Exercise ECG: The stress test on the Treadmill

Sangeetha.K

Cardiac Technician, Kauvery Hospital Heart City, Trichy, Tamil Nadu, Trichy.

Background

Dr. Robert A. Bruce, who was born in the Boston suburb of Somerville on 20 November 1916, is considered the father of exercise physiology and devised the well-known Bruce protocol for the Treadmill Test. Published as a standardized protocol in 1963. Gold standard for detection of myocardial ischemia when risk stratification is necessary.

Treadmill Testing

  1. Treadmill testing is a non-invasive tool to evaluate the cardiovascular systems response to exercise.
  2. Exercise is the body’s most common physiologic stress, and it places major demands on the cardiopulmonary system.
  3. Thus, exercise can be considered the most practical test of cardiac perfusion and function.
  4. Body can increase its resting metabolic rate up to 20 times, cardiac output upto 6 times.
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Alternative names

  1. Exercise ECG,
  2. ECG – Exercise treadmill,
  3. EKG – Exercise Treadmill,
  4. Stress ECG,
  5. Exercise electrocardiography,
  6. Stress test – exercise tread mill.

Definition

It is used to estimate the prognosis and to determine functional capacity, the likelihood and extent of CAD and effects of therapy. Treadmill test is also called a stress test, exercise electrocardiogram, graded exercise test or stress ECG, it is used to provide information about how the heart responds to exertion. It usually involves walking on a treadmill at increasing levels of difficulty, while electrocardiogram, heart rate and blood pressure are monitored.

Measurements

  1. Electrocardiogram (ECG)
  2. Exercise capacity (METS – metabolic equivalent)
  3. Symptoms
  4. Blood pressure
  5. Heart rate response & recovery
  6. ST – segment abnormalities and chest pain
  7. The patient should be monitored continuously

Pre Procedure Care

General concerns prior to performing an exercise test include,

  1. Patients should be instructed not to drink, eat caffeinated beverages or smoke 3 hr before testing and to wear comfortable shoes and clothes
  2. Unusual physical exertion should be avoided
  3. Brief history and physical examination should be performed
  4. Should be instructed about risks and benefits
  5. Informed consent is taken.
  6. Area of electrode application should be rubbed with alcohol saturated pad to remove oil and rubbed with sand paper to reduce skin resistance to 5000 ohms or less
  7. Cables should be light flexible and shielded
  8. Room temp should be 18 – 24°C and humidity less than 60%
  9. IV line should be started in high risk patients
  10. Safety precautions and equipment needs:
  1. Everything necessary for cardiopulmonary resuscitation must be available and regular drills should be performed to ascertain that both personnel and equipment are ready for a cardiac emergency.
  2. The treadmill should have front and side rails for subjects to steady themselves.
  3. A resuscitation cart, defibrillator and appropriate cardio active drugs should be available in the TMT room.

Method of doing TMT

During the test, you will be asked to exercise typically on a treadmill while you are hooked up to an ECG machine. This allows your doctor to monitor your Heart rate

THR=220-age

Duke Treadmill Test

  1. Exercise time or Phase time: Treadmill Exercise test
  2. Max ST: Max net ST Elevation [Except aVR]
  3. Angina Index: Treadmill Angina Index
  • 0 – No angina during exercise
  • 1 – Non limiting angina
  • 2 – Exercise limiting angina
  1. DTS = Exercise time – [5 × max ST] – [4 × angina index]

Duke Treadmill Score

  1. 5 – Low Risk
  2. 410 – Moderate Risk
  3. ≤ 11 – High Risk.

Indication

  1. Symptoms suggesting angina
  2. New heart Failure
  3. Known CHD and change in clinical status
  4. Evaluate the presence of arrhythmia due to CAD
  5. Valvular heart disease
  6. Undergoing non urgent and non cardiac surgery
  7. Age: minimum 18 years/maximum 75 years
  8. Master health check-ups.

Contraindications

  1. Myopericarditis
  2. Severe Aortic Stenosis
  3. Uncontrolled hypertension
  4. Acute phase of MI
  5. Aortic Dissection
  6. Unstable Angina (3 days)
  7. Arrhythmia (mainly LBBB)
  8. Fever/Acute viral illness
  9. Decompensated heart failures
  10. Uncooperative patients
  11. Acute Pulmonary Embolism
  12. Hypertrophic cardiomyopathy

ECG effects of impaired coronary blood flow may be reflected by (or) Interpretation of TMT

  1. Abnormalities of the repolarization
  2. Abnormalities of the depolarization
  3. The Abnormal QRS – T angle
  4. Abnormal manifestation of the repolarization
  5. Abnormalities of the ST segment, T and U wave
  6. Changes occurs in QT interval.

