ST elevation myocardial infarction triggers

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Following the sudden death of Tim Russert of NBC's Meet the Press on June 13th 2008, many laypeople and physicians alike have asked "what are the triggers of a sudden heart attack"? Barbara Walters speculated that Tim Russert may have died from "the stress of the job". Others were concerned about a recent weight gain and lack of sleep. This chapter reviews the literature pertaining to triggers of acute MI.

Overview
Several factors have been associated with an increased risk of developing ST elevation myocardial infarction (STEMI). These factors include physical exertion, psychological stress, sexual activity, diurnal (daily) variations in cortisol and platelet aggregation and circannual (yearly) variations in lipids and infectious etiologies, exposure to pollution and or particulate matter, cocaine and ingestion of a recent fatty meal.

Nomenclature
Muller et al have developed the following nomenclature to categorize and analyze data pertaining to triggers of MI :


 * (1) Trigger: An activity that produces short-term physiological changes that may lead directly to onset of acute CVD.


 * (2) Acute risk factor: A short-term physiological change, such as a surge in arterial pressure or heart rate, an increase in coagulability, or vasoconstriction, that follows a trigger and may result in disease onset.


 * (3) Hazard period: The time interval after trigger initiation associated with an increased risk of disease onset because of the trigger. The onset and offset times of the hazard period, which could also be designated a “vulnerable period,” may be sharply defined, as in heavy exertion, or less well defined, as with respiratory infection. The duration of the hazard period may also vary, eg from < 1 hour during heavy physical exertion to weeks or months with bereavement.


 * (4) Triggered acute risk prevention (TARP): Cardiovascular risk reduction that focuses on the short-term increase in risk associated with a trigger.

Putting Relative Risk of MI and Absolute Risk of MI Into Clinical Context
In the following sections, you will read that certain triggers are associated with a dramatic rise in the relative risk of having an MI (e.g. heavy exertion among patients with a sedentary lifestyle increases their risk of an MI 107 fold). These dramatic increases in relative risk, must, however, be placed in the appropriate clinical context.

It must be born in mind that while triggers are frequent events, MI or sudden death are relatively infrequent events. The risk of sudden death with exercise provides a nice example. The relative risk of sudden death within 30 minutes after >/= 6 METS of exercise goes up 16.9 fold. However, because sudden death is so infrequent, this translates into 1 sudden cardiac death for every 1.51 million episodes of heavy exertion. The number of absolute events is even lower among nurses in the Nurses Health Study undertaking mild to meoderate exertion: 1 sudden death for every 36.5 hours of exertion.

"While the presence of triggers increases the relative risk of MI dramatically, the absolute number of MIs attributable to the trigger may be quite low."

A dramatic rise in the relative risk of a very, very, very infrequent event therefore translates clinically into a very small rise in the absolute number of events attributable to the trigger.

Differential Diagnosis of Underlying Causes and Triggers of ST Segment Elevation in the Presence of Myonecrosis (STEMI)
While plaque rupture is the most common cause of ST segment elevation MI, other conditions can cause ST elevation and myocardial necrosis. In order to expeditiously treat an alternate underlying cause of myonecrosis, it is important to rpadily identify conditions other than plaque rupture that may also cause ST elevation and myonecrosis. Indeed, the management of some of these conditions might be differ substantially from that of plaque rupture: cocaine induced STEMI would not be treated with beta-blockers, and myocardial contusion would not be treated with an antithrombin. These conditions include the following:

Physical Exertion and MI
Physical exertion, especially if the exertion is much more intense than the individual usually performs has been associated with the onset of STEMI. The ONSET study demonstrated that intense exertion (defined as >/= 6 metabloic equivalents of METS) within the previous hour was associated with a 5.9 fold rise in the risk of MI.

Studies Linking Physical Exertion to MI
 * The ONSET Study: Relative risk = 5.9
 * The Stockholm Heart Epidemiology Program (SHEEP): Relative risk = 6.1
 * The Triggers and Mechanisms of Myocardial Infarction (TRIMM) study: Relative risk = 2.1

Blizzards have often been cited as a trigger of MI, and the physical exertion of snow shoveling has frequently been cited as a contributor.

