Author + information
- Received June 27, 1996
- Revision received October 31, 1996
- Accepted November 12, 1996
- Published online March 1, 1997.
- Tuvia Ben-Gal, MDA,
- Samuel Sclarovsky, MDA,*,
- Itzhak Herz, MDA,
- Boris Strasberg, MDA,
- Bruria Zlotikamien, MDA,
- Jaqueline Sulkes, PhDA,
- Yochai Birnbaum, MDA,
- Galen S Wagner, MD, FACCB and
- Alex Sagie, MDA
- ↵*Dr. Samuel Sclarovsky, Cardiology Department, Rabin Medical Center, Campus Beilinson, Petah Tikva 49100, Israel.
Objectives. This study assessed prospectively the correlation between the conal branch of the right coronary artery and the pattern of ST segment elevation in leads V1and V3R during anterior wall acute myocardial infarction (AMI).
Background. The traditional electrocardiographic (ECG) definition of anteroseptal AMI—ST segment elevation in leads V1to V3—has recently been challenged. The significance of ST segment elevation in lead V1during anterior wall AMI is unclear.
Methods. The admission 12-lead ECG with additional lead V3R and the coronary angiograms performed within 10 days of hospital admission were evaluated in 28 consecutive patients (mean age ± SD 62 ± 9 years) admitted to the coronary care unit with anterior wall AMI. Patients were classified into two groups according to the magnitude of ST segment elevation in lead V1: group A (elevation ≥1.5 mm, n = 12) and group B (elevation <1.5 mm, n = 16). Two types of conal branch were identified: small (not reaching the interventricular septum [IVS]) and large (reaching the IVS).
Results. ST segment elevation in lead V3R was found in 11 (92%) and 6 (37%) patients from group A and group B, respectively (p < 0.001); a small conal branch was seen in 10 (83%) and 3 (19%) patients, respectively (p < 0.001). Ten patients (all from group B) had a large conal branch.
Conclusions. ST segment elevation in lead V1in the admission ECG of patients with anterior wall AMI is strongly related to ST segment elevation in lead V3R and is associated with a small conal branch. Our findings suggest that lead V1reflects the right paraseptal area supplied by the septal branches of the left anterior descending coronary artery (LAD), alone or together with the conal branch. The absence of ST segment elevation in lead V1during anterior AMI suggests that the IVS is protected by a large conal branch in addition to the septal branches of the LAD (double circulation).
(J Am Coll Cardiol 1997;29:506–11)
The ability to predict noninvasively the occlusion site of the infarct-related coronary artery as well as the size and location of its vascular bed shortly after hospital admission may help the clinician to estimate the extent of the myocardial area at risk and plan the appropriate therapeutic intervention. This ability can be crucial during anterior wall acute myocardial infarction (AMI) as documented by the detrimental outcome of proximal left anterior descending coronary artery (LAD) occlusion ([1–3]). The electrocardiogram (ECG) is a reliable tool for detecting anterior wall AMI [4–9] or infarction caused by obstruction of the LAD ([10, 11]). During the acute phase of anterior AMI, the ECG may show ST segment elevation in leads facing the anterior wall, lateral wall () and inferior wall () and also in leads facing the right ventricle ([14, 15]). On the basis of the ECG, several subtypes of anterior AMI have been recognized (anteroseptal, anterolateral, apical and extensive anterior) (); however, poor correlation has been reported between the various ECG subtypes and the exact anatomic location of the infarct as determined by autopsy ([7, 8, 12]) or echocardiography (). In particular, the frequent absence of involvement of the interventricular septum (IVS) in the traditional ECG “anteroseptal wall AMI” () suggests that the anatomic significance of ST segment elevation in lead V1during anterior AMI is questionable. Furthermore, investigators () have found no statistical significant correlation between the presence of ST segment elevation in leads V1to V3in the admission ECG and the presence of a proximal LAD lesion.
Right precordial lead V3(V3R), the lead anatomically closest to lead V1, represents the free wall of the right ventricle (). During inferior AMI, ST segment elevation >0.5 mm in lead V3R correlates highly with right ventricular infarction ([20, 21]). ST segment elevation in lead V3R has also been reported ([14, 15]) in ∼30% to 40% of patients with anterior AMI; however, whether this sign represents right ventricular free wall involvement or involvement of the right side of the IVS is unclear.
