Prognostic Significance of Precordial ST-Segment Changes in Acute Inferior Wall Myocardial Infarction

Prognostic Significance of Precordial ST-Segment Changes in Acute Inferior Wall Myocardial Infarction* Tetsuro Sugiura, MD, FCCP; Yo Nagahama, MD; Kazuya Takehana, MD; Nobuyuki Takahashi, MD; and Toshiji lwasaka, MD, FCCP

Study objective: To examine the clinical significance of precordial ST-segment changes in patients with acute Q-wave inferior wall myocardial infarction. Design: Prospective evaluation (clinical follow-up) of Q-wave inferior wall myocardial infarction over a 6-year period in patients who fulfilled the inclusion criteria. Setting: Coronary care unit at a university hospital. Patients: Two hundred consecutive patients with acute Q-wave inferior wall myocardial infarction admitted to the coronary care unit within 24 h from the onset of chest pain. Measurements and results: Precordial ST-segment depression resolved <24 h (transient) after admission in 84 patients, lasted 2:24 h (persistent) in 48 patients, and was absent in 68 patients, while ST-segment elevation in V4 a was detected in 60 patients. Seventy-one patients had major in-hospital complications and 18 patients died in the hospital. When nine variables were used in the multivariate analysis, right ventricular dilatation and persistent precordial ST-segment depression were the important factors related to major in-hospital complications, whereas age, alveolar arterial oxygen difference, and persistent precordial ST-segment depression were important for in-hospital deaths. Conclusion: Left ventricular posterior wall involvement, diagnosed by persistent precordial ST-depression, was an independent and stronger predictor of major in-hospital complications and deaths than right ventricular involvement in patients with acute Q-wave inferior wall myocardial infarction. (CHEST 1997; 111:1039-44) Key words: acute myocardial infarction; echocardiogram; electrocardiogram

Although patients with acute inferior wall myocardial infarction who demonstrate ST-segment depression in the precordial leads have larger infarct size and complication rate similar to those with anterior wall myocardial infarction,1- 5 precordial changes commonly resolve quickly and transient precordial ST-segment depression (resolved <24 h) is not a specific marker for posterior wall involvement.2·4 Therefore, it is important to distinguish between transient and persistent (lasting ~24 h) precordial ST-segment changes when evaluating their clinical significance. However, to our knowledge, none of the studies have differentiated transient and persistent precordial ST-segment depressions in evaluating their prognostic significance. However, right ventricular infarction contributes markedly to hemodynamic instability and increased *From The Second Department of Internal Medicine , Kansai Medical University, Osaka, Japan. Manuscript received February 7, 1996; revision accepted Octobe r 7. Reprint requests: Dr. Sugiura, MD, CCU, Kansai Medical University, 10-15 Fumizono-cho, Moriguchi City, Osaka 570, Japan

in-hospital mortality in patients with inferior wall myocardial infarction.6 -9 Moreover, right ventricular involvement during acute inferior myocardial infarction can be diagnosed accurately by ST-segment elevation in the right precordialleads. 10•11 This study was designed to evaluate the relative importance of ST-segment changes (precordial ST-segment depression and ST-segment elevation in V 4 R) among seven other clinical factors in predicting hospital course in patients with their first acute Q-wave inferior wall myocardial infarction.

MATERIALS AND METHODS

Patients We studied 200 consecutive patients (aged 31 to SO years ) with a Q-wave inferior wall myocardial infarction over a 6-year period who fulfilled the following criteria: (1) admitted to the coronary care unit within 24 h from the onset of chest pain and survived the first 24 h after admission; ( 2) no history of myocardial infarction or chronic lung disease; and (3) sinus rhythm without interventricular conduction defects. Patients were enrolled in this CHEST I 111 I 4 I APRIL, 1997

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study at the point when definite diagnosis of myocardial infarction was made. During this study period, a technically satisfactory echocardiogram could not be obtained in 17 patients, and they were not included in this study. Clinical Evaluation

