Exercise Stress Electrocardiography
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Transcript of Exercise Stress Electrocardiography
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Exercise Stress Electrocardiography
Dr Bijilesh.U
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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.
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Exercise physiology
Exercise protocols
Electrocardiographic measurements
Nonelectrocardiographic observations
Exercise test indications
Specific Clinical Applications
Safety and risks of exercise testing
Termination of exercise
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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
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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
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During strenuous exertion, sympathetic discharge is maximal and parasympathetic stimulation is withdrawn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
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As exercise progresses
skeletal muscle blood flow is increased
O2 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.
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V O2
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.
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V O2 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.
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M O2
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
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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
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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
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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
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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
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Calculation of METs on the Treadmill
METs = Speed x [0.1 + (Grade x 1.8)] + 3.5
3.5
Calculated automatically by Device!
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Clinically Significant Metabolic Equivalents for Maximum Exercise
1 MET Resting
2 METs Level walking at 2 mph
4 METs Level walking at 4 mph
<5 METs Poor prognosis; peak cost of basic activities of daily living
10 METs Prognosis with medical therapy as good as coronary artery bypass surgery; unlikely to exhibit significant nuclear perfusion defect
13 METs Excellent prognosis regardless of other exercise responses
18 METs Elite endurance athletes
20 METs World-class athletes
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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
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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
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Arm Ergometry Bicycle Ergometry Treadmill Protocol Walk Test
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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
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Treadmill Protocol s
Bruce Modified Bruce Naughton and Weber ACIP (Asymptomatic cardiac ischemia pilot trial) Modified ACIP
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Tread mill protocolBruce 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.
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• 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
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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.
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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
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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
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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
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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
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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
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Electrocardiographic Measurements
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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
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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
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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
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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
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1.PQ JUNCTION2. J POINT3.ST 80
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Upsloping ST segment
Rapid upsloping ST segment (more than 1 mV/sec) depressed less than 1.5 mm after the J point - normal
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Slow upsloping ST segment at peak exercise
In patients with high CAD prevalence, slow up sloping ST ,depressed > 1.5mm ST 80 is considered abnormal
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Horizontal ST-segment depression
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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
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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
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Eight typical exercise ecg patterns at rest and at peak exertion
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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
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Nonelectrocardiographic Observations
Blood pressure Maximal Work Capacity Heart rate response Heart Rate Recovery Chest discomfort Rate-Pressure Product
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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
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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
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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
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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
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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
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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
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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
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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
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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%
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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
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Noncoronary Causes of ST-Segment Depression
Anaemia Cardiomyopathy Digitalis use Hyperventilation Hypokalemia IVCD
LVH
MVP Severe AS Severe HTN Severe hypoxia SVT & Preexcitation
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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.
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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%)
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PRETEST PROBABILITY
AGE (yr) GENDERTYPICAL ANGINA
ATYPICAL ANGINA
NONANGINAL CHEST PAIN
ASYMPTOMATIC
30-39 Men Intermediate Intermediate Low Very low
Women Intermediate Very low Very low Very low
40-49 Men High Intermediate Intermediate Low
Women Intermediate Low Very low Very low
50-59 Men High Intermediate Intermediate Low
Women Intermediate Intermediate Low Very low
60-69 Men High Intermediate Intermediate Low
Women High Intermediate Intermediate Low
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EXERCISE PARAMETERS ASSOCIATED WITHMULTIVESSEL 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
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. 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
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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
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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
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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
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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
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Duke tread mill score - RISK
Score Risk 5 yr survival % CAD
> 5 Low risk 97 Nil / SVD
- 10 to +4 Moderate risk 91
< -11 High risk 72 TVD/LMCA
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SPECIFIC CLINICAL APPLICATIONS
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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
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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
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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
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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
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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
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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
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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
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Sinus node dysfunctionLower heart rate response may be seen at submaximal and maximal workloads
Atrioventricular blockIn congenital AV block, exercise induced heart rate is low
In acquired diseases, exercise can elicit advanced AV block
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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.
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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MS
In patients with MS,
Excessive HR response to low levels of
exercise
Exercise-induced hypotension & chest pain
- Favor earlier valve repair
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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.
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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
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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
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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
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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%.
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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:
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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:
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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 V1 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)
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