or with multiple risk factors Appropriate asymptomatic subjects for test - estimated annual risk > 1 or 2% per year
Symptomatic patients Exercise ECG should be routinely performed in patients with chronic CAD before CAG Patients with good effort tolerance (>10 METS) have excellent prognosis regardless of anatomical extent of CAD. Provides an estimate of functional significance of CAG documented coronary stenoses
RISK ASSESSMENT AND PROGNOSIS in PATIENTS WITH SYMPTOMS OR PRIOR HISTORY OF CAD CLASS INDICATION ACC/AHAGuidelines 2002 I 1. Patients undergoing initial evaluation Exceptions a. Preexcitation syndrome b. Electronically paced ventricular rhythm c. >1 mm of ST-segment depression at rest d. Complete left bundle branch block 2. Patients after a significant change in cardiac symptoms 3. Low-risk unstable angina patients 8 to 12 hr after presentation who have been free of active ischemic or heart failure symptoms 4. Intermediate-risk unstable angina patients 2 to 3 days after presentation who have been free of active ischemic or heart failure symptoms III Patients with severe comorbidity likely to limit life expectancy or prevent revascularization
Duke tread mill score Developed by Mark and co-workers Provide survival estimates based on results from exercise test Provides accurate prognostic & diagnostic information Adds independent prognostic information to that provided by clinical data & coronary anatomy Less effective in estimating risk in subjects > 75
Duke tread mill score Exercise time - (5 ˣ ST deviation) - (4 ˣ treadmill angina index) Angina index 0-if no angina 1-if typical angina occurs during exercise 2-if angina was the reason pt stopped exercise
Duke tread mill score - RISK ScoreRisk5 yr survival %CAD > 5Low risk97Nil / SVD - 10 to +4Moderate risk91 < -11High risk72TVD/LMCA
After MI Exercise testing is useful to determine Risk stratification Functional capacity for activity prescription Assessment of adequacy of medical therapy Incidence cardiac events with test after MI is low Slightly greater for symptom-limited protocols
Risk Stratification Before Discharge after MI : Class I Recommendations for exercise test ACC/AHA Guidelines For low-risk patients who have been free of ischemia at rest or with low-level activity and of HF for a minimum of 12 to 24 hr For patients at intermediate risk who have been free of ischemia at rest or with low- level activity and of HF for a minimum of 12 to 24 hr
SUBMAXIMAL TEST Performed within 3 to 4 days in uncomplicated patients Low-level exercise test – achievement of 5 to 6 METs 70% to 80% of age-predicted maximum HR A 3- to 6-week test - for clearing patients to return to work in occupations with higher MET expenditure
Preoperative Risk Stratification before Noncardiac Surgery Provides an objective measurement of functional capacity Identify likelihood of perioperative myocardial ischemia Perioperative cardiac events - significantly increased with abnormal test at low workloads Consider CAG with revascularization before high risk surgery in such patients
VPCs are common during exercise test & increase with age. Occur in 0-5% of asymptomatic subjects - no increased risk of cardiac death Suppression of VPCs during exercise is nonspecific. In patients with recent MI, presence of repetitive VPC is associated with increased risk of cardiac events. Cardiac arrhythmias & conduction disturbances
Ventricular arrhythmia Exercise testing provokes VPCs in most patients with h/o sustained ventricular tachyarrhythmia. VPC in early post exercise phase is associated with worse long term prognosis RBBB morphology was associated with increased 2-year mortality rate than LBBB
Supraventricular arrhythmias Premature beats are seen in 4-10%of normal persons & 40%of patients with heart disease. Sustained arrhythmia occur in 1-2%. Atrial fibrillation Rapid ventricular response is seen in initial stages of exercise Effect of digitalis & beta-blockers on attenuating this can be assessed by exercise testing
Sinus node dysfunction Lower heart rate response may be seen at submaximal and maximal workloads Atrioventricular block In congenital AV block, exercise induced heart rate is low In acquired diseases, exercise can elicit advanced AV block
LBBB Exercise-induced ST depression is seen in patients with LBBB & cant be used as diagnostic indicator. New development of LBBB - 0.4% Relative risk of death or other major cardiac events with new exercise-induced LBBB - increased three fold.
RBBB Indicators CAD in RBBB 1.new onset ST depression in V5 & V6, or L II or avF 2.reduced exercise capacity 3.inability to adequately increase systolic BP Exercise induced ST depression leads V1-V4 common with RBBB -non-diagnostic
Preexcitation syndrome WPW syndrome invalidates use of ST segment analysis as a diagnostic method. False +ve ischemic changes are seen Exercise may normalise QRS complex with disappearance of delta waves in 20-50% more frequent with left sided than right sided pathway
Exercise Testing in Heart Rhythm Disorders Class I Adults with ventricular arrhythmias with intermediate or greater probability of CAD In patients with known or suspected exercise- induced ventricular arrhythmias Class IIa For evaluating response to medical or ablation therapy in exercise-induced ventricular arrhythmias
Cardiac pacemakers To assess performance following CRT in patients with heart failure and ventricular conduction delay Ideal pacemaker should normalize the heart rate response to exercise
ICD When testing patients with ICD program detection interval of the device should be known If ICD is implanted for VF or fast VT rate will normally exceed that attainable during sinus tachycardia Test terminated as the HR approaches 10 beats/min below the detection interval With slower detection rates, ICD reprogrammed to a faster rate - avoid accidental discharge during exercise testing Can be temporarily deactivated by a magnet.
