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(Circulation. 1996;93:1496-1501.)
© 1996 American Heart Association, Inc.
Articles |
From the Cardiovascular Division, Institute for the Prevention of Cardiovascular Disease, Deaconess Hospital, Harvard Medical School, Boston, Mass.
Correspondence to Francine K. Welty, MD, PhD, Institute for the Prevention of Cardiovascular Disease, 1 Autumn St, 5th Floor, Boston, MA 02215.
| Abstract |
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Methods and Results Between 1981 and 1989, 505 patients
underwent percutaneous transluminal coronary
angioplasty for post-MI ischemia at the Deaconess Hospital.
Long-term incidence (mean follow-up, 34 months) of death,
nonfatal reinfarction, repeated coronary angioplasty, and
coronary bypass surgery was determined for 479 patients and
then compared on the basis of the status of the artery, open versus
closed, at the end of angioplasty. The 5-year Kaplan-Meier actuarial
mortality rate was 4.9% for 456 patients with open infarct-related
arteries and 19.4% for 23 patients with closed infarct-related
arteries (P=.0008). Multivariate Cox
proportional hazards analyses controlling for age, sex, number
of diseased vessels, type and location of MI, and year of
coronary angioplasty revealed a hazard ratio for death for
closed compared with open arteries of 6.1 (95% CI, 1.8 to 20.0). Among
patients with ejection fractions <50%, a closed artery was associated
with a higher mortality (P=.0014) compared with patients
with open arteries. The status of the artery was not associated with a
difference in mortality in patients with ejection fractions
50%.
Conclusions An open artery after coronary angioplasty for post-MI ischemia is associated with significantly lower long-term mortality, particularly in patients with ejection fractions <50%.
Key Words: angioplasty ischemia mortality myocardial infarction
| Introduction |
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Most studies of the open artery hypothesis have compared patency of the infarct-related artery determined after thrombolytic therapy with long-term outcome; less attention has been focused on the prognosis of patients in whom open arteries are present after percutaneous transluminal coronary angioplasty (PTCA) for post-MI ischemia.26 27 28 29 30 31 32 33 Unfortunately, the number of patients in these studies has been too small to precisely delineate the outcome for patients with open versus closed vessels after revascularization in this setting.
To assess the effect of PTCA on subsequent death, nonfatal reinfarction, and the need for further revascularization procedures after MI complicated by ischemia, we obtained follow-up data on 479 patients with post-MI ischemia who underwent PTCA at the Deaconess Hospital (Boston, Mass) between 1981 and 1989. Long-term follow-up results were then compared on the basis of the status of the infarct-related vessel, open versus closed, at the end of the angioplasty procedure.
| Methods |
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The diagnosis of MI was based on the following criteria as previously described34 : chest pain >30 minutes in duration that was characteristic of MI, elevation of total creatine kinase level to at least twice the upper limit of normal, and a positive creatine kinaseMB band. Q-wave MI was classified as anterior or inferior on the basis of the presence of diagnostic Q waves in at least two precordial leads (anterior) or all three inferior leads or two inferior leads with T-wave changes (inferior). MI was classified as nonQ wave if ECG ST-segment and T-wave abnormalities were observed without progression to pathological Q waves. Two independent electrocardiographers examined serial ECGs. Recurrent ischemia was defined as recurrent angina >24 hours after the infarction or a positive exercise tolerance test before or within 3 months of hospital discharge.
Coronary Arteriography
The decision to perform PTCA was based on the presence of
70%
stenosis in the infarct-related artery and anatomy
suitable for angioplasty after visual review of an artery in at least
two orthogonal views. Patients with two- and three-vessel disease
and abnormal left ventricular function were included in the
study. Patients with prior coronary artery bypass surgery, left
main disease, or cardiogenic shock were excluded. Ejection fraction was
determined through planimetry of ventriculograms obtained at
angiography.
