The total amplitude of the QRS compared with exercise usually decreases near peak workload, as well as the T-wave amplitude, and there is a tendency towards right axis deviation. The QRS duration does not change significantly. If the stroke volume increases the T-wave may initially increase, which occurs early in exercise with moderate workloads. A decrease in R-wave is more likely to be seen immediately after the exercise period, however, rather than during it. When considering the QRS in the various leads during maximum exercise, there is a tendency towards a reduction in R-wave or S-wave amplitude; this is more marked in normal than in abnormal subjects. The decreased amplitude following a peak exercise period may be due to decrease in systolic and possibly diastolic volumes that often develop after peak cardiac output is attained.This is termed the body effect, and found that left ventricular forces decreases stroke volume decrease and that right ventricular forces usually increase at the same time. In ischaemia, the systolic volume increases stroke volume decreases and the left ventricular R-waves any become taller.
R-Wave Amplitude
The R-wave amplitude in the lateral precordial leads usually decreases more in normal than in abnormal subjects and correlates with left ventricular function. Patients with CAD (severe) are likely to have an increase in the R-wave amplitude with exercise. As exercise progresses and the heart rate increases, R-wave amplitude increases normally until the heart rate is approximately 120 or 130 beats per minute, and then the amplitude begins to decrease. This suggests that for the R-wave to have significance, an increase in amplitude should be at a heart rate greater than 120 bpm. The sensitivity of an R-wave increase is rather poor but the specificity can be good if the patient reaches high heart rates. Stress test responses are difficult to analyze in patients with LBBB. Lee and colleagues reported that R-wave changes in 23 patients with LBBB had a 93 per cent sensitivity, 88 per cent specificity and 93 per cent predictability. A reduction in amplitude helps to predict normal coronary arteries and good left ventricular function in LBBB. Berman and associates used the sum of the R-waves in aVL, aVF and V3 and V4, plus S and V1 and V2 and were able to identify CAD in 93 per cent of 230 patients subsequently studied with coronary angiography. An R-wave increase is reported with vasospastic angina and early in the course of a myocardial infarction, where it is predictive of the severity and the likelihood of severe arrhythmias.
Increased QRS Duration
The duration of the QRS is usually reduced slightly during exercise. Because catecholamines increase conduction velocity in the Purkinje fibers and through the ventricular muscle. A number for studies show that ischaemia reduces the conduction velocity. The greatest prolongation is found in those with three vessel disease.
Athens Score
Changes in R-waves, S-waves and Q-waves have all shown some usefulness, but each is a weak predictor of CAD. Therefore, Michaelides and colleagues, have proposed an index or score to combine these factors. By combining the amplitude changes of the three waves in the formula
mm = (DR – DQ – DS) aVF + (DR – DQ- DS) V5 and using a cutoff of less than 5 mm, they were able to obtain a sensitivity of 75 per cent and a specificity of 73 per cent. This was better than using ST depression alone.
Changes QRS Axis
As exercise progresses in normal subjects the QRS axis rotates to the right but when patients have significant LAD narrowing, exercise results in a leftward rotation of the frontal axis. Patients with a single vessel right coronary artery disease rotate to the right and thus are indistinguishable from normals.
Changes S-Wave
The S-wave increases with ischaemia especially when patients also had ST-segment depression. It is found that the S-wave increases in normal individuals and in ischaemic patients occasionally in the absence of ST depression.
Septal Q-Waves
It has been noted that there is an increase in septal Q-waves in normals and a lack of this response in patients with significant ischaemic ST depression. The disappearance is probably due to the loss of contractility secondary to ischaemia. This decrease in septal Q-waves has been correlated on coronary angiography in the LAD disease. Although Q-wave in the anterior precordial leads are often missing, when they are present, they may aid in the differentiation between true positive and false positive. ECGs when ST depression is associated with an enlarging septal Q, it is rarely due to ischaemia, or at least not due to LAD narrowing.
R-Wave Amplitude
The R-wave amplitude in the lateral precordial leads usually decreases more in normal than in abnormal subjects and correlates with left ventricular function. Patients with CAD (severe) are likely to have an increase in the R-wave amplitude with exercise. As exercise progresses and the heart rate increases, R-wave amplitude increases normally until the heart rate is approximately 120 or 130 beats per minute, and then the amplitude begins to decrease. This suggests that for the R-wave to have significance, an increase in amplitude should be at a heart rate greater than 120 bpm. The sensitivity of an R-wave increase is rather poor but the specificity can be good if the patient reaches high heart rates. Stress test responses are difficult to analyze in patients with LBBB. Lee and colleagues reported that R-wave changes in 23 patients with LBBB had a 93 per cent sensitivity, 88 per cent specificity and 93 per cent predictability. A reduction in amplitude helps to predict normal coronary arteries and good left ventricular function in LBBB. Berman and associates used the sum of the R-waves in aVL, aVF and V3 and V4, plus S and V1 and V2 and were able to identify CAD in 93 per cent of 230 patients subsequently studied with coronary angiography. An R-wave increase is reported with vasospastic angina and early in the course of a myocardial infarction, where it is predictive of the severity and the likelihood of severe arrhythmias.
Increased QRS Duration
The duration of the QRS is usually reduced slightly during exercise. Because catecholamines increase conduction velocity in the Purkinje fibers and through the ventricular muscle. A number for studies show that ischaemia reduces the conduction velocity. The greatest prolongation is found in those with three vessel disease.
Athens Score
Changes in R-waves, S-waves and Q-waves have all shown some usefulness, but each is a weak predictor of CAD. Therefore, Michaelides and colleagues, have proposed an index or score to combine these factors. By combining the amplitude changes of the three waves in the formula
mm = (DR – DQ – DS) aVF + (DR – DQ- DS) V5 and using a cutoff of less than 5 mm, they were able to obtain a sensitivity of 75 per cent and a specificity of 73 per cent. This was better than using ST depression alone.
Changes QRS Axis
As exercise progresses in normal subjects the QRS axis rotates to the right but when patients have significant LAD narrowing, exercise results in a leftward rotation of the frontal axis. Patients with a single vessel right coronary artery disease rotate to the right and thus are indistinguishable from normals.
Changes S-Wave
The S-wave increases with ischaemia especially when patients also had ST-segment depression. It is found that the S-wave increases in normal individuals and in ischaemic patients occasionally in the absence of ST depression.
Septal Q-Waves
It has been noted that there is an increase in septal Q-waves in normals and a lack of this response in patients with significant ischaemic ST depression. The disappearance is probably due to the loss of contractility secondary to ischaemia. This decrease in septal Q-waves has been correlated on coronary angiography in the LAD disease. Although Q-wave in the anterior precordial leads are often missing, when they are present, they may aid in the differentiation between true positive and false positive. ECGs when ST depression is associated with an enlarging septal Q, it is rarely due to ischaemia, or at least not due to LAD narrowing.
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