Importance of Reciprocal ST Segment Depression in the Extensive Coronary Artery Disease

Aim: We investigated the relationship between the severity of reciprocal ST depression and the extent of coronary artery disease in patients with inferior myocardial infarction. Method: Ninety-five consecutive patients (52 women 43 men, with a mean age of 54±5 years) who had acute inferior myocardial infarction were included in the study. Reciprocal changes in the ST segment were defined as ST depression of >1 mm in at least two out of four of the precordial leads V1–V4. All the patients had undergone coronary angiography within seven days of admission. The extension of coronary artery disease which was measured by Gensini and Reardon scores, was compared with the reciprocal changes on ECG recorded at the time of admission. Result: There was a significant correlation between reciprocal ST depression and disease extension (r=0.68 for Gensini score, r= 0.88 for Reardon score, p<0.05 for both). Conclusion: The presence of ST segment depression in the precordial leads during the acute inferior myocardial infarction was associated with greater myocardial necrosis and more frequent left coronary artery disease.


INTRODUCTION
Over the past 2 decades, the 12-lead electrocardiogram (ECG) has attained special significance for the diagnosis and triage of patients with chest pain because timely detection of myocardial injury and a rapid assessment of myocardium at risk proved pivotal to implementing effective reperfusion therapies during acute myocardial infarction (1).Henry Marriott wrote that the electrocardiogram is "the single most often used, most cost-effective, and most diagnostic test in cardiology" and also "the most frequently misinterpreted" (2).The ECG changes were and still are considered as a primary reflection of the injured myocardial zone.Reciprocal ST segment depression (RSTD) is a well known ECG sign often accompanying ST segment elevation myocardial infarction (STEMI).The ST depression is captured by a lead placed at 180 degrees of the lead recording the ST elevation, although the terms "reciprocal" and "mirror" are loosely applied to recording points in the complementary electrocardiographic spatial plane as well (11).Its significance and prognostic value have been the subject of many reports.Anterior RSTD accompanying acute inferior myocardial infarction was shown to be attributable to the co-existent left anterior descending artery (LAD) disease (4,5), lower left ventricular ejection fraction (LVEF) (6,7) and poor prognosis.
However conflicting results were also reported (8,9).This study was conducted to investigate the relationship between the severity of RSTD and the extent of coronary artery disease.

