EXERCISE STRESS TEST Physiology and Protocol,

Indications and Contraindications

DN

• Essential ET Terminology

• Performance of the E S T

• Assess Exercise Test Responses

• Interpretation Of The Exercise Stress Test

Exercise Test Terminology

• Vo2max

• METs

• Myocardial Oxygen Consumption

Maximal Oxygen Uptake (VO2max)

• Greatest amount of oxygen an individual utilizes with maximal exercise (ml O2 /kg/ min)

• “Gold Standard” for cardiorespiratory fitness

• Fick EquationVo2max = (HRmax x SVmax) x (CaO2max -

CvO2max)

VO2max = (HRmax X SVmax) X (CaO2max - CvO2max)Genetic Factors (Heart Size)Conditioning Factors Contractility/Afterload/PreloadDisease Factors Wall Motion/Ventricular Fn, Valve Stenosis or Regur

Skeletal Muscles• Aerobic Enzymes• Fiber Type• Muscle Disease• Cap density

PaO2

Hgb [ ]

SaO2

DiffusionVentilationPerfusion

FICK EQUATION

(220 - Age)

Sinus Node Dysfunction

Drugs (e.g., B - blockers)

MET

•Metabolic Equivalent Term

•1 MET = "Basal" aerobic oxygen consumption to stay alive = 3.5 ml O2 /Kg/min

• inf- thyroid status, post exercise, obesity, disease states

MET Values

• 1 MET = "Basal" = 3.5 ml O2 /Kg/min

• 2 METs = 2 mph on level

• 4 METs = 4 mph on level

• < 5METs = Poor prognosis if < 65;

10 METs = prognosis with med therapy =

CABG

13 METs = Excellent prognosis

16 METs = Aerobic master athlete

Calculation of METs on the Treadmill

METs = Speed x [0.1 + (Grade x 1.8)] + 3.5

3.5

Calcul automatically by device

Speed in meters/minute = MPH x 26.8

Grade expressed as a fraction

Myocardial (MO2) Accurate measurement - cardiac catheterization

Coronary Flow x Coronary (a – v)O2 diff

HR, SBP, LVEDV, CONTRACTILITY, WALL THICKNESS

.

Myocardial Oxygen Consumption

• Indirectly measured as the “Double Product”

• “Double Product” = HR x SBP

– A normal value is greater than 20,000 – 25,000

– < 20,000 is low heart work load– > 29,000 indicates high heart work load

• Angina & ST↓occur at the same DP for an individual

Types of Exercise1. Isometric (Static)

-weight-lifting -pressure work for heart, limited

cardiac output

2. Isotonic (Dynamic) -walking, running, swimming, cycling -Flow work for heart -↑CO,↓ TPR

3. Mixed

Exercise physiology

• Sympathetic activation• Parasympathetic withdrawal• Vasoconstriction, except in-

– Exercising muscles– Cerebral circulation – Coronary circulation

• ↑norepinephrine and renin

Exercise physiology

• ↑ventri contractility

• ↑O2 extraction(upto 3)

• ↓peripheral resistance

• ↑SBP,MBP,PP

• DBP –no significant change

• Pulm vasc bed can accommodate 6 fold CO

• CO - ↑ 4-6 times

Exercise physiology

Isotonic exercise(cardiac output)• Early phase- SV+HR• Late phase-HR

• peak oxygen consumption- age, sex, & training level of the person performing the exercise

• The plateau in peak oxygen consumption- Vo2 max

• Vo2 max is limited by

1)the ability to del O2 to sk. muscles 2) muscle oxidative capacity .

Oxygenconsumption(liters/min)

Work rate (watts)

V02 peak

(VO2max)

• dynamic exercise- ventilation increases linearly over the mild to moderate range, then > rapidly in intense exercise

• workload at which rapid ventilation occures is called the ventilatory breakpoint (together with lactate threshold)

Respiration during exercise

Lactate acidifies the blood, driving off CO2 and increasing ventilatory rate

BP rise in exercise

• (SBP) ↑up to 150-170 mm Hg during dynamic exercise; diastolic rarely alters

• isometric - SBP may ≥250 mmHg, and DBP can reach 180

Bloodlacticacid(mM)

Relative work rate (% V02 max)

Intense exercise Glycolysis>aerobic metabolism ↑ blood lactate

Lactate threshold; endurance estimation

Age Pred Max HR

• APMHR=220 - age in years\• APMHR=200-1/2 age

• MHR ↓ with age• Lower/higher than actual value(+/_12beats)• Not used as an indicator of max exertion in

EST/ Indi to terminate test

.

