Fig. 4.1
The ischemic cascade: represent the magnitude of ischemia in relation to the increasing duration of ischemia. The initial changes seen are perfusion abnormalities detected with nuclear myocardial perfusion imaging. With increasing ischemia, diastolic dysfunction followed by systolic dysfunction occurs. At this stage, wall motion abnormalities (WMA) are detected by stress echocardiography. It is only at the late stages, that ECG changes and angina develops
There is two types of exercise stress tests that can be performed: bicycle and treadmill with the latter being the most widely used in the US. The advantages that bicycle ergometry have over treadmill is the ability to be performed in patients with weight bearing problems, patients with gait/balance and orthopedic abnormalities, a cleaner (less noise) ECG for interpretation, and the ability to take direct measurements of workload in watts which has a linear relationship with myocardial oxygen consumption (MVO2).
Indications
The most common indications according to the 2002 ACC/AHA guidelines for exercise testing and the 2014 guidelines for stable ischemic heart disease [1–3] are (Table 4.1).
Table 4.1
Indications for exercise ECG stress testing
1. | Symptoms suggestive of CAD |
2. | Acute chest pain after ACS is ruled out |
3. | Recent ACS not treated with coronary angioplasty |
4. | Known CAD and change in clinical status |
5. | Prior incomplete revascularization |
6. | Valvular heart disease |
7. | Newly diagnosed cardiomyopathy |
8. | Certain cardiac arrhythmias |
9. | Pre-op cardiac assessment prior to non-cardiac surgery |
Most commonly, ET is used in the diagnosis of ischemic heart disease in patients with intermediate pretest probability of CAD and/or risk stratification of patients with intermediate or high pretest probability of CAD based on age, gender, and symptoms (Table 4.2).
Table 4.2
Pretest probability of CAD
Age (year) | Gender | Typical/definite angina | Atypical/probable angina | Non-anginal 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 |
There are several conditions in which exercise tests should be combined with an imaging modality; either myocardial perfusion imaging (MPI-SPECT or PET) or echocardiography. These conditions include: ventricular paced rhythm, left bundle branch block (LBBB), pre-excitation (Wolff-Parkinson-White syndrome), >1 mm ST depression at rest, patients taking digoxin, previous PCI/CABG, left ventricular hypertrophy (LVH), and right bundle branch block (RBBB) which precludes ST segment interpretation in leads V1–3.
ET may also be used for patients with valvular heart disease (such as mitral stenosis, aortic stenosis, and aortic regurgitation) to assess for symptoms; this is usually performed in conjunction with echocardiography.
Contraindications (Table 4.3)
Absolute contraindications to exercise stress testing |
Acute myocardial infarction (within 2 days) |
High risk unstable angina |
Uncontrolled cardiac arrhythmias |
Symptomatic severe aortic stenosis |
Uncontrolled symptomatic heart failure |
Acute pulmonary embolus or pulmonary infarction |
Acute myocarditis or pericarditis |
Acute aortic dissection |
Relative contraindications to exercise stress testing |
Left main coronary stenosis or it’s equivalent |
Moderate stenotic valvular heart disease |
Electrolyte abnormalities |
Severe arterial hypertension |
Tachyarrhythmias or bradyarrhythmias |
Hypertrophic cardiomyopathy and other forms of outflow tract obstruction |
Mental or physical impairment leading to inability to exercise adequately |
High degree atrioventricular block |
Equipment
The equipment for a treadmill ECG stress test includes the treadmill, ECG electrodes, BP cuff, and the recording computer system that controls the stress testing protocol being used. In addition, a physician or physician assistant/nurse practitioner should supervise the test (with a physician on site). The exercise protocols in practice are the Bruce protocol, Modified Bruce protocol, Naughton, Blake, and Cornell protocols. Each varies according to the speed and grade parameters. The Bruce protocol is the most widely used and validated; the protocol is divided into 3-min stages that increase in speed and inclination (Table 4.4).
Table 4.4
Bruce protocol
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