The diagnosis of myocardial infarction was made when the patients had ST elevation with new Q waves (II, Ill and aVF) on setial ECGs, and at least twice the normal elevation in serum creatine kinase value with MB isoenzyme ~5%. ECGs were taken at the time of admission and at least at 8-h intervals for the first 3 days after admission. At least 1 mm of ST-segment elevation and QS or QR in right precordial lead (V4 R) at the time of hospital admission and observed ~24 h were considered diagnostic of right ventricular infarction. 10 At least 1 mm of ST-segment depression 80 ms after the J point in any two or more of leads V1 , V2 , or V3 recorded on admission and observed ~24 h after the admission was considered diagnostic of persistent precordial ST-segment depression. A history of hypertension was defined as antihypertensive therapy previously prescribed, more than twice previous documented diastolic readings over 95 mm Hg, or more than twice previous systolic readings over 160 mm Hg. Patients were divided into current smokers, history of smoking, and nonsmokers (who had never smoked). Patients were defined as having noninsulin-dependent diabetes mellitus if diabetes (of adult-onset variety) had been documented and therapy initiated before the onset of myocardial infarction. Arterial blood was taken from radial or femoral arteries at the time of admission with the patients breathing room air. The alveolar arterial oxygen difference was calculated by assuming a respiratory quotient equal to 0.8. Careful auscultation was performed at least twice daily in all patients and more frequently in patients presenting with pleuritic chest pain or any other recurrent chest pain. Pericardia! rubs were considered to be to-andfro, scratchy, grating, or creaking in quality. Identification of pericardia! rub was based on nonconformity with the characteristic locations, radiations, and respiratory responses of most murmurs and thrills. Pericardial rub was considered present only after it was independently diagnosed by more than two cardiologists who were unaware of the ECG findings. Major in-hospital complications included ventricular fibrillation, sustained ventricular tachycardia, cardiogenic shock (systolic BP <90 mm Hg \vith signs of impaired peripheral circulation), and third-degree atrioventricular block or sinus arrest requiring temporary cardiac pacing during the first 3 days after hospital admission. Echocardiography

Two-dimensional and M-mode echocardiography were performed (with an SSD 870 phased-array sector scanner; Aloka; Tokyo). All standard views were recorded on videotape for subsequent analysis by observers who were unaware of the patients' clinical data. Left ventricular wall motion was assessed by two-dimensional echocardiography using 11 segments obtained by long- and short-axis images, and the severity of abnormal wall motion was diagnosed by visual assessment of wall thickening and endocardial movement during systole. 12 The number of segments with advanced asynergy (akinesis or dyskinesis) was determined. Abnormal wall motion in the posterior wall was defined as presence of advanced asynergy in the posterior base and posterior midsegments. 12 The abnormal motion of the right ventricular wall (inferior wall and free wall) was diagnosed using parasternal long- and short-axis views and apical and subcostal four-chamber views of the two-dimensional echocardiogram.13 Right ventricular wall was categorized as abnormal 1040

(akinesis or dyskinesis) or normal. Right ventricular dilatation was considered present when the end-diastolic diameter ratio between the right and left ventricle was >0.5 in both parasternal long- and short-axis views at the papillary muscle level obtained from parasternal transducer position in the supine position. 13 Akinetic or paradoxic septal motion was categorized as abnormal. The absence of anatomic shunt in the heart was confirmed by Doppler echocardiogram. Coronary Arteriography

A coronary atteriogram was performed before the hospital discharge in 157 patients. Forty-three patients did not have coronary atteriography because 18 patients died in the hospital and 25 patients refused to have angiography. Angiograms were analyzed by staff cardiologists who were unaware of the ECG findings. The patency of the infarct-related artery was assessed according to the Thrombolysis in Myocardial Infarction criteria. 14 Patients with partial and complete anterograde perfusion were considered to have patent infarct-related coronary artery. To evaluate the effect of disease on the noninfarcted regions, the presence of left anterior descending artery lesions was evaluated. Coronary artery lesions with ~70% reduction in diameter were considered obstructive. Informed consent was obtained from each patient before the study. Statistical Analysis

Results are reported as mean±SD. A Student's t test was used for quantitative data and Fisher's Exact Test was used for qualitative data. Statistical analysis among the three groups was performed by x2 analysis followed by Scheffe's type multiple comparison method. Discriminant analysis (stepwise forward selection method) (using Data Analyzing System version 4) was performed to evaluate the important variables related to major in-hospital complications and mortality. A p value <0.05 was considered significant.

