Abstract

Background: Limited data is available about stroke developing after acute myocardial infarction (AMI). We investigated the incidence, risk factors and in-hospital outcome of stroke after AMI in clinical practice with and without use of thrombolysis.
Methods and results: We analyzed data from a prospective registry of consecutive patients admitted to the coronary care unit (CCU) at Mubarak Al Kabeer Hospital in Kuwait. Of 2481 patients admitted with AMI between1999 and 2003, 29 (1.2%) developed stroke during their hospital stay. Age older than 60 years (OR 5.5; 95% CI 2.4 to 12.5; P < 0.001) and systolic blood pressure higher than 160 mmHg (OR 3.2; 95% CI 1.1to 9.5; P < 0.04), were identified as independent predictors for stroke among patients with AMI. Patients who received thrombolytic therapy were not at an increased risk for developing stroke (OR 0.7; 95% CI 0.2 to 2.0). Patients developing stroke were 12 times more likely to die during hospitalization compared with patients who did not develop stroke (OR 12.6; 95% CI 5.4 to 26.7; P < 0.001).
Conclusions: Stroke is an infrequent but serious complication of AMI. Older age and high systolic blood pressure at admission are independent predictors of stroke. Heart Views 2007;8(4):142-146.
© Gulf Heart Association 2007.
Key Words: ¨ stroke ¨ acute myocardial infarction ¨ risk factors ¨ prognosis

 

Introduction

Stroke is an uncommon but serious complication of acute myocardial infarction (AMI) .The incidence and type of stroke has changed with the routine use of thrombolytic therapy for AMI. In the pre-thrombolytic era stroke occurred in 1.7-3.2% after AMI, and almost all strokes were thromboembolic1. In the Thrombolytic era the incidence of stroke has decreased to about 1.2%, and intracerebral hemorrhage became a frequent type of stroke2. Furthermore, some of the usual risk factors for stroke, such as anterior location of AMI, have recently been disputed3,4. In this study we aim to determine the incidence, risk factors and inhospital outcome of stroke after AMI in our clinical practice.

Methods

We analyzed data from a prospective registry of unselected patients consecutively admitted to the coronary care unit (CCU) of Mubarak-Al-Kabeer Hospital in Kuwait between 1999 and 2003. All patients admitted to the CCU during this period were registered and followed up during their hospital stay. Using a structured data collection form. This form included information on patients’ demographics, past medical history, risk factors, physical examination, ECG at presentation, cardiac enzymes, lipid profile, blood sugar, admission and discharge diagnosis, thrombolytic therapy administration, and inhospital course and outcome.
The diagnosis of AMI was based on the following criteria: Ischemic type of chest pain, diagnostic serial ECG changes, and elevation of creatine kinase (twice or more the normal value with at least 3% MB fraction) or Troponin-I.
Stroke was defined as the presence of a new neurological deficit that persisted for longer than 24 hours. The diagnosis was confirmed and the stroke type identified by a CT scan in all but one of the patients with the clinical diagnosis of stroke.

Statistical analysis

Categorical variables were compared using chi-square test. When the assumptions related to use of chi-square test was violated Fisher’s exact test replaced the chi-square test. Normal continuous variables between stroke and non-stroke groups were compared using t-test.

Results

During the study period, 2481 consecutive patients with AMI were identified. Of these, 29 patients (1.2%) developed stroke during their hospital stay. More than half of these strokes (62%) were hemorrhagic. There was no significant difference in stroke rates between patients who received thrombolytic therapy and patients who did not (1.2% vs 1.8% respectively). Table 1 shows the characteristics of patients with AMI according to the development of stroke. Patients who developed a stroke following AMI were significantly older and more likely to be smokers. These patients were also more likely to have a history of hypertension and to have a systolic blood pressure higher than 160 mmHg at presentation.
In a logistic regression model including 11 variables, risk factors for stroke were analyzed (Table 2). Age > 60 years was the strongest predictor of stroke after AMI among the variables we studied (OR 5.8; 95%CI 2.6 to 13.1; P < 0.001). Other predictors of stroke were systolic blood pressure at presentation higher than 160 mmHg (OR 4.2;95% CI 1.4 to 12.4; P < 0.01) and a past medical history of hypertension (OR 2.2; 95% CI 1.1 to 4.6; P < 0.05). Female gender and diabetes mellitus were not associated with a higher risk of stroke. Anterior location of AMI was also not associated with a higher risk of stroke (OR 1.4; 95% CI 0.7 to 3.0). Patients who received thrombolytic therapy were not at an increased risk for developing stroke (OR 0.7; 95% CI 0.2 to 2.0).
Using multivariate adjusted logistic regression two factors were identified as independent predictors for stroke among patients with AMI: age > 60 (OR 5.5; 95% CI 2.4 to 12.5; P < 0.001) and systolic blood pressure higher than 160 mmHg at presentation (OR 3.2; 95% CI 1.1to 9.5; P < 0.04) (Table 3).