Impact of a Sedentary Lifestyle

The relative risk of MI quoted above increases dramatically among those individuals who lead a sedentary lifestyle. For those in poor physical condition, the relative risk was 107 fold higher in the ONSET study. In contrast, among those individuals who reported that they engaged in physical activity 5 days a week or more, the risk was only doubled.

Mechanism

It has been hypothesized that exertion increases blood pressure, pulse and oscillatory shear which in turn may increase the risk of plaque rupture.

Physical Exertion and Sudden Death
While the above discussion pertains to documented nonfatal MI, approximately a quarter of MI patients may die of sudden death or fatal MI before reaching the hospital. In a cohort of 21,481 male physicians in the United States who by self report who had no prior history of coronary artery disease, there was a 16.9 fold rise in the risk of sudden cardiac death within 30 minutes of intense exertion (>/= 6 METS). Similar to what has been reported with respect to the onset of MI, there was no increase in the risk of sudden death with heavy exertion among those nurses who exercised more than 2 hours per week.

Psychological Stress
Psychological stress associated with anger, work related stressful events , wartime bombing , earthquakes and other natural disasters has been associated with an increased risk of onset of myocardial infarction.

Anger
Intense anger (fist / teeth clenched) has been associated with a risk in the risk of MI in the 2 hours following the episode in the following studies:

ONSET: 2.3 fold rise

SHEEP: 9 fold rise

Kotton et al: 14 fold rise

The psychosocial stressors that precipitated the anger were as follows:


 * 1) Argument with family members (25%)
 * 2) Conflicts at work (22%)
 * 3) Legal problems (8%)

Anxiety
If a patient is in the >75th percentile for anxiety, this increases the relative risk of MI 1.6 fold for the 2 hours following the period of anxiety.

Bereavement and the Broken Heart Syndrome
Stress cardiomyopathy which is also known as Left Ventricular Apical Ballooning Syndrome, Takotsubo cardiomyopathy, or Ampulla-Shaped Cardiomyopathy is a cardiac syndrome characterized by a reversible transient apical ventricular dysfunction. Since the cardiomyopathy is often triggered by emotional stress, such as the death of a loved one, the condition is sometimes also referred to as the Broken Heart Syndrome. In 2006, the syndrome was renamed Stress Cardiomyopathy, and was classified as an acquired cardiomyopathy.

The typical presentation of someone with takotsubo cardiomyopathy is a sudden onset of congestive heart failure or chest pain associated with EKG changes suggestive of an anterior wall acute MI. During the course of evaluation of the patient, a bulging out of the left ventricular apex with a hypercontractile base of the left ventricle is often noted. It is the hallmark bulging out of the apex of the heart with preserved function of the base that earned the syndrome its name "tako tsubo", or octopus trap in Japan, where it was first described. Evaluation of individuals with takotsubo cardiomyopathy typically include a coronary angiogram, which does not reveal any significant blockages that would cause the left ventricular dysfunction. Provided that the individual survives their initial presentation, the left ventricular function improves within days to weeks. Takotsubo cardiomyopathy is more commonly seen in post-menopausal women. Often there is a history of a recent severe emotional or physical stress.

Deadlines
An agressive timeline or deadline at work has been associated with a rise in the risk of MI:

The SHEEP study: 6 fold rise

The ONSET study: 2.3 fold rise

Firing an Employee
The stress of firing an employee has been associated with a rise in the risk of MI:

The ONSET study: 2.2 fold rise

Natural Disasters
Natural disasters have been associated with an increased risk of MI. The best documented association has been with earthquakes. For instance the 1994 earthquake in Los Angeles was associated with a 4 fold rise in the risk of sudden death and a 35% rise in the relative risk of a non-fatal MI. It is notable that the association of earthquakes with MI is variable depending upon the time of day that the earthquake occurs. The LA eathquake occurred just after 4 A.M., just when platelet aggregation may be at a peak (see below). However, the earthquake that struck San Francisco Bay in 1989 at 5 P.M. was not associated with an increased risk of MI.