The blood supply to the anterior IVS may be derived from the septal branches of the LAD alone or together with the conal branch of the right coronary artery (RCA) (). We propose that ST segment elevation in leads V1and V3R during anterior AMI may signify ischemic involvement of the right side of the anterior IVS. Therefore, in this study we examined the relation between 1) ST segment elevation in leads V1and V3R during evolving anterior wall AMI, and 2) the coronary blood supply of the anterior IVS.
1.1 Study patients.
Between July 1993 and July 1994, 98 consecutive patients with anterior wall AMI were admitted to the coronary care unit at our institution. Twenty-eight patients (6 women and 22 men, mean age ± SD 62.4 ± 9.6 years [range 39 to 76]) fulfilled the following inclusion criteria and were enrolled in our study: 1) first myocardial infarction, 2) admission ECG with the standard 12 leads plus lead V3R, and 3) coronary angiography performed within 10 days of hospital admission. Patients were excluded from the study if they had: 1) ECG evidence or a history of previous myocardial infarction, 2) acute or chronic bundle branch block, or 3) ECG or echocardiographic evidence of left ventricular hypertrophy.
Anterior AMI was defined by chest pain lasting >30 min, evolving characteristic ECG abnormalities including ST segment elevation ≥2 mm in at least two consecutive precordial leads (V1to V4) and the typical increase in cardiac enzymes.
1.3 ECG evaluation.
A complete 13-lead ECG (including lead V3R) was recorded at admission using a paper speed of 25 mm/s and a standardization of 1 mV/10 mm. All ST segment deviations from the isoelectric line were measured manually to the nearest 0.5 mm 80 ms after the J point in every lead. All ECGs were evaluated separately by two investigators (T.B-G. and S.S.) without knowledge of the angiographic findings. The study patients were classified into two groups on the basis of magnitude of ST segment deviation in lead V1. Group A consisted of 12 patients with ST segment elevation ≥1.5 mm in lead V1and group B of 16 patients with ST segment elevation <1.5 mm in lead V1(Fig. 1). The cutoff value for ST segment elevation in lead V1(>1.5 mm) was chosen to distinguish predominant right paraseptal involvement, as represented by that lead, from the effect of the infarction in the adjacent left septal wall, as represented by ST segment elevation in lead V2(commonly >2.0 mm).
1.4 Coronary angiographic evaluation.
Patients were referred for coronary catheterization if they had evidence of postinfarction ischemia or ECG findings of a non-Q wave myocardial infarction. Selective coronary cineangiography was performed with the Judkins technique within 10 days (mean 5 ± 4) of admission. Cine recordings of the left coronary system were made in at least four projections (right anterior oblique [RAO], left anterior oblique [LAO], anteroposterior cranial and caudal) and of the right coronary system in at least two projections (RAO and LAO). When more than one lesion was present in the LAD, the site of the culprit lesion was determined by the angiographic appearance of either residual thrombus or ulcerated plaque. The location of the culprit lesion in the LAD was determined to be proximal or distal to the origin of the first major septal branch. Analysis of the right coronary system included the type of the conal branch according to the following definitions: small conal branch (diameter <0.5 mm) not reaching the IVS (Fig. 2) and large conal branch (diameter >0.5 mm) reaching the IVS (Fig. 2). The films were interpreted by two experienced angiographers without knowledge of the ECG findings. In case of a discrepancy, a third investigator read the film. The degree of stenosis was defined as the greatest reduction in percent lumen diameter in any view compared with the diameter of the nearest normal segment.
1.5 Statistical analysis.
All analyses used Statistical Analysis System (SAS) software. A probability value < 0.05 was considered statistically significant. To compare means of continuous variables (age) between group A and group B, a Student ttest was performed. The distribution of patients in groups A and B in regard to ST segment elevation in leads V3R and V2, the presence of a large conal branch and lesion site in the LAD (proximal or distal to the branching of the first septal artery) was analyzed by using the chi-square test or Fisher exact test if appropriate. A logistic regression model was fitted to the data to predict the presence of a small conal artery by ST segment elevation in lead V1. Odds ratios were calculated from the model.
2.1 Clinical characteristics.
There was no difference in mean age, male/female ratio, history of hypertension, smoking habits, diabetes mellitus, hyperlipidemia or use of thrombolytic therapy between the two groups (Table 1).
2.2 ECG analysis.
Eleven patients (92%) in group A had concomitant ST segment elevation in lead V3R versus only 6 (37%) of the 16 patients in group B (p < 0.001) (Table 2). Twenty-three patients had ST segment elevation in lead V2; of these, 11 patients (48%) had concomitant ST elevation in lead V1(p = 0.35) (Table 2).
