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During strenuous exertion, sympathetic discharge is maximal and parasympathetic stimulation is withdrawn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

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.

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.

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.

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

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 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

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 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.

• 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

Electrocardiographic Measurements

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

1.PQ JUNCTION2. J POINT3.ST 80

Upsloping ST segment

Rapid upsloping ST segment (more than 1 mV/sec) depressed less than 1.5 mm after the J point - normal

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

Horizontal ST-segment depression

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

Nonelectrocardiographic Observations

Blood pressure Maximal Work Capacity Heart rate response Heart Rate Recovery Chest discomfort Rate-Pressure Product

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

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%)

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

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

. 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

Score Risk 5 yr survival % CAD

> 5 Low risk 97 Nil / SVD

- 10 to +4 Moderate risk 91

< -11 High risk 72 TVD/LMCA

SPECIFIC CLINICAL APPLICATIONS

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 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

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 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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