RESULTS

Incidence of Precordial ST-Segment Depression Among the 200 patients with acute Q-wave inferior wall myocardial infarction, precordial ST-segment depression was detected in 132 patients on admission and was absent in 68 patients (Table 1). Of the 132 patients with precordial ST -segment depression, ST-segment depression resolved <24 h (transient) in 84 patients and lasted 2:24 h (persistent) after admission in 48 patients. There were no significant differences among the three groups (persistent, transient, and no precordial ST-segment depression) in the incidence of hypertension (35%, 36%, and 38%, respectively; p=0.93) and diabetes mellitus (21 %, 18%, and 19%, respectively; p=0.92). Ninetythree patients were nonsmokers, 10 patients had a history of smoking, and 97 patients were current smokers. There were no significant differences in the incidence of nonsmokers among the three groups (48%, 43%, and 50%, persistent, transient, and no precordial ST-segment depression, respectively; Clinical Investigations in Critical Care

Table !-Incidence of Major In-Hospital Complications and Deaths in Patients With Precordial ST-Segment Depression* Complications Absent ST depression N T p p value N vs T N VS p T vs P

Present

56 57 16

12 27 32 p=0.18 p<0.001 p<0.001

Table 2-In-Hospital Complications* In-Hospital Complications

Mo1tality Survivors

Nonsurvivors

65 80 37

3 4 11 p=0.99 p=0.0027 p=0.0021

*Values are mean:!:SD. N=none; P=persistent; T =transient.

p=0.917). Eighty-six patients received reperfusion therapy (percutaneous transluminal coronary angioplasty or percutaneous transluminal coronary recanalization) at the time of admission. There were no significant differences in the incidence of reperfusion therapy among the patients with persistent (42%), transient (51%), and no (34%) precordial ST-segment depression (p=0.097). Seventy-one patients had at least one of the major in-hospital complications, and 18 patients died in the hospital. Although there were no significant differences in the incidence of major in-hospital complications and hospital deaths between patients with transient and those without precordial ST-segment depression, patients with persistent ST-segment depression had significantly higher incidence of major in-hospital complications and deaths than those with transient and no precordial ST-segment depressions. In-Hospital Complications Patients with major in-hospital complications had significantly higher mean age, more left ventricular segments with advanced asynergy, higher incidence of posterior wall asynergy, septal asynergy, and pericardia! rub, and larger alveolar arterial oxygen difference than those without major in-hospital complications (Table 2). However, there was no significant difference in the incidence of major in-hospital complications between patients with and without reperfusion therapy (32% and 38%, respectively). None of the patients had wall motion abnormality in the anterior segments. Right ventricular dilatation was observed in 33 patients and all the patients with right ventricular dilatation had abnormal inferior right ventricular wall motion. A significantly higher incidence of right ventricular dilatation was observed in patients with major in-hospital complications than those without. ST-segment elevation in v4R was detected in 60 patients. The patients with major

Age, yr Asynergic segments Posterior asynergy Septal asynergy RV dilatation P(A-a)0 2 Pericardia] rub ST elevation in v4R Persistent STD

Present (n=7l)

Absent (n=129 )

p Value

67:!::11 3.1:!::1.6 42 (59) 22 (31) 23 (32) 40:!::11 17 (24) 33 (46) 32 (45)

63:!::11 2.2:!:: 1.4 36 (28) 10(8) 10 (8) 34:!::12 15 (12) 27 (21) 16 (12)

0.015 <0.001 <0.001 < 0.001 <0.001 <0.001 0.038 <0.001 <0.001

*Values are mean:!:SD or No. (%). P(A-2)0 2 =alveolar-arterial oxygen difference; NS=not significant; RV=right ventricular; STD=precordial ST-segment depression.

in-hospital complications had significantly higher incidence of ST-segment elevation in V4 R (p and persistent precordial ST-segment depression) were used in the discriminant analysis to determine the important variables predicting major in-hospital complications, right ventricular dilatation and persistent precordial ST-segment depression were found to be the significant factors related to major inhospital complications (F[4, 195]) (Table 3). Predictive accuracy was 0.72. Although the incidence of ventricular fibrillation and sustained ventricular tachycardia did not differ among the patients with persistent, transient, and no precordial ST-segment depression (21 %, 13%, and the 13%, respectively; p=0.43), the incidence of cardiogenic shock (29%, 8%, and 7%, respectively) and need for tempormy pacing (33%, 10%, and 15%, respectively) were significantly higher in patients with persistent precordial ST-segment depression than those with transient (p=0.003 and p=0.002,

