Load
(watts)
Duration
(min)
Peak estimated METs
Designation
Start
Increase
Peak
Stage
Total
Balke (men)
50
25
175
2
12
9.5
Balke (women)
25
25
150
2
12
8.3
Astrand
25
25
150
3
18
8.3
Designation | Estimated METs | ||
|---|---|---|---|
At 8 min | At 9 min | At 12 min | |
Naughton | 4 | NA | 6 |
Balke-Warea | 5 | NA | 8 |
Modified Bruce | NA | 7 | 10 |
Bruce | NA | 10 | 13 |
1.4 When to Do It
The ET must be performed at the admission of the CRP in the majority of program participants, sometimes in the middle of a phase when it seems that the patient’s clinical status changed or THR is inadequate due to the acquisition of a better exercise tolerance as a consequence of exercise training and at the end of each phase to measure the final functional capacity [2, 4, 16].
Patients recently submitted to cardiac surgery are usually admitted in the CRP, without performing an ET, because they may face physical limitations that advise to postpone the test for 2–4 weeks. During these early weeks, the patients are involved in respiratory and global physiotherapy and may even start exercising in a stationary bike or on the treadmill, below a THR of 100 or 120, respectively, if they are or not under β-blocker medication, till they reach a satisfactory exercise tolerance that enables them to be submitted to the ET, after what an individualized THR will be calculated [2].
1.5 How to Report the ET in the Setting of a CRP
A standard ET must be reported not only in terms of the presence or absence of myocardial ischemia but also about enlightening the global prognosis, as it is shown in the Table 1.3.
1. Exercise capacity |
(a) Test duration and reason to stop the exercise |
(b) In a classical ET, estimate exercise tolerance, as ratio between the achieved and the predicted METs, calculated by the following equations: |
(i) Men: Predicted METs = 14.7–0.11 × age |
(ii) Women: Predicted METs = 14.7–0.13 × age |
(c) In a CPX, measure exercise tolerance and use Weber classification and percentage of predicted VO2 max |
Classify functional capacity below normal if lower than 85 % of the predicted value |
2. Heart rate |
HR at rest, at the end of each stage, at the moment of the ischemic threshold, ventricular or supraventricular arrhythmias starting, abnormal BP (drop or hypertensive response) at peak exercise and in recovery at 1, 3, and 6 min |
Classify chronotropic evolution during exercise as: |
Normal, if peak HR value is above 85 % of the predicted value (220 bpm minus age), for individuals not under β-blocker or above 62 % under β-blocker |
Abnormal, if below the mentioned values |
Classify chronotropic evolution during recovery as |
Normal, if HR difference between peak exercise and min 1 > 12 on protocols where there is an active recovery (slow walking or pedaling) or >18 bpm, if exercise is immediately stopped at peak effort |
Abnormal, if below the mentioned values |
3. Blood pressure |
Classify blood pressure evolution as |
Normal, if SBP increases ~10 mmHg per MET and there is no change or a small drop is found in DBP. It’s acceptable to find a drop <15 mmHg at peak exercise |
Hypertensive, if SBP reaches values >250 or >DBP 120 mmHg |
Insufficient, if SBP increases <30 mmHg |
4. Ischemia |
Classify the test as negative, positive, equivocal, or inconclusive for myocardial ischemia, taking into consideration the presence or absence of angina or ST depression/elevation induced during the test, in the exercise or the recovery period, according to the criteria defined in the guidelines |
Use the ST/HR index, the ST rate-recovery loops, and/or the ST/HR slope to increase the accuracy of the diagnosis of ischemia |
Grade ischemia as severe, moderate, or low level, taking into consideration the precocity of appearance, magnitude of ST changes, time until normalization in the recovery period, association with limiting angina, BP fall, chronotropic deficit, or ventricular arrhythmias |
Identify clearly the HR of the ischemic threshold, because the THR to be observed during the exercise sessions must be 10 bpm below this value for safety reasons |
5. Prognosis |
Assess globally the prognosis, considering functional capacity, ST/HR index, chronotropic response, HR recovery, ventricular ectopy during recovery, and ST/HR slope, which are implicated in global and cardiovascular mortality and events |
6. Aerobic training intensity |
Classically, THR is calculated as the HR at (50), 60–70 % of HR reserve or (50), or the HR reached at 60–70 % of VO2 reserve or at HR of the VAT level, respectively, if the patient was submitted to a standard ET or to a CPX [16] |
More recently, important changes in terms of determination of THR occurred, due to the adoption of new modalities of exercise training like high-intensity exercise training (HIIT) and to the change of concept of the submaximal exercise thresholds. Today, the concept of only one threshold, previously called ventilatory anaerobic threshold (VAT), was abandoned, and it was adopted the concept of two submaximal thresholds, the first and the second ventilatory thresholds identified, respectively, by the nadir of the curves of the O2 and VCO2 equivalents [14, 15] |
In the case of continuous moderate aerobic training, exercise training must start at the level of HR attained by the subject at the level of the first ventilatory threshold (LVT1) and move till the HR attained at the level of the second ventilatory (LVT2) |
After the seminal paper of Wisloff [28] and coworkers, a new paradigm emerged: HIIT. In this case, exercise intensity is prescribed at up to 95 % of HR attained during the ET for periods of 4 min, intercalated by 3 min periods of not so intense training at 50–75 % of peak exercise |
The test must be reported not only in terms of myocardial ischemia but also on functional capacity, chronotropic index, HR recovery, BP, and ventricular or supraventricular arrhythmias.