Coronary Angioplasty
PTCA procedural success was defined as one in which, on visual
inspection, >20% increase in luminal diameter was achieved with the
final diameter stenosis <50% and without occurrence of death,
acute MI, or the need for emergency bypass operation. Two independent
viewers assessed the angiographic films, and data were recorded
prospectively before any follow-up events occurred.
Peri-interventional acute MI was defined by new cardiac enzyme
elevation and/or new Q waves on the post-PTCA ECG. MI, requirement for
emergency bypass surgery, and death were classified as acute procedural
complications. Thrombolysis in Myocardial Infarction (TIMI)
definitions of perfusion were used.35 Grade 0 is complete
occlusion with no flow beyond the occlusion. Grade 1 is minimal
perfusion; contrast penetrates around the site of obstruction,
but minimal distal perfusion is present. Grade 2 is partial
perfusion characterized by a reduced rate of entry and clearance of
contrast into and out of the distal coronary bed. Grade 3 is
complete perfusion defined by normal entry and clearance rates of
contrast to and from the distal coronary bed. Arteries with
TIMI grade 0 flow after PTCA were classified as closed; those with
grade 2 or 3 flow were considered open. There were no arteries with
TIMI 1 flow after PTCA.
After dilatation, femoral arterial sheaths were left in place, and patients received aspirin and intravenous heparin for 12 to 24 hours. At the time of discharge, aspirin therapy was continued in patients in whom it was not contraindicated. ß-Blockers, calcium blockers, nitrates, and angiotensin-converting enzyme inhibitors were given in accord with standard therapy.
Long-term Follow-up
Long-term follow-up for recurrent angina, repeated
angioplasty, coronary artery bypass grafting, MI, or death was
accomplished through a questionnaire completed by the patient (n=347),
a telephone interview (n=105), or a chart review (n=27). Follow-up
for those patients who had died was obtained through a spouse,
offspring, or the referring doctor. The primary objective of this study
was not to identify restenosis; therefore, neither repeated
catheterization nor systematic treadmill testing was
used. However, the number of subjects who developed recurrent angina
necessitating repeated PTCA was determined.
Statistical Analysis
Results are expressed as mean±SD. Continuous variables were
compared with two-tailed unpaired t tests. Categorical
variables were compared by use of Fisher's exact test.
Long-term event-free survival for MI and death and the
composite outcomes of MI or death were estimated with the Kaplan-Meier
method. Open vessel differences were tested with a log rank test.
Multivariate analyses with a Cox proportional
hazards model adjusted for differences in age, sex, location and type
of MI, number of diseased vessels, and year of coronary
angioplasty were performed for each outcome to determine whether an
open artery was significantly related to recurrent event rates after
controlling for the covariates listed above. In each analysis,
the censoring date was considered to be the earliest date of the event
or the end of follow-up. Values of P<.05 were
considered significant.
| Results |
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Baseline Characteristics
Table 1
gives the baseline clinical characteristics
according to the status of the infarct-related artery after
angioplasty, open versus closed, for those patients in whom
follow-up was available. Table 2
gives the baseline
angiographic characteristics. Before PTCA, the infarct-related
arteries were open with critical stenoses in 423 patients
(84%) and totally occluded in 82 patients (16%). Ejection fraction
data were available in 284 subjects (60%; Table 2
). Those subjects for
whom ejection fraction was unavailable either had their initial
ventriculography performed at another hospital or did not have a
ventriculogram performed at catheterization.
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Long-term Follow-up
Long-term follow-up averaging 34 months was available in
456 of 463 patients (99%) with open arteries and all 23 patients with
closed arteries. At the end of follow-up (Table 3
),
there were 18 deaths (3.9%) among the 456 patients with open arteries
and 4 deaths (17.4%) among the 23 patients with closed arteries
(P=.0008). The actuarial 5-year mortality rates were 4.9%
and 19.4%, respectively (P=.0008). Follow-up was not
available for 7 patients, all of whom had open arteries. If we assume
that they had died, the mortality would increase from 4.9% to 5.4% in
the open artery group; this is still significantly different from the
mortality in the closed artery group.
