Interpretation of the Electrocardiogram

Abstract

MANUAL OF EXERCISE TESTING1975-Simoons and Hugenholtz 5 reported Frank lead vectorcardiographic changes during exercise in normal subjects. The direction and magnitudes of time-normalized P, QRS, and ST vectors and other QRS parameters were analyzed during and after exercise in 56 apparently healthy men, ages 23 to 62 years. The PR interval and the P-wave amplitude increased during exercise. Direction of the P vectors did not change, differing with previous reports that had noted changes consistent with right atrial overload. No significant change in QRS magnitude was observed, and the magnitude in spatial orientation and the maximum QRS vectors remained constant. QRS onset to T-wave peak shortened. The terminal QRS vectors and the initial ST vectors gradually shortened and shifted to the right and upward. The T-wave amplitude lessened during exercise. In the first minute of recovery, the P and T magnitudes markedly increased, and then all measurements gradually returned to the resting level. There was an increase in S-wave duration in leads X and Y, and right-axis shift in the QRS complex was heart rate dependent. The ST-segment shifted upward to the right and posterior, and T-wave magnitude increased markedly in the first minute of recovery. The QRS complex shortened in some young individuals during exercise. 1979-The United States Air Force Medical Corps (USAFMC) NormalAircrewmen Study was based on digital data from 40 low-risk normal subjects, processed, and analyzed across treadmill times on the basis of waveform component and lead. 6 USAFMC Normal Aircrewmen StudyFigure 4-1 illustrates the waveforms produced using median values of the measurements of all 40 subjects for leads V5, aVF (Y), and V2 (Z). These figures demonstrate the specific waveform alterations that occur in response to maximal treadmill exercise. Supine, exercise to a heart rate of 120 beats per minute, maximal exercise, 1-minute recovery, and 5-minute recovery were chosen as representative times. There is depression of the J junction and peaking of the T waves at maximal exercise and at 1-minute recovery. Along with the J-junction depression (QRS end or ST0), marked ST upsloping is seen. J-junction depression did not occur in the Z lead (which is equivalent to and of the same polarity as V2). As the R wave decreases in amplitude, the S wave increases in depth. The QS duration shortens minimally, but the RT duration decreases in a larger amount. Q-Wave, R-Wave, and S-Wave AmplitudesIn leads CM5, V5, CC5, and Y, the Q wave shows very small changes from the resting values; however, it does become slightly more negative at maximal exercise. Q-wave changes were not noted in the Z lead. Changes in Key Point: Junctional ST depression below the PR isoelectric line is normally seen with increasing heart rate, and early repolarization normally decreases to or below the isoelectric line.median R-wave amplitude are not detected until near-maximal and maximal effort is approached. At maximal exercise and on into 1-minute recovery, a sharp decrease in R-...

The Clinical Utility of Cardiopulmonary Exercise Testing in Suspected or Confirmed Myocardial Ischemia

“…Similar reductions in diagnostic accuracy are found when the effects of digoxin, LV hypertrophy, and resting ST depression are removed from the analysis. 83 Many other studies have confirmed these findings and echo these limitations. Combined with estimates of exercise capacity, the standard exercise ECG has been shown to be prognostic of future cardiac events.…”