Despite having informed the patient at the beginning of the ET about the need to spontaneously report the occurrence of any unexpected symptom, namely, angina or a disproportionate grade of dyspnea or fatigue, it’s also advised to ask periodically, for example, at the end of each stage and at the moment of ST depression occurrence, if the patient is experiencing angina and what is his perception of exercise intensity (Borg scale). During the exercise period, it is also recommended to record every minute a full ECG in order to define accurately the eventual moment after which ST segment depression reaches 1 mm and 60 or 80 ms after the J point, the so-called ischemic threshold.
Ischemia is diagnosed by the occurrence of angina and/or definitive ST changes on the exercise or in the recovery period. In order to increase the diagnostic accuracy of the ET, ST changes must be interpreted considering ST/HR index, which must be superior to 1.6 μV/bpm, and rate-recovery loops that are suggestive of myocardial ischemia if there is a counterclockwise rate-recovery loop.
Functional capacity is probably the most important finding after an ET as it is the best parameter to predict all-cause mortality. When peak VO2 is not measured, it can be estimated by the ratio between the estimated METs achieved at the last stage of the ET and the predicted value given by the following formula: Predicted METs = 14.7–0.11 × age or 14.7–0.13 × age, respectively, for men and women. To allocate the estimated METs of a stage, the patients must exercise at least 1 min at that stage. If he was not able to do it, his maximal METs attained will be the ones estimated for the previous completed stage.
The Duke score tries to put together the presence/absence of ischemia and functional capacity and classifies the patients in low, intermediate, and high categories of risk, according to the value of the score.
Chronotropic index, HR recovery, and ventricular arrhythmias predict increased/decreased risk of death if they are negative or positive.
1.6 How to Assess Exercise Training with a Standard ET or a CPX
At the end of a CRP phase, the ET or the CPX must be repeated to be compared with the test performed at the phase start, in order to document eventual gains provided by the program.
These gains must be observed in terms of maximal and submaximal functional capacity, ischemic threshold, exercise-induced or exercise-worsened arrhythmias, heart rate, and blood pressure evolution during the exercise and the recovery periods [2, 6, 16].
To make a correct comparison between both tests, they must be performed under the same medication, at the same time of the day, and using the same ergometer and protocol. If any revascularization procedure, like a PCI, is performed, the medication is changed between the tests, or if the ergometer or the protocols are also different, a direct comparison of both tests is impossible.
1.6.1 Standard ET
If exercise training is successful, the standard ET will usually show in the second test:
- (a)
Higher duration/load attained
- (b)
Lower levels of HR and BP at each stage and an early normalization of HR during recovery
- (c)
Starting of ischemia later during the test, although at the same or higher double product
- (d)
Lower frequency and complexity of ventricular arrhythmias, in the exercise or recovery periods
Functional capacity can be estimated for each patient in terms of METs (metabolic units of oxygen consumption: 1 MET = 3.5 ml/kg/min) considering the oxygen consumption previously known to be inherent to the highest stage attained at peak exercise, if the patient was able to keep this stage more than 1 min. If the test was stopped before staying 1 min or more in the last stage, the attributed estimated METS must be those predicted for the previous completed, since usually it takes, at least, 1 min to stabilize oxygen consumption in each exercise protocol stage.