Post exercise phase

• Vagal reactivation -Imp-cardiac decceleration mech

• ↑in well trained athletes

• Blunted in CCF

ENERGY REQ ACTIVITY

1 MET TAKING CARE OF SELFWALKING INDOORSWALK AT 2-3 mph

4 METS LIGHT WORK AROUND THE HOUSEWALKING AT 3-4 mph

>4-<10 METS CLIMB 1 FLIGHT OF STAIRS/UP HILLWALK>4 mph, SHORT RUNNINGSCRUBBING FLOOR,MOVING FURNITURE

>10 METS RUNNING> 6-7 mphHEAVY LABOURSWIMMING,FOOTBALL

Exercise Stress Testing

• Pathophysiology:

– At rest- adequate coronary blood flow– with exercise-supply\demand mismatch -ST

segment changes

– 70-80%occlusion - detection by EST

– Sign CAD can exist with a -VE Exercise Stress Test.

Treadmill protocol EST- stand protocols to progressively ↑ cardiovascular

work load in a uniform and reproducible way

• Bruce protocol• Naughton protocol• Weber protocol• ACIP(asymptomatic cardiac ischemia pilot)• Modified ACIP

The Bruce protocol• 1949 by Robert A. Bruce,

considered the “father of exercise physiology”.

• Published as a standardized protocol in 1963.

• gold-standard for detection of myocardial ischemia when risk stratification is necessary.

BRUCE Protocol

Stage Time (min) M/hr Slope

1 0 1.7 10%

2 3 2.5 12%

3 6 3.4 14%

4 9 4.2 16%

5 12 5.0 18%

6 15 5.5 20%

Peak Vo2 is the same regardless of the protocol useddiff – rate at which it is achieved

PROTOCOL USES COMMENTS

BRUCE Normally used large↑Vo2 bet stages\running≥st 3

NAUGHTON&WEBER Limited ex tolerance-CCF 1-2 min stages\1 MET increment

ACIP Established CAD 2 min stages\> linear ↑ in HR & Vo2

MOD-ACIP Short elderly individuals

Procedure

• Standard 12 lead ECG- leads

• Torso ECG + BP– Supine and Sitting / standing

• HR ,BP ,ECG– Before,after,stage – Onset of ischemic response– Each min recovery(5-10 mints)

Procedure- Lead systems

• Mason-Liker modification-extremity electrodes moved to torso 2 ↓ motion artifacts

– RAD– ↑inf lead voltage– Loss of inf lead q– New Q in AVL

Contraindications to Exercise Testing

Absolute• A/c MI (< 2 d)• High-risk unstable angina• Uncontrolled cardiac arrhythmias causing

symptoms or hemo compromise• Symptomatic severe AS• Uncontrolled symptomatic CCF• Acute pulmonary embolus or pulmonary

infarction• A/c myocarditis or pericarditis• A/c Ao dissection

Contraindications to Exercise Testing

Relative• LMCA stenosis• Mod- stenotic VHD• Electrolyte abnormalities• Sev HTN• Tachyarrhythmias or bradyarrhythmias• HOCM and other outflow tract obstructions• Mental or physical impairment leading to

inability to exercise adequately• High-degree AV block

SAFETY & RISKS

In nonselected pat pop-mortality- .01% -morbidity-.05%In k/c CAD- 1 C.arrest/59000 person hours -AMI in 1.4 / 10000 testsArrythmias-AF-Mc-9/10,000 tests -VT-6/10,000 tests -VF- .6/10,000 tests

Deaths& MI estimated occur in 1 of 25000 tests

The post test probability is proportional to the pretest probability

To diagnose, test sensitivity ,specificity& prevalence in the population being tested req

Bayes' theorem A theory of probability

• Sensitivity- a person with the disease having a positive test.

• Specificity-person without the disease having a negative test.

• Prevalence- % in the population having

disease.

Pretest Probability

• Based on the pat's h/o ( age, gender, chest pain ), phy ex and initial testing, and the clinician's experience.

• Typical or definite angina →pretest probability high - test result does not dramatically change the probability.

