CLINICAL STUDY
Time course and determinants of left ventricular function recovery after primary angioplasty in patients with acute myocardial infarction
Imad Sheiban, MD*,
Gabriele Fragasso, MD ,
Giuseppe M. C. Rosano, MD ,
Aniruddha Dharmadhikari, MD,
Vaios Tzifos, MD,
Paolo Pagnotta, MD,
Sergio L. Chierchia, MD, FESC, FACC and
Gianpaolo Trevi, MD*
* Department of Internal Medicine, Division of Cardiology, University of Torino, Torino, Italy
Department of Cardiology, Istituto Scientifico/Università San Raffaele, Milano, Italy
Cardiovascular Research Unit, San Raffaele–Roma, Tosinvest Sanita’, Roma, Italy
Manuscript received August 7, 2000;
revised manuscript received April 19, 2001,
accepted April 27, 2001.
Reprint requests and correspondence: Dr. Imad Sheiban, Department of Internal Medicine, Division of Cardiology, Interventional Cardiology Laboratory, University of Torino, Ospedale San Giovanni Battista "Molinette," I-10126 Torino, Italy
isheiban{at}yahoo.com
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Abstract
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OBJECTIVES
We sought to evaluate the importance of time in relation to treatment, time course and determinants of recovery of left ventricular (LV) function in patients with acute myocardial infarction (AMI) undergoing primary percutaneous transluminal coronary angioplasty (PTCA).
BACKGROUND
Myocardial salvage has been shown to be dependent on the time elapsed from the onset of AMI to reperfusion.
METHODS
Left ventricular function was evaluated at hospital admission, after angioplasty, at 24 h and 6 months by both echocardiography and angiography and at 1, 7, 30, 90 and 180 days by echocardiography in 101 consecutive patients.
RESULTS
Patients were allocated to three groups according to interval between symptom onset and angioplasty: <2 h (group A), 2 to 4 h (group B) and >4 h (group C). Patients in groups A and B showed a progressive improvement of LV function between day 7 and day 90, which became statistically significant at day 30 (p < 0.01). No LV function changes were noted in group C patients. Thrombolysis In Myocardial Infarction (TIMI) flow grade <3 at 24 h was not associated with any significant change in LV volume and function during the six-month follow-up period. Restenosis, when associated with TIMI flow grade 3 in the infarct-related vessel, did not influence LV function. Flow grade <3 of the infarct-related artery was not associated with any improvement of cardiac events independently from the time to treatment at the initial procedure.
CONCLUSIONS
Patients undergoing primary PTCA for AMI have a good recovery of LV function if TIMI flow grade 3 is restored within 4 h. Coronary angioplasty limits further remodeling of the LV in patients treated after 4 h.
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Abbreviations and Acronyms
| | AMI | = acute myocardial infarction | | ANOVA | = analysis of variance | | CK | = creatine kinase | | IRA | = infarct-related artery | | LV | = left ventricular | | PTCA | = percutaneous transluminal coronary angioplasty | | TIMI | = Thrombolysis In Myocardial Infarction | | WMSI | = wall motion score index |
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Early restoration of patency of the infarct-related artery (IRA), either by primary percutaneous transluminal coronary angioplasty (PTCA) or by thrombolysis, improves patient survival by reducing the infarct size and preserving left ventricular (LV) function (1–13). Most reperfusion studies have shown a direct relationship between time to treatment and preservation of LV function and improvement of patient survival (2,9). However, some studies have also documented a beneficial effect of late opening of the IRA (10–13). The question arises as to whether there exists a time limit for reperfusion therapy in patients with an evolving acute myocardial infarction (AMI). Although it has been shown that PTCA is effective in reducing mortality in patients with AMI, there are presently few reports to suggest a time-dependent effect of primary PTCA on LV function and the time course of the maximal possible recovery of LV function.
The aims of the present study were to evaluate the importance of the time to treatment on the recovery of LV function and to compare it with the fate of the IRA in a consecutive, unselected series of patients with an evolving AMI undergoing PTCA.
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Methods
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Study group.
The study group included 108 consecutive patients with AMI who underwent primary PTCA within 12 h from symptom onset and within 1 h from their arrival in the emergency department. None of them had received thrombolytic therapy before angioplasty. Complete angiographic and echocardiographic follow-up studies were available in 101 patients, and these patients were included in the present study. Criteria for primary angioplasty were presentation within 12 h from symptom onset, electrocardiographic evidence of evolving AMI (>1 mm ST segment elevation in two or more contiguous limb leads or ST segment elevation >2 mm in the precordial leads) and the ability of the patient to give written, informed consent.