As would be expected, outcomes in patients who developed stroke after AMI were worse than in those who did not develop stroke (Table 4). Patients developing stroke were 12 times more likely to die during hospitalization compared with patients who did not develop stroke (OR 12.6; 95% CI 5.4 to 26.7; P < 0.001). Patients who developed stroke after receiving thrombolytic therapy had a higher mortality than patients developing stroke without receiving this treatment (47% vs 0%). Among patients who survived after stroke, the length of hospital stay was significantly longer than it was for patients who did not develop stroke (HR 4.9; 95% CI 2.1 to 8.6; P < 0.001).

Study limitations

The case report form used in our registry did not include information on known risk factors for stroke such as chronic atrial fibrillation, previous history of stroke or transient ischemic attacks. Accordingly, these variables could not be considered in the analysis.

Discussion

The incidence of stroke after AMI in our study was 1.2% which is comparable to that reported from National Registry of Myocardial Infarction-2 (NRMI-2) and from Maximal Individual Therapy in Acute Myocardial Infarction Trial (MIR/MITRA)5,6. Our results support a decline in the incidence and event rate of ischemic stroke after AMI. In the 1970s and 1980s the risk of stroke after AMI was high at a rate of 2.3 to 3.8% in studies examining the effect of warfarin in AMI and at a rate of 0.9 to 1.9% in observational studies from coronary care units7,8,9. In the 1990s, the stroke event rate was lower at a rate of 0.8 to 1.1% in the placebo groups of large thrombolysis trials10,11,12. In a recently conducted registry of acute coronary syndromes in Kuwait, the incidence of stroke was 0.3% among Patients with AMI13.
The decrease in the incidence of post AMI ischemic stroke in recent decades is possibly explained by early mobilization of patients with AMI and the routine use of thromblytics and aspirin. The use of aspirin has resulted in impressive reduction (42%) of post AMI stroke in a large randomized study11. Our finding that thrombolytic therapy is not associated with an increased risk of developing stroke is in agreement with results from the 3 largest placebo – controlled trials of thrombolytic treatment after AMI11,12,14.
Our results show that older age and hypertension are associated with a higher event rate of stroke, This is in agreement with findings from Behar S et al15. Advanced age is consistently shown to be a strong predictor of stroke following AMI in clinical trials and registries. Patients aged 65-75 and patients aged over 75 were respectively 2.1 and 2.42 times more likely to have a stroke after AMI than those under 65 years12. Severe AMI complicated by reduced cardiac output and poor cerebral perfusion predisposes to the development of stroke especially in elderly patients usually having subcritical cerebrovascular stenosis16.
Hypertension is the most powerful, prevalent and treatable risk factor for stroke17. Both systolic and diastolic blood pressures are independently related to stroke incidence. Isolated systolic hypertension which is common in the elderly consistently increases the risk of stroke by 2 to 4 times. The importance of on anterior location of infarction and left ventricular thrombus as risk factors for stroke has recently been disputed3,4. We did not find that anterior location of the infarction to be an important predictor of stroke, this is in accordance with previous studies12,15. Embolization from a left ventricular thrombus can explain only a small fraction of AMI- related strokes. Haemodynamic changes, cerebral vessels atherosclerosis, the inflammatory response to infarction and hemostatic abnormalities18, may be other factors predisposing to ischemic stroke.
In conclusion, stroke is an infrequent but serious complication of AMI, older age and high systolic blood pressure at admission are independent predictors of stroke. Patients who received thrombolytic therapy are not at increased risk for developing stroke.¨

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