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The 5-year actuarial event rates for nonfatal recurrent MI were 8.7% and 20.6% in the open and closed artery groups, respectively (P=.35). The 5-year actuarial event rates for reinfarction or death were 11.9% for patients with open arteries compared with 34.8% for those with closed arteries (P=.002). Patients with closed arteries had a higher rate of coronary bypass grafting (13.0%) in long-term follow-up compared with patients with open arteries (3.7%, P=.01). The 5-year actuarial rate for coronary bypass grafting was 4.8% for patients with open arteries compared with 22.3% for those with closed arteries (P=.01).
Fig 1
shows the 5-year Kaplan-Meier actuarial
event-free survival curves for death and the combined end points of
MI or death. Patients with open vessels had a significantly lower
mortality (P=.0008) and mortality or reinfarction
(P<.002) when tested with the log rank statistic.
Multivariate Cox proportional hazards analyses
controlling for age, sex, number of diseased vessels, type and location
of MI, and year of coronary angioplasty revealed a hazard ratio
for death for closed compared with open arteries of 6.1 (95% CI, 1.8
to 20.0), for the combined end point of MI or death of 3.7 (95% CI,
1.48 to 9.45), and for coronary bypass grafting of 4.0 (95%
CI, 1.11 to 14.74).
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The actuarial 5-year mortality rates in patients with ejection
fractions <50% were 2.6% in those with open arteries and 20.5% in
those with closed arteries (P=.0014). The actuarial 5-year
mortality rates in those with ejection fractions
50% were 5.6% and
7.7% in those with open and closed arteries, respectively
(P=.47). Fig 2
shows the 5-year Kaplan-Meier
actuarial event-free survival curves for mortality stratified by
ejection fractions <50% and
50%. In patients with ejection
fractions <50% and open vessels, mortality was significantly lower as
judged by the log rank statistic (P=.0014). In patients with
ejection fractions
50%, there was no difference in mortality in the
groups with open versus closed arteries.
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The presence of collaterals visualized at angiography before PTCA had no effect on outcome. The mortality in those with collateral vessels was 5.1% compared with 4.4% in those without collateral vessels (P=.838).
Restriction of the analyses to patients who did not receive thrombolytic therapy did not materially alter the results.
| Discussion |
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Several studies that used thrombolytic therapy without angioplasty support the contention that a patent infarct-related artery is associated with decreased mortality.14 15 16 17 In the Western Washington trial, patients were randomized to receive intracoronary streptokinase or placebo within 12 hours of the onset of acute MI.14 15 16 There was a striking association between infarct artery patency and a favorable 1-year mortality outcome. The death rate in the 80 patients with completely reperfused arteries was 2.5%, which was significantly lower than the 14.6% rate in those with occluded arteries (P=.008).
The most striking association between infarct-related artery patency and post-MI prognosis has been found in patients with low ejection fractions. Galvani et al24 followed 172 patients with single-vessel disease and first Q-wave MI, 58 of whom received thrombolytic therapy, for 43±30 months. The 10-year survival rate in patients with left ventricular dysfunction was 20% in those with TIMI grade 0 or 1 flow and 96% in those with TIMI grade 2 or 3 flow. All 16 deaths were in patients with left ventricular dysfunction defined as an end-systolic volume index >40 mL/m2. Galvani et al concluded that infarct-related artery patency was an independent predictor of survival after Q-wave MI in the presence of left ventricular dysfunction. Patients with normal left ventricular function had an excellent long-term prognosis, regardless of the patency status of the artery.