Table 3-Important Factors Related to In-Hospital Complications*

Constant RV dilatation Persistent STD

Discriminant Coefficient

F Value

p Value

3.94 -1.60 -1.62

10.61 13.71

0.0003 0.0013

*Stepwise forward selection method. Abbreviations as in Table 2. CHEST I 111 I 4 I APRIL, 1997

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shock and temporary pacing, respectively) and no precordial ST-segment depression (p=0.003 and p=0.031, respectively). In-Hospital Mortality Eighteen patients died in the hospital (pump failure-nine patients with persistent, three patients with transient, and three patients with no precordial ST-segment depression; ventricular rupture-two patients with persistent precordial ST -segment depression; and ventricular fibrillation-one patient with transient precordial ST-segment depression) (Table 4). There was no significant difference in the incidence of in-hospital mortality between patients with and v.rithout reperfusion therapy (7% and 10%, respectively). Patients who died in the hospital were older, had significantly more left ventricular segments with advanced asynergy, higher incidence of posterior wall asynergy, and larger alveolar arterial oxygen difference than those in the survivors. Among the 18 patients who died in the hospital, lO patients had ST-segment elevation in V4R and 11 patients had persistent precordial ST-segment depression. Patients who died in the hospital had significantly higher incidence of ST-segment elevation in V4H or persistent precordial ST-segment depression than the survivors. When nine variables were used in the multivariate analysis, age, alveolar arterial oxygen difference, and persistent precordial ST-segment depression were found to be the important factors related to in-hospital mortality (F[3, 196], degree of freedom for F test) (Table 5). Predictive accuracy was 0.77. Coronary Angiogram A coronaty arteriogram was obtained from 32 patients (67%) with persistent, 67 patients (80%) with transient, and 58 patients (85%) with no precordial ST-segment depression. Right coronary artery was infarct-related artery in 117 of 157 patients

Table 4-In-Hospital Deaths*

Age, yr Asynergic segments Posterior asynergy Septal asynergy RV dilatation P(A-2)0 2 Pericardia! rub ST elevation in V4 R Persistent STD

Survivors (n=182)

Non survivors (n =l8)

p Value

64::'::11 2.4::':: 1.6 66 (36) 26 (14) 28 (15) 35::'::11 26 (14) 50(27) 37 (20)

71::'::9 3.6::'::1.0 12 (67) 6 (33) 5 (28) 47::'::11 6(33) 10(56) 11 (61)

0.009 0.002 0.023 0.077 0.309 <0. 001 0.077 0.027 <0.001

*Values are mean::':SD or No. (%). Abbreviations as in Table 2.

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Table 5-Important Factors Related to In-Hospital Deaths*

Constant Age P(A-2)0 2 Persistent STD

Discriminant Coefficient

F Value

p Value

7.70 -0.05 -0.09 -2.02

4.26 13.59 9.81

0.0402 0.0003 0.0020

*Stepwise forward selection method. Abbreviations as in Table 2.

(75%). Patients with precordial ST-segment depression had significantly higher incidence of circumflex infarct-related artery than those without precordial ST-segment depression (31% and 16%, respectively; p=0.036), but no significant difference was observed between patients with transient and persistent precordial ST-segment depressions (31% and 31%, respectively). There were no significant differences in the incidence of patent infarct-related artery among the three groups (38%, 55%, and 48%, persistent, transient, and no precordial ST -segment depression, respectively; p=0.162). Fifteen patients with persistent, 19 patients with transient, and 18 patients with no precordial ST-segment depression had associated lesions in the left anterior descending artery; there were no significant differences among the three groups. Coronary arte1iogram was obtained from 43 patients (72%) with ST-segment elevation in v4R' Twenty patients (47%) with ST-segment elevation in v4R had patent infarCt-related artery and 15 patientS (35%) had associated lesions in the left anterior descending artery; the difference was not significant compared to those with persistent precordial STsegment depression.