Angioplasty protocol.
After providing written, informed consent, the patients were transferred immediately to the catheterization laboratory. In general, the procedure was started within 1 h of the arrival of patient to the emergency room. Unless contraindicated, routine pre-medications consisted of intravenous heparin (1,000 U/h), aspirin (325 mg orally) and intravenous nitroglycerin (7 to 8 µg/kg body weight per h). The angiographic protocol was started with left ventriculography, followed by coronary angiography. Coronary angioplasty was performed only on the IRA. Intravenous heparin was continued (1,000 U/h) for at least 24 h after the procedure. Procedural success was defined as residual stenosis <30%, without major complications (death or urgent coronary artery bypass graft surgery). All patients underwent an angiographic control study within 36 h. Heparin was then stopped, and the sheaths were removed when the activated clotting time dropped <160 s. All patients were maintained on aspirin (325 mg/day) and beta-blockers, calcium antagonists and oral nitrates, either alone or in combination, together with angiotensin-converting enzyme inhibitors. Cardiac enzymes were obtained every 8 h for at least 48 h after angioplasty. Before hospital discharge, echocardiography was performed. Patients with worsening angina, reinfarction or other cardiac events before discharge underwent repeat catheterization.
Evaluation of LV function.
Left ventriculography was performed (in the 30° right anterior oblique orthogonal projection) before coronary angiography, after PTCA, and was repeated at 24 h and 6 months after PTCA. Left ventricular volumes were calculated by the area–length method. Echocardiography was performed at hospital admission, soon after PTCA and at 1, 7, 30, 90 and 180 days after PTCA, using a phased-array electronic ultrasound system (Sonos 2500, Hewlett-Packard, Andover, Massachusetts). Images were recorded on VHS videotape, and end-diastolic and end-systolic frames were selected from three standard apical views. Volumes were calculated by the biplane area–length method. The LV was divided into 16 segments (14). For each segment, systolic wall motion and thickening were visually graded with the following semiquantitative scoring system: 1 = normal or hyperkinesia; 2 = hypokinesia; 3 = akinesia; and 4 = dyskinesia. Left ventricular wall motion score index (WMSI) was derived using the sum of the individual scores divided by the total number of analyzed segments. Experienced investigators, who had no knowledge of the clinical and angiographic data, analyzed the left ventriculograms and echocardiograms.
Follow-up.
All patients underwent a six-month angiographic control study. Patients with evidence of recurrent ischemia underwent repeat cardiac catheterization, followed by a new revascularization procedure (mechanical or surgical) if needed. The mean period of follow-up was 32.7 ± 13.3 months. All patients underwent echocardiography at each follow-up visit.
Statistical analysis.
Data are presented as the mean value ± SD or as percentages where appropriate. Baseline clinical differences were analyzed using the unpaired the t test. To compare proportions, either the chi-square test or, when appropriate, the Fischer exact test was used. Two-way (time-group) repeated measures analysis of variance (ANOVA) was used to test differences between the groups for the evolution, across time, of continuous variables. The data for which ANOVA was used are presented in each case as follows: p value for treatment by period interaction effect; p value for treatment effect; and p value for period effect. Linear regression analysis was performed to evaluate the relationship between LV ejection fraction and cardiac enzyme release. A p value <0.05 was considered significant. Statistical analysis was performed using the Statview 4.5 software program (SAS Institute, Cary, North Carolina).
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Results
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The baseline clinical and angiographic characteristics of patients are described in Tables 1 and 2. The patients were allocated to three groups according to the time between symptom onset and primary PTCA: <2 h (n = 24, group A); 2 to 4 h (n = 32, group B); and >4 h (n = 45, group C). The three groups were comparable in terms of clinical characteristics and the use of cardiac medications during and after the procedure. The procedural success rate was 100%. The majority of patients from group C (n = 32, 71%) were reperfused within 6 h from symptom onset. Patients from the three groups had comparable clinical and angiographic characteristics and infarct size.
Cardiac enzymes.