In another study, White et al25 demonstrated that
infarct-related artery patency was a predictor of improved
long-term survival (mean follow-up, 39±13 months) independent
of left ventricular function after
thrombolytic therapy in univariate and
multivariate analyses only when measured as an
occlusion score reflecting the amount of myocardium
supplied by an occluded artery. When the ejection fraction was
50%,
only occluded arteries supplying >25% of the left ventricle adversely
affected prognosis. If the ejection fraction was <50%, occluded
arteries supplying <25% of myocardium adversely affected
prognosis.25
An open artery also appears to be associated with improved survival in patients who do not receive thrombolytic therapy.19 20 21 Cigarroa et al19 studied patients with single-vessel disease who survived an acute MI and did not receive thrombolytic therapy. The 47-month mortality rate was 0% in 64 patients with partial or complete antegrade perfusion of the infarct-related artery compared with 18% in 115 patients with no or minimal antegrade perfusion. The left ventricular volumes and ejection fractions were similar in the two groups. Nine of the 16 patients with ejection fractions <40% and closed arteries died, whereas none of the 14 patients with ejection fractions <40% and open arteries died. Cigarroa et al concluded that in the presence of left ventricular dysfunction, a patent artery was the strongest predictor of survival.
Revascularization has been associated with improved survival compared with patients treated medically after MI. In 200 survivors of a first MI with single-vessel disease and no or minimal antegrade perfusion of the infarct-related artery, 16% of subjects treated medically died during a mean follow-up of 40±30 months compared with 2% of patients revascularized with PTCA or coronary bypass grafting.36 In a second study of 157 survivors of a first MI with an occluded infarct artery and stenoses of one or both remaining arteries, 46% of the 81 medically treated group died of cardiac causes during a mean follow-up of 62±35 months compared with only 18% of the 66 surgically treated patients.37 In these studies, healthier patients may have been referred for revascularization.
The current study is unique in that it assesses the prognostic significance of an open infarct-related artery after mechanical revascularization in the setting of a recent but not ongoing MI complicated by ischemia. Similar to prior studies, however, it supports the contention that a patent infarct-related artery carries independent prognostic benefit during long-term follow-up with regard to the incidence of mortality and nonfatal reinfarction. The results of the present study are relevant for the care of patients who have post-MI ischemia and suitable anatomy for revascularization. The results are not generalizable to all patients with MI or post-MI ischemia.
The benefit of an open infarct-related artery may be explained by several mechanisms. In the acute setting, normal antegrade blood flow limits infarct expansion and remodeling of the infarcted and noninfarcted zones and decreases ventricular dilatation.38 39 Decreased left ventricular dilatation in turn is associated with improved long-term prognosis.40 Infarct-related artery patency may also result in a reduction in ventricular arrhythmias.41 In the study of Cigarroa et al,19 all 21 deaths were sudden; therefore, these authors suggested that restoration of antegrade flow may decrease mortality through a mechanism independent of its influence on left ventricular function such as a diminution in electrical instability. Several studies have demonstrated that survivors of MI with open infarct-related arteries have a much lower incidence of signal-averaged ECG late potentials than survivors of MI with closed arteries.42 43 More recently, Boehrer et al44 have shown that the mechanical restoration of antegrade flow in survivors of MI with occluded infarct-related arteries causes such late potentials to resolve. Therefore, a large part of the beneficial effect of an open infarct-related artery may be its influence on electrical stability. Chronic patency may also be of value by providing a source for collateral flow.
No randomized trials have been conducted in patients with post-MI ischemia to determine whether revascularization of closed arteries with PTCA versus continued medical therapy for sustained occlusion reduces subsequent MI and death. Because revascularization often is required to alleviate the symptoms of post-MI ischemia, it is not possible to perform a randomized trial in patients with this clinical syndrome. Therefore, the conclusions, which are based on results observed in groups such as those described in the present study in which the outcome of those patients with closed versus open arteries was compared, may have important implications for clinical management.
In summary, the results of the present study indicate that successful revascularization with PTCA after MI complicated by ischemia is associated with decreased mortality, particularly in patients with ejection fractions <50%. These findings, considered together with numerous reports indicating a strong association between a favorable outcome and a patent infarct-related artery after thrombolytic therapy, further support the need, as suggested by Hillis and Lange,45 for a randomized trial to determine whether revascularizing occluded coronary arteries 48 hours or longer after MI, even in the absence of recurrent ischemia, reduces the occurrence of reinfarction and death.
Received August 23, 1995; revision received October 25, 1995; accepted November 3, 1995.
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