2.3 Coronary angiographic analysis.
A conal branch was identified in 23 of the 28 patients enrolled in the study; of the other 5 patients, 2 were in group A and 3 in group B. Thirteen patients had a small conal branch (10 and 3 in group A and group B, respectively), and 10 patients (all from group B) had a large conal branch (Table 3, Fig. 2, A and B). No significant relation was found between the site of the LAD lesion in relation to the origin of the first septal branch and ST segment elevation in lead V1; it was proximal to the first septal branch in 9 patients (75%) in group A and in 9 patients (56%) in group B. There was no difference in the frequency of one-, two- or three-vessel disease or right dominance between the two groups.
The logistic regression model identified a 27-fold increase in the presence of a small conal branch with an increase of 1.0 mm in the ST segment elevation in lead V1(odds ratio 8.27, confidence interval 1.23 to 55.54).
We found that ST segment elevation in lead V1in the admission ECG of patients with anterior AMI is strongly related to ST segment elevation in lead V3R and is also associated with the presence of a small conal branch not reaching the IVS. No association was found between ST segment elevation in lead V1and lead V2in patients with anterior AMI or with the site of the LAD lesion in relation to the first septal origin.
3.1 Significance of ST segment changes in lead V1during anteroseptal AMI.
Ischemic ECG changes in precordial leads V1to V3have long been related to involvement of the IVS ([4, 12, 23]). Although the ECG is quite reliable in detecting anterior AMI ([4–9]), the relation between the traditional ECG “anteroseptal wall AMI” (ST segment elevation >2 mm in leads V1to V3) and the anatomic site of the infarction as examined at autopsy () or in echocardiographic studies () has not been thoroughly investigated. In some cases of anterior AMI, ischemic changes were seen in leads V2to V3, sparing involvement of lead V1; in others, the ischemic changes included lead V1. It has been previously shown () that ischemic changes in lead V1during anterior AMI are related to proximal LAD obstruction. However, recently, no significant difference in ST segment deviation in lead V1was found () between patients with an LAD lesion proximal to or distal to the first septal branch. In the present study, in accordance with the latter report, we found no relation between ST segment elevation in lead V1and the site of the LAD lesion during anterior AMI.
3.2 Significance of ST segment changes in lead V3R during anterior AMI.
Ischemic changes in lead V3R, commonly representing right ventricular involvement complicating inferior wall AMI, are also reported in 30% to 40% of patients during anterior wall AMI ([14, 15]). The clinical significance of ST segment elevation in lead V3R in patients with anterior AMI is yet unclear, and this finding is not included in the ECG subtypes of anterior AMI described by Schamroth (). ST segment elevation in lead V3R in anterior AMI has previously been reported () to correlate with the extent of the infarct () and with an LAD lesion proximal to the origin of the first septal branch. Cabin et al. (), in autopsy studies, found right ventricular free wall involvement in 13% of patients who died of anterior AMI, whereas Isner and Roberts () in a similar study found no such right ventricular involvement. It may be that ST segment elevation in lead V3R during anterior AMI represents ischemic damage to the right paraseptal region; however, none of these studies examined that region.
3.3 Relation between ST segment elevation in leads V1and V3R during anterior AMI (“solid angle” theory).
Because the precordial leads are close to the heart (specific leads closer to specific areas), the solid angle constructed depends on the proximity and dimensions of the area the electrode overlies (). Recently, we () observed a subtype of anterior AMI consisting of ST segment elevation in nonconsecutive leads: only in leads V2and aVL, pointing out the distinct anatomic region reflected by lead V2from that of leads V1and V3. Our findings, supported by the “solid angle” theory, reflect the poor anatomic relation of lead V1to lead V2and the close anatomic relation of lead V1to lead V3R. Because almost all patients with ST segment elevation in lead V1were found to have concomitant ST elevation in lead V3R, it can be assumed that ST segment elevation in these two leads represents the same anatomic region.
