Medical management following myocardial infarction
Besides supplemental oxygen for at least six hours post MI and bed rest, and continuous electrocardiography monitoring for at least 12 hours post-MI, consider the role of primary percutaneous revascularization and intra-aortic balloon pump support for some patients.
Cardiac catheterization provides an effective way to check blood flow in the coronary arteries. Consider early cardiac catheterization during hospitalization for patients with recurrent symptoms, serious complications, or other serious high-risk features (i.e. hypotension, congestive heart failure, recurrent chest pain).
Numerous studies support the use of cardiac catheterization to aid post-MI recovery.
Consider prompt transfer to a referral center for primary percutaneous coronary intervention (PCI) as an alternative to thrombolytic therapy in experienced centers, particularly in patients with ST-segment elevation, new LBBB, or true posterior acute MI. PCI is associated with a lower 30-day mortality rate and lower risk of hemorrhagic stroke compared with thrombolytic therapy. Note that the beneficial effects of transfer for PCI are contingent upon transfer within two to three hours of initial hospital arrival.
If any coronary arteries are blocked, PCI using a catheter, guide wire, and balloon opens them and improves blood flow. The three most common types of PCI are:
- Angioplasty - uses balloons to widen and increase blood flow in blocked arteries, resulting in decreased angina and heart attack risk and increased ability for physical activity.
- Stenting - a wire tube often inserted during angioplasty to hold open the artery improve blood flow. Reclosure of the artery is less likely when a stent is used.
- Atherectomy - similar to angioplasty, using a rotating, shaver-tipped catheter or laser beam to remove plaque and open the blocked artery.
The American Heart Association's practice guidelines advise that cardiac catheterization with subsequent percutaneous or surgical revascularization is appropriate in patients with recurrent ischemic-type chest discomfort. Numerous studies support the use of cardiac catheterization to aid post-MI recovery. For example, recent studies showed that an early invasive approach (i.e., cardiac catheterization within four to 48 hours after presentation) vs. a conservative approach in combination with a GP IIb/IIIa inhibitor in patients with non-ST-segment elevation MI or unstable angina significantly reduces major cardiac events.
Furthermore, consider placement of an intra-aortic balloon pump (IABP) during cardiac catheterization in specific subsets of patients, such as those with refractory post-MI angina, for stabilization before angioplasty and revascularization or cardiogenic shock. The IABP reduces afterload during systole and increases coronary perfusion during diastole. Studies have shown that in selected patient populations, IABP significantly improves survival rates.
See chart, "Risk Stratification and Management of Patients With Acute Coronary Syndrome," from PIER's module on acute coronary syndromes.
Exercise Stress Testing
Use exercise stress testing for prognostic assessment in stable patients post MI without high-risk features, such as hypotension, CHF, recurrent chest pain or inability to exercise. By doing stress testing early post-MI, the clinician can assess functional capacity, evaluate efficacy of the patient's current medical regimen, and risk stratify the patient according to likelihood of future cardiac events.
- Consider an exercise treadmill test with or without radionuclide imaging if the patient can exercise, and a pharmacologic stress test if the patient cannot exercise.
- Obtain a submaximal stress test four to seven days post MI or a symptom-limited exercise test at 14 to 21 days post-MI. A submaximal protocol has a predetermined endpoint of a heart rate of either 120 bpm, 70% of predicted maximum heart rate, or a peak MET level of 5. A symptom-limited test continues until the patient shows signs or symptoms that require the test to be terminated (i.e. angina, fatigue, ST-segment depression > 2 mm, ventricular arrhythmias, or > 10 mm Hg drop in systolic BP from baseline).
- Consider the addition of imaging (myocardial perfusion or echocardiography) to improve the sensitivity and specificity of the test.
Predictors of future adverse events in post-MI patients include inability to exercise, exercise induced ST-segment depression, failure to achieve five METs during treadmill testing, and failure to increase systolic blood pressure by 10 to 30 mm HG during exercise.
Note that the AHA guidelines recommend concomitant nuclear imaging when baseline abnormalities of the ECG limit interpretation, and there is some evidence that nuclear imaging can also aid in further risk stratification. In one study, stable post-MI patients underwent assessment of LV function and had adenosine tomography done early (5±3 days) after infarction. Cardiac events occurred in 30 (33%) of 92 patients over 15.7 ± 4.9 months. Independent predictors of all events were quantified perfusion defect size (P<0.0001), absolute extent of LV ischemia (P<0.000001) and ejection fraction (P<0.0001). The results suggested that risk stratification of individual patients early after infarction is possible based on the extent of ischemia and severity of LV dysfunction.
Strongly encourage patients to participate in a cardiac rehabilitation program to prevent recurrent heart attacks. Cardiac rehabilitation programs should include:
- Exercise training
- Strategies for reducing modifiable risk factors for cardiovascular disease, including managing lipid levels, diabetes, blood pressure and weight
- Nutritional and smoking cessation counseling
- Encouragement to adhere to prescribed drug therapy
- Psychosocial and vocational or occupational counseling
- Baseline and follow-up patient assessments
Exercise training alone can improve blood vessel function, cardiovascular risk factors, improved coronary blood flow, and electrical stability of the heart muscle while also reducing the risk of blood clots and cardiac work and oxygen requirements. Research has shown that average cardiac death was 26% lower in rehabilitation patients who were exercise-trained compared with those who received usual care, and there were also 21% fewer nonfatal heart attacks, 13% fewer bypass surgeries and 19% fewer angioplasties in the exercise-trained people, according to an updated scientific statement in 2005 from the American Heart Association.
Counsel all patients who smoke to quit. Studies have shown that smoking triggers coronary vasospasm, reduces the anti-ischemic effects of beta-blockers, and doubles the risk of death after MI. Consider referring patients to a smoking cessation program and prescribing nicotine replacement therapy. Combining pharmacotherapy with behavioral therapy increases cessation success rates.
A heart healthy diet is recommended to reduce LDL and blood pressure. Heart healthy diet guidelines include:
- limiting total calories from fat to < 30% or less of the day's total calories.
- limiting total calories from saturated fat to 8-10% of the day's total calories.
- limiting cholesterol intake to < 300 milligrams per day.
- limiting sodium intake to 2,400 milligrams a day.
- consuming just enough calories to achieve or maintain a healthy weight and reduce blood cholesterol level.
Among patients who drink alcohol, moderate consumption is advised. To assist with dietary changes, consider referring patients for consultation with a registered dietitian.
Provide patients with specific instruction on the type and level of activity that is permissible. Activity may be beneficial to patients' cardiovascular and emotional health.
- Encourage daily walking immediately after hospital discharge.
- Follow driving regulations depending on applicable state laws.
- Counsel that sexual activity can be resumed in stable patients within seven to 10 days.
- Individualize instructions regarding strenuous activity, such as heavy lifting, climbing stairs and yard work, to each patient based on results of exercise testing.
Note that no randomized clinical trials have assessed when to resume normal activity, however the ACC/AHA guidelines are in accordance with the above recommendations.
Talk with patients about the fact that heart attack patients feel a wide range of emotions including depression, fear, and anger, for about two to six months post-MI. The emotional aftermath of MI can be disruptive to returning to normal life, and may require counseling or other intervention. Consider screening for depression in all patients post-MI. Studies indicate that about 20% of patients experience depression after acute MI and that the presence of depression is associated with increased risk for recurrent hospitalization and death.
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