STRESS TEST

(aka Excercise Electrocardiography)

Why is it done? Excercise shows heart dysfunction not apparent at rest.

Composed of 4 stages: (Stage 1 - Stage 4)

Done as either a

• (1) DIAGNOSTIC test.
• > 5 days post MI
• Stable Angina
• (2) PROGNOSTIC test
• If currently on meds for angina, etc, and want to know the effect.

Whenever performing a Stress Test, you must have the following:

• 12 lead ECG
• Resuscitation Equipment i.e. Cardiac Arrest Kit
• Adrenaline, Atropine, Lignocaine
• Increasing workload option available on a bicycle or a treadmill

How is it performed:

• Bruce Protocol (the main protocol): 3 minute stages x 4 stages. Each stage you increase the belt speed and treadmill gradient
• Modified Bruce Protocol, Naughton, Ellestad all of which use variations of smaller increments in workload, shorter duration, and less elevation of the treadmill.
• Maximum heart rate is determined by: 220 - age
• A HR should increase about 10 bpm/stage ( a delay is noted in athletes and patients taking B blockers)
• BP should increase 10 mmHg/stage (delay in athletes)
• Sensitivity and Specificity of Stress Test is 65% and 65%
• Causes of false positives in Stress Test are: Female, Hyperventilation, Mitral valve prolapse, Left Vent Hypertrophy, Digitalis.

Stress Test Contraindications:

• Unstable Angina
• Hypertrophic Obstructive CardioMyopathy (HOCM)
• Decompensated CHF
• Severe subaortic stenosis
• Uncontrolled arrhythmia or heartblock
• Inability to walk on treadmill due to neurologic or musculoskeletal abnormalities or to vascular disease
• Acute myocarditis or pericarditis
• Acute systemic illness
• Malignant Hypertension
• < 5 days post-MI

Stop the Test when the patient gets:

• Chest pain, Lightheaded or Short of breath (all these are symptoms of ischaemia)
• ECG abnormalities (there are 3 possible ECG findings):
• ST depression > 2mm = ischaemia (high false positive rate of ST depression (20%)
• ST elevation > 2mm = infarction
• VTAC - ventricular tachycardia (remember that the coronary arteries fill and vascularize the myocardium in diastole, so if systole is occupying most of the cardiac cycle, ischaemia sets in)
• BP abnormalities
• absent hypertensive response (no increase in BP with stress, which should happen in normals)
• paradoxical decrease in BP
• note: BP = TPR x CO, so TPR increases with adrenaline, and CO should increase as well because of the Frank-Starling model of pre-load, but since ischaemia is present, the myocardium does not function accordingly and so CO remains the same, or even decreases, thus causing a sustained resting BP or a paradoxical decrease in BP.
• BP is also checked after the stress test, to see if it is the same as the BP taken before the stress test. If it is the same, or lower, then it is a positive finding therefore = Positive Stress Test.

If all is well, and the patient has coped normally with the stress test, this is called a Negative Stress Test. And this denotes an excellent prognosis.

If Positive Stress Test, must mention time, i.e. Developed ECG changes @ 5 minutes on treadmill:

• Angiography: if only a low workload is achieved before important abnormalities occur
• Medical treatment of angina may be appropriate if three or four stages are completed before abnormalities appear.

Alternatives to excercise test?

• Dobutamine testing with radionuclide perfusion scan.
• c/i:
• Asthma, COPD, recent CVA
• Caffeine and theophylline must be witheld before testing.
• Dipyridamole (DP) testing with radiocuclide perfusion scan
• c/i
• sig HTN, and known catechol induce arrhythmias
• Some centers are evaluating adenosine infusions
• The indications for these pharmacological testings are the same as for the excercise test, except that it caters for patients who cannot excercise due to musculoskeletal disease, neurologic disease, or vascular disease.
• It does not, however, give information on functional status or the efficacy of antianginal therapy.