Peak levels of cardiac enzymes were comparable in all three groups. However, the time to peak cardiac enzymes release was significantly higher in group C than in groups A and B (16 ± 3 vs. 7 ± 5 and 9 ± 4 h, respectively, p < 0.001) (Fig. 1).
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Figure 1 Peak and time to peak creatine kinase (CK) and CK-MB levels in the three study groups after reperfusion.  p < 0.001.
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No major complications occurred during the procedure or during the hospital period in any patient. During the hospital period, one patient from group B had recurrence of angina and underwent repeat PTCA. Three patients (one from each group) had minor bleeding not requiring blood transfusion.
Left ventricular function.
Pre-procedural LV volumes and ejection fractions, as well as WMSI, were comparable in the three groups. After the procedure, the patients in groups A and B showed a significant and progressive reduction in LV volume (Fig. 2) and progressive improvement of LV ejection fraction between day 1 and day 180 (0.42 ± 0.04 vs. 0.43 ± 0.03; ANOVA: p < 0.0001 for treatment by period interaction effect, p < 0.0073 for treatment effect and p < 0.0001 for period effect), whereas no significant difference in LV function was noted during the first seven days (0.42 ± 0.02 and 0.43 ± 0.03 vs. 0.44 ± 0.03 and 0.45 ± 0.04, p = NS for groups A and B at day 1 vs. day 7) and between three and six months (0.51 ± 0.04 and 0.52 ± 0.03 vs. 0.52 ± 0.04 and 0.51 ± 0.04, p = NS for groups A and B at 3 vs. 6 months) (Fig. 3). A significant decrease in WMSI was noted in these two groups of patients (ANOVA for group A: p < 0.0001 for treatment by period interaction effect, p < 0.0081 for treatment effect and p < 0.0001 for period effect; ANOVA for group B: p < 0.0001 for treatment by period interaction effect, p < 0.0084 for treatment effect and p < 0.0001 for period effect) (Fig. 4).
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Figure 2 Changes in left ventricular diastolic and systolic volumes in all study groups during the follow-up period.
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Figure 3 Changes in left ventricular ejection fraction in all study groups during the follow-up period.
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No difference in improvement of LV function and regional wall motion abnormalities was found according to the location of the IRA. In these patients, no significant relationship was found between the degree of LV function recovery and cardiac enzymes release (Fig. 2), nor between cardiac enzymes release and increase in ejection fraction (r = 0.20, p = NS).
Patency of the IRA and LV function.
Post-procedural slow flow (TIMI flow grade <3) occurred in 12 patients. This phenomenon was more frequently observed in patients treated after 2 h from symptom onset (1 patient from group A vs. 11 patients from groups B and C, p < 0.001). At the 24-h angiographic control study, the patients’ slow flow was still present in all 11 patients from groups B (n = 4) and C (n = 7) (Table 3). Improvement of LV function at follow-up was not present in any patient showing slow flow at 24 h independently from the time to treatment (Table 4).
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Table 3 Six-Month Follow-Up of Left Ventricular Ejection Fraction in Patients With TIMI Flow Grade <3 at 24-h Angiography
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Angiographic restenosis was noted in 32 patients (32%) at the six-month follow-up. The incidence of restenosis was comparable between the three groups: 8 patients (33%) from group A; 10 patients (31%) from group B; and 14 patients (32%) from group C (Table 5). Restenosis had no impact on recovery of LV function, unless it resulted in TIMI flow grade <3 in the IRA (Tables 5 and 6). Individual analysis of LV function and clinical follow-up of the 17 patients who had restenosis associated with TIMI flow grade <3 in the treated vessel showed no improvement of LV function and volume in these patients, independently from the time to treatment. Clinical events, including death and congestive heart failure during long-term-follow-up, were more frequent in patients who had total reocclusion or TIMI flow grade 1 in the IRA, independently from the time to treatment (Table 6).
At a mean follow-up duration of 32.7 ± 13.3 months, the target lesion revascularization rate, as well as mortality, were similar in all three groups. Cardiac death occurred in three patients (2.9%). All three patients had a total reocclusion of the IRA at six-month angiographic follow-up.