• Diag power maximal when the pretest probability is intermediate-30-70%

Classification of chest pain

• Typical angina

• Atypical angina

• Noncardiac chest pain

1. Substernal chest discomfort with characterstic quality and duration

2. Provoked by exertion or emotional stress

3. Relieved by rest or NTG

Meets 2 of the above characteristics

Meets one or none of the typical characteristics

Pre Test Probability of Coronary Disease by Symptoms, Gender and Age

Age Gender Typical/DefiniteAngina Pectoris

Atypical/ProbableAngina Pectoris

Non-Anginal

Chest Pain

Asymptomatic

30-39 Males Intermediate Intermediate low (<10%) Very low (<5%)

30-39 Females Intermediate Very Low (<5%) Very low Very low

40-49 Males High (>90%) Intermediate Intermediate low

40-49 Females Intermediate Low Very low Very low

50-59 Males High (>90%) Intermediate Intermediate Low

50-59 Females Intermediate Intermediate Low Very low

60-69 Males High Intermediate Intermediate Low

60-69 Females High Intermediate Intermediate Low

High = >90% Intermediate = 10-90% Low = <10% Very Low = <5%

INTERMEDIATE CATEGORYAGE GROUP GENDER & SYMPTOMS

30-39 YEARS M& F + TYPICAL ANGINA M + ATYPICAL/ PROBABLE ANGINA

40-49 YEARS F + TYPICAL ANGINAM + ATYPICAL/ NON ANGINAL CP

50-59 YEARS F+ TYPICAL ANGINAM&F + ATYPICAL NAGINAM+ NON ACP

60-69 YEARS M& F+ ATYPICAL/PROB ANGINAM&F + NACP

E T TO DIAGNOSE OBSTRUCTIVE CAD

Class I• Adult (including RBBB or <1 mm of resting

ST↓) with intermed pretest probability of CAD

Class IIa• Patients with vasospastic angina.

E T TO DIAGNOSE OBSTRUCTIVE CAD

Class IIb1. Patients - high pretest probability of CAD 2. Patients - low pretest probability of CAD 3. Patients with <1 mm of baseline ST ↓and on digoxin.4. Patients with LVH and <1 mm baseline ST ↓.

Class III1. Patients with the following baseline ECG abnormalities:

• Pre-excitation syndrome• Electronically paced ventricular rhythm• >1 mm of resting ST depression• Complete LBBB

EST SENSITIVITY SPECIFICITY

OVERALL 68% 77%

SVD(LAD>RAD>LCX) 25-71%

MULTIVESSEL DIS 81% 66%

LMCA/3-VD 86% 53%

Exercise Testing in Asymptomatic PersonsWithout Known CAD

Class I • None.

Class IIa• Evaluation of asymP DM pts - plan to start vigorous exercise ( C)

Class IIb• 1. Eval of pts with multiple risk factors - guide to risk-reduction therapy.• 2. Eval of asymptomatic men > 45 yrs and women >55 yrs: Plan to start vigorous exercise Involved in occupations which impact public safety High risk for CAD(e.g., PVOD and CRF)Class III• Routine screening of asymptomatic

RISK ASSESS AND PROGIN PAT WITH SYMP OR APRIOR HISTORY OF CAD

Class I 1. Initial evalu with susp/known CAD +/- RBBB or <1 mm of

resting ST Depression 2.Susp/ known CAD, previously evaluated-+ signi change in

clinical status nw 3. Low-risk UA pts >8 to 12 hrs & free of active

ischemia/CCF 4. Intermed-risk UApts > 2 to 3 days & no active ischemia/

CCFClass IIa Intermed-risk UA pts – initial markers (N),rpt ECG –no signi

change, and markers >6-12 hrs (N) & no other evidence of ischemia during observation.

AFTER MYOCARDIAL INFARCTION

Class I• 1. Before discharge (submaximal --4 to 6 days).• 2. Early after discharge (symptom limited --14 to 21

days).• 3. Late after discharge if the early exercise test was

submaximal (symptom limited --3 to 6 weeks).

Class IIa• After discharge as part of cardiac rehabilitation in

patients who have undergone coronary revascularization.

AFTER MYOCARDIAL INFARCTION

Class IIb1. Patients with the following ECG abnormalities:• • Complete LBBB• • Pre-excit synd• • LVH• • Dig therapy• • >1 mm of resting ST-segment dep• • paced ventricular rhythm2. Periodic monitoring in patients who continue to participate in exercise

training or cardiac rehabilitation.Class III1. Severe comorbidity likely to limit life expectancy and/or candidacy for

revascularization.2. any time to eval pts with AMI with uncompensated CCF, arrhythmia, or

noncardiac exercise limiting conditions. 3. Before discharge to evaluate pts who have already been selected for, or

have undergone, cardiac cath. .

