• Fitness & Health
• Sport & Exercise Science
• Physical Education
• Strength & Conditioning
• Sports Medicine
• Sport Management
• Dance

Electrocardiogram ECG abnormalities during rest, exercise, and recovery

This is an excerpt from Clinical Exercise Physiology 6th Edition by Jonathan K Ehrman,Paul Gordon,Paul S. Visich,Steven J. Keteyian.

By Alexander H.K. Montoye, PhD, and Marlene R. Wenta, MA

Our analysis of the 12-lead ECG, which is based on recognizing normal and abnormal findings at rest, during exercise, and in recovery, is intended as a review of issues specifically evaluated and encountered before, during, and immediately following GXTs. When assessing the resting ECG before the GXT, the health care professional should consider their interpretation against the patient’s medical history to determine whether any discrepancies are present. For example, the patient stated no previous myocardial infarction, but the current ECG shows significant Q waves (typically a sign of previous infarction) throughout the anterior leads. Also important is a comparison of the patient’s current resting 12-lead ECG against a previous ECG (ideally from when the patient was known to be healthy), especially when an abnormality is detected. (For example, the patient’s current resting ECG rhythm shows atrial fibrillation; is this arrhythmia new or old?) When a clinically significant difference is detected on the resting ECG and it appears to be a new finding, the supervising or referring physician should be informed before the GXT is undertaken. This is especially true if the new finding influences the ability to assess the ST segment, which will be discussed in more depth later in the chapter.

The most common reason to complete a diagnostic GXT with a 12-lead ECG is to assess for potential myocardial ischemia due to coronary heart disease (CHD). However, in certain patients, abnormalities in their ECG at rest preclude use of the ECG during exercise to accurately detect or determine exercise-induced myocardial ischemia. Therefore, in these patients, an exercise- or pharmacology-induced stress test is typically completed in conjunction with cardiac imaging by echocardiography or radionuclide testing. The following are common abnormalities in the resting ECG that limit the sensitivity of the exercise ECG to detect ischemia because they present ECG changes typically associated with ischemia or myocardial infarction, thereby increasing the risk of a false-positive test (i.e., ST deviation occurs, but it is not truly related to ischemia or infarction):

• Left bundle branch block
• Right bundle branch block (ST changes in anterior leads V1-V3 cannot be interpreted, but remaining leads are interpretable)
• Preexcitation syndrome (Wolff-Parkinson-White)
• Nonspecific ST-segment or T-wave changes with [greater than] 1 mm depression
• Abnormalities due to digoxin therapy
• Left ventricular hypertrophy
• Electrolyte abnormalities such as hypokalemia
• Electronically paced ventricular rhythm

Conversely, although it would not show on an ECG, certain instances, such as patient use of β-blocker medication, have the opposite effect. A patient might fail to reach an ischemic threshold, either because of impaired exercise tolerance or a blunting of heart rate or blood pressure that lowers rate pressure product (discussed later in chapter) below the ischemic threshold, thereby masking what might otherwise present as ST depression and increasing the chances of a false-negative test (i.e., no ST deviation occurs, but the person has CHD that would otherwise result in ischemia). If a GXT is being done for diagnostic purposes, the ordering medical provider should determine whether a patient should be on or off medications that could inhibit the ability to detect ischemia.

During the GXT, one health care professional should continuously observe the real-time ECG tracing to identify the onset and nature of any ECG change. The evaluation of the ST segment is of great importance because of its ability to suggest the onset of ischemia. In addition, the onset of arrhythmias should be noted, especially those related to indications for test termination (see the sidebar ECG GXT Contraindications and Indications to Terminate a GXT). Although the onset and progression of ST depression are subtle in most cases, arrhythmias can occur suddenly and can be brief, intermittent, or sustained.

Before, during, and immediately after a GXT, all 12 ECG leads should be monitored; however, V5 is the one most likely to demonstrate ST-segment depression, whereas the inferior leads (II, III, and aVF) are associated with a relatively higher incidence of false-positive findings. V5 is the most diagnostic lead because when true ischemia occurs with exertion, it is most likely to be observed in this lead. When the test supervisor recognizes ST-segment changes, they should note the exercise time and the work rate (i.e., METs) at onset, the heart rate and blood pressure measured most closely in time to ST changes (in order to calculate the rate pressure product at the ischemic threshold), the morphology (shape of the ST segment; see next paragraph), and the magnitude (e.g., 2 mm), as well as document any corresponding symptoms (e.g., chest pain, shortness of breath, dizziness).