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Discussion
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The present study shows that primary PTCA for patients with AMI is effective in improving LV function if performed within 4 h from symptom onset. Nevertheless, even late recanalization, after 4 h, of the IRA appears effective in preventing LV enlargement and remodeling. Our data show that very early reperfusion (<2 h) with primary PTCA was associated with low early and in-hospital, as well as long-term follow-up, clinical events. Patients who were reperfused within 4 h show similar results. Also, LV function recovery, monitored during follow-up, was similar in patients treated within 4 h from symptom onset. Interestingly, improvement of LV function variables became apparent only seven days after the procedure, reaching statistical significance at 30 days and progressively continuing until the third month after reperfusion. No further significant improvement was observed beyond this time. In patients reperfused after 4 h, no significant LV function changes were observed during follow-up (Table 3, Fig. 2, 3 and 4). However, as shown in Figures 2, 3 and 4,, these variables did not worsen during follow-up, indicating that the expected post-infarction remodeling did not occur in group C.
Our data also show that there were no differences in peak levels of cardiac enzymes among the three groups, although the time to peak cardiac enzymes was significantly longer in patients reperfused late, as compared with those reperfused early (Fig. 1). Restenosis affected the recovery of LV function only when flow in the IRA was <3 (TIMI grade), and this relationship was independent of the time to treatment (Table 6). However, the limited number of these patients did not allow statistical analysis.
Beneficial effect of late recanalization: potential mechanisms.
The "open-artery" hypothesis is based on the observation that those hearts in which experimental coronary ligation is released develop less ventricular dilation than those in whose occlusion is maintained (15). Indeed, because LV dilation after myocardial infarction can be caused by lengthening of viable adjacent segments (16), a patent IRA may limit remodeling by enabling earlier formation of a firmer myocardial scar (17). Avoidance of unfavorable LV morphology results in many secondary, later benefits, such as a reduction of wall stress, prevention of volume overload, hypertrophy and improvement of ejection fraction. Indeed, in our study, even though patients revascularized after 4 h did not show any significant myocardial salvage, they also did not exhibit a trend toward progressive deterioration of LV function, as this is usually observed in post-infarction patients in whom the IRA remains occluded (18,19). Our results are in keeping with those of a recent study addressing the influence of an additional treatment delay inherent in the transfer of patients with AMI, who where first admitted to hospitals without invasive facilities, to a tertiary-care referral center for primary PTCA (20). In that study, the additional delay (albeit, all patients were reperfused within 6 h) had a deleterious effect on myocardial salvage, as reflected by a larger infarct size and a lower ejection fraction; however, the six-month clinical outcome was not affected.
Clinical implications.
The traditional paradigm in reperfusion therapy is that early reperfusion results in myocardial salvage and improved survival. The term "early" is not well defined. Previous studies have suggested that a significant amount of myocardium can be salvaged if recanalization is achieved within 2 h (1,10,21–23). In the present study, we found that myocardial salvage could also be achieved in patients reperfused within 4 h with primary PTCA. Indeed, in the majority of patients with AMI undergoing primary PTCA, reperfusion is effectively achieved within this time lag. It is important to note that in our patients, late PTCA (>4 h) was not associated with LV remodeling. Because these data support the open-IRA hypothesis, our proposal is to increase the window period for effective reperfusion to 4 h. An open IRA, even if too late for myocardial salvage, may prevent ventricular dilation and promote electrical stability, resulting in survival benefit (11,15–20,24).
A second implication of this study relates to the time course of LV function recovery after early reperfusion: immediate or in-hospital improvements of LV function are not to be expected, because significant changes occur only 30 days after reperfusion. This is probably related to myocardial stunning (25,26). In a previous study, we were able to demonstrate the efficacy of calcium antagonists against post-ischemic stunning in patients with AMI (27). Early recovery of LV function in patients with ischemic LV dysfunction can reduce 30-day mortality and cardiac events.
Another implication of this study relates to the significance of peak creatine kinase (CK) and CK-MB levels as reliable markers for infarct size. In the present study, the peak level of cardiac enzymes was not a predictor of infarct size and LV damage. Rather, the time to peak level correlated with the time to reperfusion, with early peaking occurring in patients who were reperfused early (<4 h). Early peaking of CK results from the abrupt washout of the previously occluded artery and its related vasculature (28–30). Improvement of LV function was independent of the total amount of CK released after reperfusion.
Finally, late restenosis in patients undergoing primary PTCA does not influence recovery of LV function at long-term follow-up, as long as TIMI flow grade 3 is preserved in the IRA. Consequently, the flow grade in the IRA, rather than restenosis, seems to be a better predictor of LV function recovery and survival benefit after primary PTCA.
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Abstract
Methods