Submaximal protocols • predetermined end point, often a peak HR

120 bpm, or 70% predicted max HR or peak MET – 5

Symptom-limited tests • to continue till signs or sympt needing

termination (i.e., angina, fatigue, ≥ 2 mm of ST↓,v. arrhy, or ≥10-mm Hg drop in SBP from the resting blood pressure)

• The incidence of fatal cardiac events(inclu fatal MI & cardiac rupture)-- 0.03%

• Nonfatal MI and successfully resuscitated cardiac arrest -- 0.09%

• Complex arrhythmias, including VT --1.4%.

• Symptom-limited protocols have an event rate that is 1.9 times that of submaximal tests

High risk predischarge Present Absent

Cardiac cath strategy 2 strategy3

symp lim EST(14-21d) sub max (4-7d)

Symp lim EST(14-21 days) Markedly ab mildly ab negative

Card cath Ex imaging

Reversible ischemia no rev ischemia

Med Rx

Sub max (4-7 days)

Markedly ab mildly ab negative

Ex imaging

Rev ischemia no rev isch

symp lim ex(3-6wks)

card cath markedly ab mildly ab negative

rev isch no rev isch

Med Rx

E S T Before and After RevascularizationClass I• 1. Demo of ischemia before revascularization.• 2. Eval rec symps suggesting ischemia aft revascularization.Class IIa• Aft discharge for activity counseling and/or exercise training as part of

rehabilitation in pts aft revascularization.Class IIb• 1. Detection of restenosis in selected, high-risk asymptomatic pts < first

12 months aft PCI.• 2. Periodic monitoring of selected, high-risk asymptomatic ps for

restenosis, graft occlusion, incomplete coronary revascularization, or disease progression.

Class III• 1. Localization of ischemia for determining the site of intervention.• 2. Routine, periodic monitoring of asymptomatic pts after PCI or CABG

without specific indications.

Investigation of Heart Rhythm Disorders

Class I• 1. Identification of appropriate settings in pts

with rate-adaptive pacemakers.• 2. Evaluation of cong CHB in pts considering

↑activity/competitive sports. (C)Class IIa• 1. Evaluating known or suspected exercise-

induced arrhythmias.• 2. Evaluation of medical, surgical, or ablative

therapy in exercise-induced arrhythmias

Investigation of Heart Rhythm Disorders

Class IIb• 1. Isolated VPC in middle-aged pts without

other evidence of CAD.• 2. Prolonged 1˚AV block or type I-2˚AV block ,

LBBB, RBBB, or VPC in young pts considering competitive sports. (C)

Class III• Routine investigation of isolated VPC in

young pts.

IN VALVULAR HEART DISEASE• Class1- c/c AR-Fun capacity & symp resp in

pats with equivocal sympt

• Class 2A c/c AR- FN capacity- athletic activity prog in c/c AR before AVR

Stress Testing

Modality Sensitivity Specificity

Exercise test 68% 77%

Nuclear Imaging 87-92% 80-85%

Stress Echo

80-85% 88-95%

EST RESPONSES & INTERPRETATIONS

Normal Response to Stress Testing• Heart rate increases

• Blood pressure increases

• Cardiac output increases

• Total peripheral resistance decreases

• Dysrhythmias – isolated unifocal PVC’s and PAC’s (suppressed at increased heart rate)

• Oxygen consumption increases

Abnormal Response to Stress Testing

• Heart rate fails to rise above 120 or unable to attain THR of 85% of max

• SBP shows a drop

• Physically unable to complete test

• Marked hypertension, >260/115

• Chest Pain and/or unusual shortness of breath

Normal Response of ECG to Stress Testing

• ECG Changes

– QRS complex ↓ in size– PR,QRS,QT shorten– J point ↓, resulting in up sloping of ST segment– ST segment returns to baseline by 80

milliseconds– PR segment may down slope(Inf leads– baseline

PQ junction)– R amplitude may decr at rates > 130– P ampl ↑– T wave decreases

The Electrocardiographic Response

1 = Iso-electric2 = J point3 = J + 80 msec

The Exercise ECG

• ST 60 -- HR > 130/min

• ST 80 -- HR ≤ 130/min

Criteria for Reading ST-Segment Changes on the Exercise ECG

ST DEPRESSION:

• Measurements made on 3 consecutive ECG complexes

• ST level is meas rel to the P-Q junction

• When J-point is dep rel to P-Q junction at baseline:

– Net diff from the rest J junction - amount of deviation

• When the J-point is ↑ rel to P-Q junction at baseline and becomes ↓ isoel with exercise:

– Mag of ST dep - P-Q junction and not the resting J point

Abnormal and Borderline ST-Segment Depression

• ABNORMAL:– 1.0 mm or > horizontal or downsloping ST dep at

80 msec after J point on 3 consecutive ECG complexes

• BORDERLINE:– 0.5 to 1.0 mm horizontal or downsloping ST dep at

80 msec after J point on 3 consecutive ECG complexes

– 1.5 mm or > upsloping ST dep at 80 msec after J

point on 3 consecutive ECG complexes

ECG changes during stress test

Normal

Rapid Upsloping

Minor ST Depression

Slow Upsloping

Horizontal

Downsloping

Elevation (non Q lead)

Elevation (Q wave lead)

ECG Patterns Indicative of Myocardial Ischaemia

ECG Patterns Not Indicative of Myocardial Ischaemia

• In lead V4 , the exercise ECG result is abnormal early in the test, reaching 0.3 mV (3 mm) of horizontal ST segment depression at the end of exercise.

• severe ischemic response.

•The J point at peak exertion is depressed 2.5 mm, the ST segment slope is 1.5 mV/sec, and the ST segment level at 80 msec after the J point is depressed 1.6 mm.

• “slow upsloping” ST segment at peak exercise indicates an ischemic pattern in patients with a high coronary disease prevalence pretest.

•typical ischemic pattern is seen at 3 minutes of the recovery phase when the ST segment is horizontal and 5 minutes after exertion when the ST segment is downsloping.

• abnormal at 9:30 minutes ES test and resolves in the immediate recovery phase.

•pattern in which the ST segment becomes abnormal only at high exercise workloads and returns to baseline in the immediate recovery phase may indicate a false-positive result in an asymptomatic individual without atherosclerotic risk factors.

ST ElevationAbnormal response

– J ↑ ≥0.10mV(1 mm)– ST 60 ≥0.10mV(1 mm)– Three consecutive beats

Q wave lead (Past MI)• Severe RWMA, ↓EF, ↓PrognosisNon Q wave lead (Past MI)• Severe ischemic response• Localise the culpritNon Q wave lead (No past MI)-1%• Transmural reversible myocardial ischemia-

----vasospasm, ↑coronary narrowing

•ST segment elevation in leads V2 and V3 with lesser degrees of ST segment elevation in leads V1 and V4 and J point depression with upsloping ST segments in lead II, associated with angina

•pattern is usually associated with a full-thickness, reversible myocardial perfusion defect in the corresponding left ventricular myocardial segments and high-grade intraluminal narrowing at coronary angiography

• coronary vasospasm produces this result in the absence of significant intraluminal atherosclerotic narrowing

Confounders of EST Interpretation• Digoxin

– abnormal ST-segment response to exercise.– occurs in 25% to 40% – directly related to age.

• LVH

– ↓ specificity of EST, sensitivity unaffected. – still the first test – Ab test- ref to add tests

• Resting ST ↓

– Resting ST-segment ↓ -even otherwise adverse

• LBBB– Ex-induced ST ↓ -no asso with ischemia

– no level of ST-seg dep - diag

• RBBB– do not ↓ sensitivity, specificity, or predictive value

• β- # THERAPY

– routine- unnecessary- to stop beta-blockers-† symp

– in patients taking -↓ diag & prog value - inadequate HRR

ERS and resting ST↑

• Return to the PQ Jn –nl

• ST↓ meas from PQ jn

• Not from the elevated J point before ex.