ST-Segment Depression

Of the potential ST-segment changes, ST-segment depression is the most frequent response during exercise and is suggestive of subendocardial ischemia. Horizontal or downsloping ST-segment depression of ≥1 mm that occurs 0.08 s (i.e., 80 ms) past the J point is recognized as a positive test for myocardial ischemia (figure 5.7). When ST-segment changes of this type occur along with typical angina symptoms, the likelihood of CHD is high. In addition, the earlier the onset, the greater the ST depression, the more leads with ST depression, and the more time it takes for the ST depression to resolve in recovery, the more likely it is that clinically significant CHD is present. In some cases, ST-segment depression is observed only in recovery, yet it should be treated as an abnormal response. Additionally, J-point depression with an upsloping ST segment that is more than 1.5 mm depressed at 0.08 s past the J point is also suggestive of exercise-induced ischemia.

ST-Segment Elevation

ST-segment or J-point elevation observed on a resting ECG is often attributable to early repolarization and is not necessarily abnormal in healthy people, but this should be noted if present to avoid potential false-positive findings on a GXT. With exertion, this type of ST elevation normally returns to the isoelectric line. New ST-segment elevation with exertion (assuming the resting ECG is normal) is a somewhat rare finding and may suggest transmural ischemia or a coronary artery spasm. This type of ST-segment elevation is an absolute reason for stopping the test (see the sidebar ECG GXT Contraindications and Indications to Terminate a GXT). When Q waves are present on the resting ECG from a previous infarction, ST elevation with exertion may reflect a left ventricular wall motion abnormality. Additionally, ST elevation that persists following a myocardial infarction may indicate ventricular aneurysm. If the ST elevation is a new finding, this may require further testing (e.g., echocardiography) to detect the degree of wall motion abnormality. It would be important for the CEP to contact the referring medical provider prior to completing the GXT. ST-segment elevation can localize the ischemic area and the arteries involved, whereas this is not always the case with ST-segment depression.^{8, 19}

T-Wave Changes

In healthy individuals, T-wave amplitude initially decreases gradually with the onset of exercise. Later, at maximal exercise, T-wave amplitude increases. T-wave inversion with exertion is sometimes associated with ischemia, but this is a nonspecific finding because T-wave inversion can also be caused by numerous other conditions, such as ventricular hypertrophy or left or right bundle branch block.⁹

It remains undecided whether inverted T waves present on the ECG at rest that then normalize with exertion reflect myocardial ischemia. Normalization of T waves is also present during ischemic responses associated with coronary spasms; however, this finding has the greatest significance under resting conditions. Overall, T-wave changes with exertion are not specific to exercise-induced ischemia but should be correlated with ST-segment changes and other signs and symptoms.

Arrhythmia

Aside from evaluating ST or T-wave changes with exertion, arrhythmias are of equal clinical importance and potentially more life-threatening, based on the suddenness in which arrhythmias may appear. Although a GXT is most commonly used to diagnose potential CHD, this test can also evaluate symptoms (e.g., near syncope) attributable to an arrhythmia. In addition, a GXT may be used to evaluate the effectiveness of medical therapy in controlling an arrhythmia or evaluating a patient’s blood pressure with exertion. The supervisor of a GXT must have a strong knowledge of arrhythmia detection and be able to respond appropriately and quickly, because some necessitate immediate cessation of exercise and may require emergency response, especially if symptomatic (e.g., causing syncope). When arrhythmias appear during a GXT, the onset of the arrhythmia and any associated signs or symptoms should be documented, along with any other ECG changes (e.g., ST depression). (Note: Documenting no symptoms is just as important as documenting symptoms at each stage of a GXT.) The health care professional supervising the GXT should be knowledgeable about and able to recognize three major types of ECG rhythm or conduction abnormalities during exercise:

1. Supraventricular arrhythmias that compromise cardiac function (e.g., paroxysmal SVT, atrial flutter, atrial fibrillation)
2. Ventricular arrhythmias that have the potential to progress to a life-threatening arrhythmia (e.g., ventricular tachycardia and fibrillation)
3. The onset of high-grade conduction abnormalities (e.g., second-degree type 2 and third-degree AV block)

More Excerpts From Clinical Exercise Physiology 6th Edition

---