Influence of drugs and other factors Smoking reduces ischemic response threshold. Hypokalemia & digoxin - exertional ST depression Nitrates, beta blockers, CCB Prolong the time to onset of ST depression Increase exercise tolerance
Women Diagnostic accuracy is less in women due to lower prevalence of CAD. False +ve results are common during menses or preovulation, & in postmenopausal women on estrogen therapy
Elderly patients Started at slowest speed with 0% grade and adjusted according patient’s ability Frequency of abnormal results is more and risk of cardiac events also more Subjects > 75 years Duke treadmill scoring system is less useful Diabetes mellitus In patients with autonomic dysfunction and sensory neuropathy anginal threshold is increased and abnormal HR and BP response is common
Valvular heart disease Provide information on timing of operative intervention and estimate degree of incapacitation Aortic stenosis With moderate to severe AS exercise testing can be safely performed with appropriate protocols Hypotension during test in asymptomatic patients with AS is sufficient to consider for valve replacement
In the young adult with AS with - mean gradient > 30 mm Hg or a peak velocity > 3.5 m/sec - before athletic participation - Class IIa Increase in mean gradient by 18, ecg changes, blunted BP response – predict cardiac events Symptomatic patients with AS - Class III
MS In patients with MS, Excessive HR response to low levels of exercise Exercise-induced hypotension & chest pain - Favor earlier valve repair
HOCM To determine exercise capability, symptoms, ECG changes or arrhythmias, or increase in LVOT gradient - Class IIa Inability to increase BP by 20 mm Hg during exercise is associated with adverse prognosis High resting gradients,NYHA class III or IV symptoms, h/o ventricular arrhythmias - not tested.
Coronary bypass grafting ST depression may persist when revascularisation is incomplete Also in 5% of persons with complete revascularisation After CABG Stress imaging better than exercise ECG Late abnormal exercise response may indicate graft occlusion or stenosis
Percutaneous coronary intervention Low detection rate of restenosis in the early phase (< 1month) Early abnormal result Suboptimal result Impaired coronary vascular reserve in a successfully dilated vessel Incomplete revascularization 6-12 month post procedure test – detect restenosis Initial normal test to an abnormal result in the initial 6 months usually associated with restenosis
Cardiac transplantation Maximal O2 uptake & work capacity improved as compared with pre-operative findings. Abnormalities that may be seen are 1.resting tachycardia 2.slow HR response during mild to moderate exercise 3.more prolonged time for HR to return to baseline during recovery
Safety and risks of TMT Mortality is < 0.01%, morbidity is <0.05% Risk of major complication is twice when symptom limited protocol is used Risk is greater when test is performed soon after an acute event. Early postinfarction phase risk of fatal complication during symptom-limited testing - 0.03%.
Recent significant change in the rest electrocardiogram Acute myocardial infarction (within 2 days) High-risk unstable angina Uncontrolled cardiac arrhythmias causing symptoms or hemodynamic compromise Symptomatic severe aortic stenosis Uncontrolled symptomatic heart failure Acute pulmonary embolus or pulmonary infarction Acute myocarditis or pericarditis Acute aortic dissection Acute systemic infection accompanied by fever, body aches, or lymphadenopathy Absolute Contraindications to Exercise Testing ACC/AHA Guidelines:
Left main coronary stenosis Severe arterial hypertension (systolic blood pressure > 200 mm Hg and/or diastolic blood pressure > 110 mm Hg) Tachyarrhythmias or bradyarrhythmias Hypertrophic cardiomyopathy and other forms of outflow tract obstruction High-degree atrioventricular block Neuromuscular, musculoskeletal, or rheumatoid disorders Ventricular aneurysm Relative Contraindications to Exercise Testing ACC/AHA Guidelines:
TERMINATION OF EXERCISE Absolute indications Moderate to severe angina Increasing nervous system symptoms (eg, ataxia, dizziness, or near-syncope) Technical difficulties in monitoring ECG or systolic blood pressure Subject's desire to stop Sustained ventricular tachycardia ST-segment elevation (1.0 mm) in leads without diagnostic Q waves (other than V 1 or aVR) Relative indications Drop in systolic blood pressure of 10 mm Hg from baseline blood pressure ST-segment depression (> 3 mm of horizontal or downsloping) Other arrhythmias - multifocal PVCs, triplets of PVCs, SVT, heart block, or bradyarrhythmias Fatigue, shortness of breath, wheezing, leg cramps, or claudication Development of bundle branch block or IVCD indistinguishable from VT Hypertensive response ( SBP > 250 mm Hg and/or a diastolic BP > 115 mm Hg)