The QRS score: a promising new exercise score for detecting coronary artery disease based on exercise-induced changes of Q-, R- and S-waves: a relationship with myocardial ischaemia.

BACKGROUND

Recently, a new exercise test criterion diagnosing coronary artery disease was proposed, based on a composite of changes in Q-, R- and S-waves: the QRS score. We compared this new criterion with conventional ST-segment depression and other compositions of Q-, R- and S-wave changes in patients and normals and related the QRS score to reversible thallium-201 scintigraphic defects and ST-segment depression as markers for ischaemia. The influence of beta-blockade on the QRS score was also studied.

METHODS

The study population consisted of 155 persons with 53 normals (group I) and 102 patients with documented coronary artery disease (group II). Another 20 patients (group III) with proven coronary artery disease and a positive exercise test by ST-segment criteria were studied for the influence of beta-blockade on the QRS score. A symptom-limited exercise protocol according to the modified Bruce protocol was used. For the QRS score, Q-, R- and S-wave amplitudes which could be recovered immediately were subtracted from pretest values: delta Q, delta R, delta S respectively. The score was calculated by the formula: (delta R - delta Q - delta S)AVF + (delta R - delta Q - delta S)V5.

RESULTS

Using a cut-off point of > 5 as normal, the QRS score resulted in a sensitivity of 88.2%, a specificity of 84.8% and a predictive accuracy of 87.1%. For ST-segment depression these values were 54.9%, 83% and 64.5% respectively (P < 0.001 compared to the QRS score). Predictive accuracies of changes in Q-, R- and S-waves in leads AVF and V5 separately, combinations of changes and combining the two leads, resulted-with the exception of solitary S-wave changes-in predictive accuracies higher than those of ST-segment depression, but all were lower than the QRS score. We found a significant correlation between the QRS score, the summed ST-segment depression (P < 0.004) and the extent of reversible thallium-201 defects (P < 0.001). Applying Bayes' theorem, the combination of an abnormal QRS score and ST-segment depression resulted in the highest post-test risk for coronary artery disease and a normal QRS score without ST-segment depression in the lowest post-test risk. The QRS score and the maximal ST-segment depression changed significantly under the influence of beta-blockade (P < 0.02 and P < 0.001 respectively).

CONCLUSION

Our data suggest that an abnormal QRS score reflects myocardial ischaemia. Furthermore, for the interpretation of the exercise test, the combined analysis of ST-segments and the QRS score is of value for the prediction of the presence or absence of coronary artery disease and its follow-up.