Functional capacity must also be classified regarding the predicted values for the same age, gender, and physical activity status, provided by several equations.
The maximal load reached by the patients can also be considered as a measure of functional capacity, especially when a stationary bike is used. In a treadmill, due to the body weight dislocation effect and the walking, the peak load values are less accurate.
The estimation of aerobic capacity by the standard ET is not very accurate, since it usually overestimates the load, namely, in the case of patients and old people and when treadmill protocols with high increment protocols are used, like the Bruce protocol.
1.6.2 Cardiopulmonary Exercise Test
The CPX allows the best identification of maximal aerobic capacity because peak VO2, the gold standard for exercise capacity, is directly measured “breath by breath” during the entire test. Due to some variability, the values should be determined by calculating the rolling average of each period of 20–30 s [29].
Peak VO2 is the most used parameter to evaluate the CRP benefit. In case of doubt that the CPX is a maximal test, one must specially look at VO2, HR, and respiratory exchange ratio (RER) and RPE at peak exercise level. VO2 and/or HR must fail to increase significantly despite load further increments; RER and RPE must be, respectively, equal or over 1.10 and 8/10 at peak [30].
Recently, the terminology of the events observed at submaximal level during a CPX was changed. Now, two thresholds are recognized instead of the only one, the formerly designed ventilatory anaerobic threshold (VAT), presently called the first VT (VT1). Also, the formerly designated respiratory compensation point is called now the second ventilatory threshold. These thresholds are defined, respectively, as the nadir points of the curves of the O2 and CO2 equivalents, which have a U shape form during the exercise period. These equivalents are, respectively, the ratios of O2 and CO2/ventilation [14, 15].
VT1, formerly designated by VAT, can also be calculated by the V slope method and defines the end of the period where exercise intensity is not perceived by the individual as difficult to be performed. Between VT1 and VT2, exercise intensity is perceived as moderate and after surpassing VT2 as very intense and difficult to maintain for a few minutes.
To overcome the limitations of peak VO2, the VO2 attained at the VT1 can be used to evaluate the training effect, because it is independent of patient motivation and expresses better the patient capacity to perform daily life activities.
In cardiac patients, peak VO2 and VO2 at the VT1 increase between 7 and 54 % after a period of some weeks of exercise training, although the average increase is usually around 20–30 % [31–33].
VE/VCO2 slope, which evaluates ventilatory efficiency, one of the most important parameters for prognosis assessment in CHF, is also expected to decrease as a demonstration of a favorable exercise training period (Table 1.4) [34, 36].
Standard ET | Cardiopulmonary exercise test |
|---|---|
Test duration, maximal load, and estimated METs | The same parameters as in standard ET, plus: |
Presence or absence of ischemia | Peak VO2 |
HR at rest, at each stage, at peak exercise, and on recovery | VO2 and HR at VAT |
Blood pressure at rest, at each stage, at peak exercise, and on recovery | O2 kinetics in the recovery period |
Ischemic threshold: HR, double product, and load | Peak RER |
Grade of myocardial ischemia, in terms of ST normalization, ST depression morphology | VE and breathing reserve |
Ventricular arrhythmias | VE/VCO2 slope |
Compare pre- and post-exercise tests, performed at the same time of the day, under the same medication and protocol.
1.7 Clinical Cases
Case #1
Male, 41 years old
Apparently healthy till 20th of April 2009 when he suffered an anterior myocardial infarction. Tobacco smoking, obesity, and psychological stress were identified as risk factors for CVD in this case: he smoked one pack a day during 25 years and has a BMI of 30.6 (99 kg of weight and 180 cm height). His BP, blood cholesterol, and glucose levels were normal.
He was submitted to primary PCI of LAD (middle portion) that was totally occluded by a thrombus. The PCI was performed within 2 h of symptoms and was very successful, with the exception of the occurrence of a right thigh hematoma related to the femoral puncture, which obliged him to rest in bed for a week. No other lesions were found in the coronary arteries, and LV function was near normal.
He was discharged from the hospital on the fifth day after ACS under ASA, clopidogrel, ramipril (2.5 mg, od), bisoprolol (2.5 mg, od), and pravastatin (40 mg, od).
When he started to go out of bed and to move around 1 week after hospital discharge, he felt dizziness, nausea, and a thoracic discomfort, different from the one that arose during the ACS, which stopped immediately when he lay down. No pericardial effusion was found on echocardiography. After this he took the initiative to contact our CRP 3 weeks after the ACS.