DISCUSSION

ST-segment depression in the precordial leads in patients with acute inferior wall myocardial infarction are reported to be associated with larger infarct size and more complicated clinical course than in patients without these findings. 1 -5 However, in a high proportion of patients, ST-segment depression in the precordial leads resolves quickly, and transient precordial ST-segment depression is not a specific marker for posterior left ventricular wall involvement.2·4 In this study, despite no significant differences in the incidence of patent infarct-related artery and left anterior descending artery lesions between the patients with transient and persistent precordial ST-segment depression, we found that patients with persistent precordial ST -segment depression had higher incidence of major in-hospital complications and deaths. However, the risk of Clinical Investigations in Critical Care

having major in-hospital complications and deaths in patients with transient precordial ST-segment depression was identical to those without precordial ST-segment depression. Major In-Hospital Complications A significantly higher incidence of persistent precordial ST-segment depression and ST-segment elevation in V4R was found in patients with major in-hospital complications compared to those without them. However, when the two ECG criteria (persistent precordial ST-segment depression and ST-segment elevation in V4R) were evaluated with seven other clinical variables, we found that persistent precordial ST -segment depression was an independent ECG sign of major in-hospital complications, but the relative importance of ST-segment elevation in v4R WaS lOW. ECG evidence of ST-segment elevation in the right precordial leads has been shown to be both sensitive and specific for right ventricular infarction,10.1 1 but the clinical outcome of right ventricular infarction vmies widely. Of the patients with STsegment elevation in V4R , we have found that those with right ventricular dilatation had more left ventricular asynergic segments and higher incidence of septal asynergy compared to those without right ventricular dilatation. 15 Therefore, it is not surprising to find that right ventricular dilatation was one of the important predictors of major in-hospital complications because they are associated with larger left ventricular infarct size. There is a greater degree of myocardial shortening in the left ventricular minor axis and approximately 87% of the stroke volume is reported to be generated by shortening of the left ventricular minor axis.16 Therefore, more impairment of left ventricular function is observed when the infarct zone is extended to the mid and base of the posterior wall following inferior myocardial infarction. An earlier report from our laboratory found that persistent precordial ST segment depression was not only a specific indicator of concomitant posterior involvement with severe wall motion abnormality but was also associated with higher incidence of infarction-associated pericarditis.4 Patients with anatomically transmural infarction of the posterior wall have extension to the epicardial surface; this is responsible for producing pericardia! inflammation of the infarct zone, regardless of wall motion abnormality. Therefore, considering the results of multivariate analysis, transmurality of infarction of the posterior segments, expressed by persistent precordial ST -segment depression, was an important factor related to higher incidence of major in-hospital complications.

In-Hospital Mortality Alveolar-arterial oxygen difference was found to be one of the independent predictors of in-hospital deaths. An earlier report from our laboratory has indicated that alveolar-arterial oxygen difference had the best correlation with infarct sizeJ7 Although decreased arterial oxygen tension could be compensated by an increase in cardiac output to maintain oxygen delivery to the tissue, this compensatory mechanism could not have operated in the patients with restricted cardiac output as a result of extensive myocardial damage extending to the posterior segments. Furthermore, an increase in the incidence of in-hospital deaths with advanced age was found. Higher incidence of in-hospital deaths in the elderly may be related to a higher incidence of coexisting pathologic changes in the noninfarcted myocardium, which could contribute to left ventricular pump failure . One explanation for the difference in the mortality rate among patients with inferior wall myocardial infarction is a heterogeneous clinical entity with clinical outcome dependent on whether posterior left ventricular segments or the right ventricle is also involved. In this study, we found that persistent precordial ST -segment depression was an important clinical variable related to in-hospital mortality. As the incidence of left anterior descending artery lesions in patients with persistent precordial ST -segment depression was not significantly higher than the incidence in those with transient precordial ST -segment depression or those with ST-segment elevation in V4R, ischemia of the anterior wall could not have had a significant effect on the in-hospital mortality. Therefore, in addition to advanced age and disturbance of pulmonary gas exchange resulting from more extensive myocardial damage, the localization of the infarct zone is another independent prognostic indicator in patients with acute Q-wave inferior wall myocardial infarction.

CONCLUSION

Involvement of posterior segments, diagnosed by persistent precordial ST-segment depression, was an independent predictor of major in-hospital complications and deaths.

REFERENCES

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