Duke Treadmill Score

Treadmill Score =

Ex.tme (min)

-5х (ST-seg dev in mm)- 4х ex.angina index

(0-no angina, 1 angina, 2 if angina stops test)

High Risk= -11, mortality - >5% annually

Low Risk= +5, mortality - 0.5% annually

DUKE TM SCORE

• Independent prog information

• =y good in males & females

• Not as effective in age≥ 75 yrs

ACC/AHA Guidelines:

high-risk test result- mortality ≥ 4%/yr→ for

cardiac cath

Intermediate-risk result -mortality 2- 3%/yr→

additional testing- cardiac cath, exercise

imaging study

Pseudo normalization pattern of T

• No prior MI Nondiagnostic finding

• Prior MI Sugg Reversible myocardial ischemia Needs - rev myo perfusion defect

R Wave amplitudeLVH Voltage criteria• ST seg – less reliable to ∆ CAD even in the

absence of LV strain pattern

Loss of R wave (MI)• ↓Sensitivity of ST response in that lead

U inversion

Occ in precordial leads at HR<120• Relatively insensitive but • Relatively specific 4 CAD

ST/HR SLOPE MAESUREMENTS• HR adj of ST seg dep-↑ sensitivity

• ST/HR slope of 2.4 mV/beats/min-abnormal

• >6mV/beats/min -3 vessel disease

• CORNELL protocol-gradual inc in HR

• ST seg/HR index-av change of ST dep with HR through out the course of ex test

• > 1.6 -abnormal

Abnormal BP Response• Failure to ↑SBP >120 mmHg

• Sustained ↓(15 secs) >10mmHg

• ↓SBP below resting BP during progressive exe• Inadequate ↑ of CO

• Hypo episode 3- 9% of symp pats Extensive CAD & perfusion defects LMCA/ 3 VD

Exercise CapacityVO max = (mph x 26.8) x (0.1 + [% grade X 1.8] + 3.5

Stage 1 = 5 METS

Stage 2 = 6 - 8 METS

Stage 3 = 8 -10 METS

2

2

1-MET ↑in exercise capacity, the survival improved by 12 % N Engl J Med 2002

Heart rate response Chronotropic incompetence-adv prog• Inability to attain THR OR• Ab HRR (<80%)

{%HR Reserve=(HRpeak-HRrest)/(220-age- HRrest)} Chronotropic index• ANS dysfunction,SN dysfuntion, drugs,

myocardial ischemia• ↑long term mortality-< 80%CI (not on β

blockers)

Heart Rate Recovery

-Rapid reactivation of vagal tone - ↓ in heart rate post ex- nl

-Slow decceleration post ex

-↓ vagal tone

HRR=HR (peak)-HR (1 min later)

TMT (upright) < 12 bpm

TMT (supine) < 18 bpm

upright value <22 bpm at 2 minutes is abnormal

Prognostic power independent of other factors

HRR Predicts Outcome in CAD

Exercise induced Chest discomfort• Usually after ischemic ST changes• +/-↑DBP• chest discomfort –only sgn of CAD

• In CSA, CP less freq than ST↓Angina with no ST ↓- MPI to assess ischemic

severity.

(+) Stress Test with angina → 5%/yr.( mortality)

(+) Stress Test, no angina → 2.5%/yr.

Adverse prognosis & multivessel CAD• Symptom limiting exercise < 5METs

• Abnormal BP response

• ST↓ ≥2mm or downsloping ST↓→ <5METs, ≥5 leads, persisting ≥5 mins into recovery

• ST↑( except aVR)

• Angina at low exercise work loads

• Reproducible sustained/symptomatic VT

Indications for Terminating Exercise Testing

Absolute indications• ↓ SBP >10 mm Hg fm baseline +other evidence of

ischemia• Mod - severe angina• ↑ CNS sympts (ataxia, dizziness, or near-syncope)• Signs of poor perfusion (cyanosis or pallor)• Technical diff in monitoring ECG or systolic BP• Subject’s desire to stop• Sustained VT• ST ↑ (≥1.0 mm) in leads without Q-waves (other

than V1 or aVR)

Relative indications• ↓ in S BP (≥10 mm Hg) in the absence of other

evidence of ischemia• ST or QRS changes - excessive ST↓ (>2 mm of

horizontal or downsloping ST↓ ) or marked axis shift• Arrhythmias other than sustained VT, including

multifocal PVCs, triplets of PVCs, SVT, heart block, or bradyarrhythmias

• Fatigue, shortness of breath, wheezing, leg cramps, or claudication

• Devp of BBB or IVCD that cannot be distinguished from VT

• Increasing chest pain• Hypertensive response(250/115 mm hg)

Sub maximal ex test• Signs & sympt of ischemia

• Att of a work load of 6 METS

• 85% of APMHR

• HR of 110 beats / min –on β blockers

• BORG score 17

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