Treadmill protocols

  1. Bruce
  2. Modified Bruce
  3. Cornel
  4. Ramp Protocol
  5. Balke-Ware
  6. Naughton and Weber
  7. ACIP (Asymptomatic Cardiac Ischemia Pilot)
  8. Modified ACIP
  9. Among this protocols, the two main and widely accepted protocols for doing TMT are:
  10. Bruce Protocol
  11. Modified Bruce Protocol.

Bruce Protocol

  1. The Bruce protocol is a standard test in cardiology
  2. It is comprised of multiple exercise stages of three minutes each.
  3. At each stage, the gradient and speed of the treadmill
  4. TMT are elevated to increase work output called METS
  5. Stage 1 of the Bruce protocol is performed at 1.7 miles per hour and a 10% gradient.

Stage

Minutes

Slope (%)

MPH

METS
1 3 10 1.7 5
2 6 12 2.5 7
3 9 14 3.4 10
4 12 16 4.2 13
5 15 18 5.0 15
6 18 20 5.5 18
7 21 22 6.0 20

Modified Bruce Protocols

  1. Starts at a lower workload than the standard test
  2. Typically used for elderly or sedentary patients
  3. The first two stages of the Modified Bruce Test are performed at a 1.7 mph and 0% grade and 1.7 mph 5% grade
  4. The third stage corresponds to the first stage of the Standard Bruce Test protocol

Stage

Minutes

Slope (%)

MPH

METS
0 3 0 1.7 2.9
0.5 3 5 1.7 3.7
1 3 10 1.7 5.1
2 3 12 2.5 7.1
3 3 14 3.4 10.3
4 3 16 4.2 13.1
5 3 18 5.0 16

 

Metabolic Equivalents
1 MET Resting
2 METS Level walking at 2 mph
4METS 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
13 METS Excellent prognosis regardless of other exercise responses
18 METS Elite endurance athletes
20 METS World class athletes

ST Segment

The ST Segment represents the interval between ventricular depolarization and repolarization. Abnormal ST Segment

  1. ST segment elevation
  2. ST segment depression

Cause: Myocardial ischemia or infarction.

ST Segment Elevation

  1. ST-Elevation Myocardial Infarction (STEMI) is a very serious type ofheartattack during which one of theheart’smajor arteries is blocked.
  2. ST segment elevation is a good indicator of severe ischemia and poor collateral circulation.
  3. Several other case reports also found rare cases of ST elevations in non-Q wave leads during exercise stress testing that accurately predicted the presence of coronary stenosis.
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ST Segment Depression

  1. ST depressionoccurs when the J point is displaced below baseline.
  2. Just likeST elevation, not allST depressionrepresents myocardial ischemia or an emergent condition.
  3. There are multiple conditions associated withST depression.
  4. Some of these include hypokalemia, cardiac ischemia, and medications such as digitalis.
  5. The commonest abnormalities of the ST segment depression is markedly seen in lead V5, V6, II and III.

Types of ST Segment Depression

  1. Junctional ST segment depression
  2. Upward ST segment depression
  3. Horizontal ST .Segment depression
  4. Plain ST segment depression
  5. Sagging ST segment depression
  6. Downward ST segment depression.
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Junctional ST Segment Depression

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Coronary Causes of ST Segment Depression

  1. Severe aortic stenosis
  2. Severe hypertension
  3. Cardiomyopathy
  4. Anemia
  5. Hypokalemia
  6. Severe hypoxia
  7. Sudden excessive exercise.

Non Coronary Causes of ST Segment Depression

  1. Glucose load
  2. Left ventricular hypertrophy
  3. Hyperventilation
  4. Mitral valve prolapsed
  5. Pre excitation syndrome
  6. Supraventricular tachyarrhythmias
  7. Interventricular conduction disturbance.