3.4 Interventricular septal blood supply.
In his work on the coronary circulation, James () noted that the LAD might supply varying degrees of the right ventricular free wall. He also noted that the right paraseptal region was supplied by the first big septal branches of the LAD alone or together with the conal branch of the right coronary artery (RCA) (the first artery branching from the proximal RCA). In 30% to 50% of cases in which no such conal branch was identified, a conal artery was observed originating from a separate ostium in the right aortic cusp. Recently, Said and Muhlberger (), described the “descending septal branch,” an artery originating from the first centimeter of the RCA, from the conal branch or from a separate ostium in the right aortic cusp. This artery originates from a segment in the RCA that is often free of atherosclerotic lesions, seldom developing atherosclerotic occlusions, and is thus, assumed to be an important source of collateral flow ([29, 30]). The difference between the “descending septal branch” and the artery we term the conal branch is probably just a matter of different nomenclature; for all practical purposes they are identical. Significant segment elevation in leads V1and V3R was found to be related to the presence of a small conal branch not big enough to reach the right paraseptal region. In the presence of a large conal branch reaching the IVS, no such ischemic changes in leads V1and V3R were noted.
3.5 Physiologic implications.
As shown by Indolfi et al. (), in cases where one coronary artery supplies areas of both the right and the left ventricle, severe hemodynamic disturbances may occur during ischemia related to that artery. Those disturbances occur as a result of the blood flow redistribution between different anatomic areas of the heart having different vascular resistances (). The compressive resistance exerted by the right ventricle is lower than that exerted by the left ventricle and the systolic coronary flow (expressed as a fraction of the diastolic flow) is significantly greater in blood vessels perfusing the right ventricle than in those perfusing the left ventricle (). During acute ischemia of the left ventricle, left ventricular end-diastolic pressure increases; this phenomenon does not occur in the right ventricle as its end-diastolic pressure does not increase during acute right ventricular ischemia (). As observed in the swine animal model where the LAD supplies areas of both the right and the left ventricle (), right ventricular “steal” may occur during acute ischemia caused by LAD stenosis in cases where this artery supplies areas of the right ventricle as well. In our study, by examining the admission ECG during the ischemic phase of anterior AMI, we were able to clearly identify patients with double circulation of the anterior IVS. In these patients the anterior IVS received its blood supply from the conal branch of the RCA together with the septal branches of the LAD (as evidenced by no ST segment elevation in lead V1). These patients were clearly differentiated from patients with common circulation of that area, which received its blood supply only from the septal branches of the LAD (as evidenced by significant ST segment elevation in lead V1). We assume that the presence of double circulation to the right paraseptal area (by the conal branch of the RCA and by septal branches of the LAD) protects that area from ischemic damage, thus preventing the occurrence of the right ventricular “steal” phenomenon and diminishing the left ventricular ischemic burden during anterior AMI.
This study indicates that significant ST segment elevation in lead V1during evolving anterior AMI is highly related to the presence of ST segment elevation in lead V3R and to the absence of a large conal branch reaching the IVS. No relation was found between ST segment elevation in lead V1during anterior AMI and the level of the LAD lesion site (proximal or distal to the first septal origin). We suggest that lead V1reflects the right side of the anterior IVS, receiving its blood supply from the conal branch together with the septal branches of the LAD (double circulation) or from those septal branches alone (common circulation). We think the clinical and prognostic significance of our findings is important for the correct stratification of patients with anterior AMI. Further prospective studies to clarify these assumptions are being carried out.
- acute myocardial infarction
- electrocardiogram, electrocardiographic
- interventricular septum
- left anterior descending coronary artery
- left anterior oblique
- right anterior oblique
- right coronary artery
- Statistical Analysis System
- Received June 27, 1996.
- Revision received October 31, 1996.
- Accepted November 12, 1996.
- The American College of Cardiology
- Wilkinson RS,
- Schaffer JA,
- Abildskov JA
- Castellanos A,
- Myerburg RJ,
- Kessler KM
- Tamura A,
- Kataoka H,
- Nagase K,
- Mikuria Y,
- Nasu M
- Schamroth L
- Birnbaum Y,
- Herz I,
- Solodky A,
- et al.
- Lopez-Sendon J,
- Coma-Canella I,
- Alcasena S,
- Seoane J,
- Gamallo C
- James TN
- Rodriguez MI,
- Anselmi CA,
- Sodi-Pallares D
- Sclarovsky S,
- Birnbaum Y,
- Solodky A,
- Zafrir N,
- Wurzel M,
- Rehavia E
- Said M,
- Muhlberger VA
- Indolfi C,
- Guth BD,
- Miyazaki S,
- Schulz R,
- Ross J Jr.
- Marcus ML
- Crottogini AJ,
- Guth BD,
- Barra JG,
- Willsham P,
- Lascano EC,
- Pichel RH