MATERIAL AND METHODS
Ninety-five consecutive patients (52 women 43 men, with a mean age of 54±5 years) who had acute inferior myocardial infarction with RSTD were included in the study.Acute inferior wall MI was diagnosed by: typical chest pain at least 30 minutes, ST-segment elevation of more than 0.1 mV in at least two leads representing the inferior wall (DII, DIII, AVF), and an increase in cardiac enzymes to more than twice of normal (5 IU/L for creatine kinase MB isoenzyme).The presence of right ventricular infarction was defined by an ST segment elevation ≥0.1 mV in lead V4R.R wave to S wave ratio>1 in V1and V2 was defined as posterior MI.Reciprocal changes in the ST segment were defined as ST depression of >1 mm in at least two out of four of the precordial leads V1-V4.
Exclusion criteria were previous MI, previous revascularization, associated posterior or right ventricular MI, intraventricular conduction disturbances, valvular heart disease, hypertrophic, dilated, or restrictive cardiomyopathies, and significant arrhythmias including atrial fibrillation, supra ventricular or ventricular tachycardia, and ventricular bigeminy.A standard 12-lead ECG was recorded immediately after arrival at the coronary care unit.Reciprocal changes in the ST segment were defined as ST depression of >1 mm in at least two out of four of the precordial leads V1-V4 in patients with inferior infarction.All the patients had undergone coronary angiography within seven days of admission.Coronary angiography was performed by the femoral approach with 6 French diagnostic catheters.Images were recorded in multiple projections for left and right coronary arteries on a digital system.Two cardiologists who were blinded for the characteristics of the patients during the interpretation made the interpretation of the coronary angiograms.
The extension of coronary artery disease was measured by Gensini (12) and Reardon (13) scores.Gensini score which grades narrowing of the lumens of the coronary arteries as 1 point for 1-25% narrowing, 2 for 26-50% narrowing, 4 for 51-75% narrowing, 8 for 76-90% narrowing, 16 for 91-99% narrowing, and 32 for total occlusion (12).This score is then multiplied by a factor that takes into account the importance of the lesion's position in the coronary arterial tree, for example, 5 for the left main coronary artery, 2.5 for the proximal left anterior descending coronary artery and proximal left circumflex coronary artery (3.5 if left circumflex coronary artery is dominant), 1.5 for the mid-region of the left anterior descending coronary artery, 1 for the distal left anterior descending coronary artery, the first diagonal, the proximal, mid and distal-region of the right coronary artery, the postero-descending, the mid-and distal-region of the left circumflex coronary artery (2 for both of them if left circumflex coronary artery is dominant) and the obtuse margin, and 0.5 for the second diagonal and the postero-lateral branch.The Gensini score was expressed as the sum of the scores for the all coronary arteries.In Reardon score system we divided coronary arteries to four parts (Left main, Left anterior descending, right coronary, circumflex artery).Each part divided to segments.Atherosclerotic lesion of each segments was scored (Normal: 0 point, <50%:1 point, 50-74%:2 point, 75-99%:3 point, 100%:4 point).Total scores were calculated by sum of each segments score (13).ECG measurements were performed as previously described by a single reader who was blinded to the angiographic findings and clinical findings, by use of electronic calipers (14).The amount of ST segment depression at 0.08 second after the J point in the reciprocal leads on admission 12-lead electrocardiograms of the patients were also evaluated for the quantification of RSTD (mm).The correlation between the RSTD and angiography scores was investigated.Informed consents were obtained from patients and local ethic committee approved the study protocol.

Statistical Analysis
Parametric variables presented as a mean± standard deviation, nonparametric variables presented as a frequency and percent.Spearman's rho test was used for correlation analysis.p <0.05 was considered significant.

RESULTS
The clinical and demographic features of the patient population are presented in Table 1.Ninety-five patients who underwent detailed electrocardiographic coding were included in the analysis comprising 43 (45.26%)men and 52 (54.74%) women.
Mean age of the cohort was 54.3±5 years.17 patients (18%) had hypertension, 24 (25%) had diabetes mellitus and 27 patients (28%) was smoker.The mean values of RSTD , Gensini and Reardon scores were found to be 3.73±2.75mm, 31.2±30.2and 7.25±3.54,respectively.There was also a significant positive linear correlation between the RSTD and angiography scores (r=0.68 for Gensini, r= 0.88 for Reardon, p<0.05 for both).Men and women did not differ significantly with regard to these parameters and correlations.

DISCUSSION
The significance of reciprocal ST segment depression on the electrocardiogram during the early stages of myocardial infarction has interested many researchers and has been the subject of many debates regarding its mechanism.Opinion is divided as to whether it is a sign of multivessel coronary disease and an adverse prognosis (5), or a benign electrical phenomenon (4)(5)(6).The significance of anterior ST depression accompanying inferior transmural injury, on the other hand, may depend on the leads involved.ST depression in leads V1 through V3 or DI to AVL appears to correspond to mere mirroring, often from circumflex artery occlusion (15).Lee (20).Our data demonstrated a significant positive linear correlation between the RSTD and angiography scores (Gensini-Reardon) indicating severe RSTD as a marker of extensive coronary artery disease.
Limitations of the study: The study lacks a control group.
Comparison with a control group without reciprocal depressions would yield more accurate results.
In conclusion, the presence of ST segment depression in the precordial leads during the acute phase of inferior myocardial infarction was associated with greater myocardial necrosis and more frequent left coronary artery disease, thus identifying a subset of high risk patients.

Table 1 :
Patient Characteristics of the study group