After a medical consultation and physical examination, where everything seemed to be OK, he was submitted to an ET (Table 1.5; Fig. 1.1).
Table 1.5
Exercise test parameters (case #1)
Stage | Speed km/h | Grade % | METs | HR bpm | SBP mmHg | DBP mmHg | Symptoms | ECG |
|---|---|---|---|---|---|---|---|---|
Rest | 0 | 0 | 1 | 75 | 130 | 80 | No | T wave inversion V1-V4 |
I | 2.7 | 10 | 4.6 | 98 | 150 | 80 | No | Almost normal |
II | 4.0 | 12 | 7.0 | 117 | 175 | 90 | Mild fatigue | Normal |
III | 5.4 | 14 | 10.0 | 138 | 200 | 100 | Moderate fatigue | Normal |
IV | 6.7 | 16 | 12.5 | 150 | 210 | 100 | Severe fatigue | Normal |
Exercise duration: 10 min 20 s | ||||||||
Rec. 1’ | 1.5 | 0 | 132 | 200 | 90 | No | Normal | |
Rec. 3’ | 0 | 0 | 104 | 190 | 90 | No | Normal | |
Rec. 6’ | 0 | 0 | 95 | 170 | 85 | No | Normal | |
Fig. 1.1
Rest and peak exercise 12-lead ECG (case #1)
Comments ET#1
Confronting the findings of this ET with what is supposed to be found in a normal ET, this patient shows:
- 1.
Good exercise tolerance: 10–20 min exercise duration on the Bruce protocol ~12.5 METs (122 % of the predicted).
- 2.
Normal evolution of HR: from 75 to 150 bpm at peak effort and a drop of 18 bpm on the first minute of an active recovery.
- 3.
Normal increase of SBP: from 130/80 at rest to 210/100 at peak exercise.
- 4.
Hypertensive pattern on DBP: increase from 80 to 100 mmHg
- 5.
No arrhythmias, ST changes, and angina were found.
- 6.
The normalization during the exercise period of the T wave previously present in the rest ECG suggests the presence of stunned myocardium.
Comments
This is a typical case of a low-risk patient for CR, with normal LV ejection fraction, no residual ischemia, no arrhythmias, good exercise tolerance, and a normal adaptation of hemodynamic parameters to maximal exercise.
He was admitted to a formal CRP under medical supervision during some weeks, since he was wishing to start an exercise program and he didn’t had any previous physical activity habits.
Case #2
Male, 54 years old
CVD risk factors: Type 2 diabetes and hypertension.
Assessment performed before admission to CRP on the 4th of October 2004, following a noncomplicated CABG on the 11th of July 2004 and a previous inferior myocardial infarction in an indeterminate date.
He was submitted to complete revascularization, by a triple CABG with LIMA to LAD and single saphenous grafts to the second diagonal and posterior descendent arteries. Three months after surgery, a nuclear perfusion scan requested for routine clinical assessment and identified residual silent ischemia in the inferior wall (Fig. 1.2).
Fig. 1.2
Myocardial nuclear perfusion scan (case #2)
After this test, he was re-submitted to coronary angiography, and it was found that the graft to the posterior descendent artery was occluded and the artery was not amenable to PCI. He had good collateral circulation from the left coronary artery, and the other bypasses were patent, with normal flow. His attending cardiologist decided to keep him on medical therapy and send him to CR.
Before the CRP, he was submitted to an ET, under his usual medication: bisoprolol (5 mg, od), IMN (50 mg, od), losartan (50 mg, od), enalapril (20 mg, od), HCTZ (12.5 mg, od), simvastatin (20 mg, od), ASA (100 mg, od), and two oral antidiabetic drugs (Table 1.6).
Table 1.6
Admission exercise test (case #2)
Stage | Speed Km/h | Grade % | METs | HR bpm | SBP mmHg | DBP mmHg | Symptoms | ECG |
|---|---|---|---|---|---|---|---|---|
Rest | 0 | 0 | 1 | 59 | 130 | 80 | No | Q waves on DII, DIII, and aVF |
I | 2.7 | 10 | 4.6 | 113 | 150 | 80 | No | No change |
II | 4.0 | 12 | 7.0 | 131 | 170 | 80 | Intense fatigue | ST downslope of 1 mm in V5-V6 |
Exercise duration, 6 min 00 sec; onset of ischemia, at 4 min 00 s with 123 bpm | ||||||||
Rec. 1’
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