Abnormalities of the T wave

  1. Normal T wave – Asymmetrical
  2. Abnormal T wave – Symmetrical
  3. Peaked T wave
  4. Inverted T wave
  5. Biphasic T wave
  6. Flattened T wave
  7. Hyper acute T wave
  8. ‘Camel hump’ T wave.

Peaked T Waves

Tall, narrow, symmetrically peaked T-waves are characteristically seen inhyperkalemia.

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Inverted T wave

  1. Inverted T wave is considered abnormal
  2. If inversion is deeper than 1.0 mm.
  3. Inverted T waves found in leads other
  4. Than the V1 to V4 leads is associated with increased cardiac deaths.
  5. Inverted T waves associated with cardiac signs and symptoms (chest painandcardiac murmur) are highly suggestive of myocardial ischemia
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Biphasic T Wave

Move in opposite directions.

Main causes: myocardial ischemia, hypokalemia

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Flattened T wave

T wave is considered flat when the wave varies from -1.0mm to + 1.0mm in height

Causes: Hypokalemia, Digitalis therapy

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Hyperacute T wave

Seen in patients displaying Prinzmetal angina.

Patients exhibiting the early stages of STEMI may display these broad and disproportional waves

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CAMEL HUMP’ T Wave

  1. The shape it exhibits (double peaks).
  2. Causes
  3. Hypothermia
  4. Severe brain damage
  5. Several conditions, including electrolyte imbalance

U Wave

  1. The U wave is a small (0.5 mm) deflection immediately following the T wave
  2. U wave is usually in the same direction as the T wave.
  3. U wave is best seen in leads V2 and V3.
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Causes of inverted U waves

  1. Coronary artery disease
  2. Hypertension
  3. Valvular heart disease
  4. Congenital heart disease
  5. Cardiomyopathy
  6. Hyperthyroidism

Negative

  1. No change
  2. ST depression doesnt fulfill no.2
  3. T wave inversion w/o ST segment changes
  4. ST elevation in a Q wave lead
  5. Target heart rate (85% of maximal predicted heart for age and sex) is not achieved

ST depression

  1. A flat or down sloping depression of the ST segment > 0.1 mV below baseline the PR segment and lasting longer than 0.08s.
  2. Up sloping or junctional ST segment changes are not considered characteristic of ischemia and do not constitute a positive test.

ST Elevation: 1 mm at 60 msec

 

Strongly Positive 5 Rules

  1. 5 mm of ST depression
  2. ST depression persistent > 5 min recovery
  3. 5 leads ST depression was seen
  4. < 5 min of walk
  5. < 5 min changes

Recovery after exercise

  1. If maximal sensitivity is to be achieved with an exercise test, patients should be supine as soon as possible during the post exercise period (maximal wall stress)
  2. A cool-down walk can be helpful in performing tests on patients with an established diagnosis undergoing testing for other than diagnostic reasons in testing athletes or patients with congestive heart failure (CHF), valvular heart disease, or a recent (MI).
  3. A cool-down walk after the test can delay or eliminate the appearance of ST-segment depression.
  4. Monitoring should continue for at least 5 minutes after exercise or until changes stabilize.

Complications

These are rare but can be fatal; myocardial infarction, left ventricular rupture, ventricular fibrillation or ventricular tachycardia.

Conclusion

  1. The exercise test continues to have an integral place in cardiovascular medicine because of its yield of diagnostic, prognostic and functional information.
  2. In the clinical setting, the major indications for exercise testing are the diagnosis and prognostication of heart disease. The determination of exercise capacity is helpful in quantifying disability, estimating prognosis and monitoring the disease state of patients with chronic heart disease and known coronary heart disease.

References

  1. Libby P. bonow RO, Mann DL, Zipes DP.Exercise stress testing. braunwald E, ed . braunwalds heart disease: A textbook of cardiovascular medicine. 8 th ed, Philadelphia . pa:WB saunders. 2007.
  2. Botvinick EH. current methods of pharmacologic stress testing and the potential advantages of new agents. J Nucl Med Technol. 2009 Mar. 37 (1) : 14-25.
  3. Feil H, Siegel ML. Electrocardiographic changes during attacks of angina pectoris. Am J Med sci. 1928;175:255

Michael W. Luong, Maya Ignaszewski, C.M. Taylor. Stress testing: A contribution from Dr Robert A. Bruce, father of exercise cardiology. BCMJ. 2016;58(2):70-76

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Sangeetha.K

Cardiac Technician

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