Question

List and describe the normal ECG changes that occur during the submaximal and maximal stages of a graded exercise test (GXT) (i.e. changes in wave amplitudes, interval durations, etc). Describe why the physiological reason(s) that these changes occur (for example: R-R interval decreases dramatically during exercise. This occurs because heart rate increases during exercise in order to increase cardiac output/blood flow to the working muscles).

Answer 1

The changes that occur during the submaximal and maximal stages of GXT are :-

- ST depression

an abnormal ecg response is >1.0 mm of horizontal or downslopping ST 60-80beyond the J point, suggesting ischemia.

-ST segment depression (depression of the J point and the slope at 80 msec past the J point) is the most common manifestation of exercise induced myocardial ischemia.

-Horizontal or downsloping ST segment depression is more indicative of myocardial ischemia then is upsloping depression.

-ST segment depression does not localize ischemia to a specific area of myocardium

-the more leads with apparent ischemic ST-segment shifts the more severe the disease

-Significant ST-segment depression occurring only in recovery likely represents a TRUE positive response and should be considered an important diagnostic finding.

- ST segment elevation

St elevation displays a previous Q-wave MI almost always reflects and aneurysm or wall motion abnormality. Acute MI, NO oxygen

- may be seeing in the normal resting ECG. increasing HR usually causes these elevated ST segments to return to isoelectric line.

- EXERCISE INDUCED st-segment elevation in leads with Q waves consistent with a prior myocardial infarction may be indicative of wall motion abnormalities, ischemia or both.

- Supraventricular Dysrythmias

isolated atrial ectopic beats or short runs of SVT commonly occur during exercise testing and do not appear to have any diagnostic or prognostic significance for CVD

- Ventricular Dysrythmias

VTACH w/CAD, Good indicator that things are not ok. PVC's that increase in frequency, complexity, or both do not necessarily signify underlying problems. Complex ventricular ectopy including paired or multiform PVC's and runs of v tach >3 are a good indicator of CAD

This changes occurs because heart rate increases during exercise in order to increase cardiac output/blood flow to the working muscles).