9/11/2001
Within 50 miles of the world trade center, there was a 49% increase in the relative risk of an MI in the 60 days following the 9/11 attack: There were 118 MIs in the 60 days after the attack versus 79 MIs in the 60 days before (p=0.01). How much of this is attributable to particulate matter versus psychological stress is not clear.

Missile Attacks
The stress of missile attacks has been associated with a doubling in the risk of non fatal MI and sudden death.

Sporting Events
The stress of sporting events has been associated with an increased risk of MI in a population. An example that has been cited is the 50% increase in the risk of MI or stroke among Dutch men associated with the loss of Holland to France in the 1996 European football finals. It is notable that no such rise in risk was observed among Dutch women or the French.

Sexual Activity
The association of sexual activity with the onset of MI may represent components of physical exertion as well as psychologic stress. In both the SHEEP and the ONSET studies, recent sexual activity increased the risk of MI by 2.5 fold. Again, to place this relative risk into clinical context, it should be noted that only 3% of MI patients had had sexual intercourse within the past 2 hours prior to the onset of MI. It should also be noted that the increase in risk of MI with sexual activity did not differ between patients with and without a history of coronary artery disease.

The risk of MI with sexual intercourse is a frequent concern among patients who have coronary artery disease. Again, the data above indicates that recent sexual activity doubles the risk of an MI, and this may on the surface appear to be disconcerting to both a patient and healthcare professional. But again, to place this relative risk into context, the absolute risk must be taken into account. The average risk of an MI in a patient at average risk has been estimated to be about 1 chance in a million during any given hour during middle age. Sexual activity increases that risk to 2 in a million per hour for the 2 hours after sexual intercourse. If the annual risk of MI is about 1%, weekly sexual intercourse will increase this annual risk to just 1.01%. As is the case with physical exertion, regular exercise (6 METS >/= 3 times per week) reduced the relative risk of MI with sexual intercourse from 3.0 to 1.2 in the ONSET study.

Thus, because the risk is small, because the frequency of sexual activity is relatively small, and because the period of increased risk is short (approximately 2 hours) the absolute risk of MI associated with sexual intercourse is quite small.

Air Pollution / Fine Particulate Matter
Exposure to high levels of ambeint air pollution (exposure to fine particulate matter in the past 2 - 24 hours) has been associated with a transient elevation in the risk of myocardial infarction. There is a rise in CRP and plasma viscosity following exposure to fine particulate matter and it has been speculated that the pulmonary inflammation that follows such exposure may trigger a systemic state of hypercoagulability. Exposure to fine particulate matter has also been associated with changes in autonomic tone manifested by sinus tachycardia, as well as a reduction in heart rate variability. Finally, ventricular arrhythmias as manifested by firing of AICDs has been associated with exposure to fine particulate matter.

Antecedent Infection
Acute severe infection, such as pneumonia, can trigger myocardial infarction. A more controversial link is that between Chlamydophila pneumoniae infection and atherosclerosis. While this intracellular organism has been demonstrated in atherosclerotic plaques, evidence is inconclusive as to whether it can be considered a causative factor. Treatment with antibiotics in patients with proven atherosclerosis has not demonstrated a decreased risk of heart attacks or other coronary vascular diseases.

A Heavy Meal
There have been reports of a 4 fold rise in the risk of MI following a heavy meal.

This rise in risk may account for a second peak in the circadian variation in the onset of MI around 8 P.M. in the evening. The mechanism underlying the association is not clear. It has been speculated that ingestion of a heavy fatty meal may be associated with a rise in prothrombotic factors and heart rate, and a reduction in vascular reactivity.

Cocaine
Ingestion of cocaine has been associated with STEMI.

Marijuana
Marijuana use has been associated with a 4.8 fold rise in the risk of MI.

Circadian Variation in Onset of STEMI
Most MIs occur in the early morning hours when cortisol and adrenaline rise and platelets are more activated. This diurnal variation is obliterated with aspirin therapy, pointing to the putative role of platelets in the initiation of MI.

Relative Frequency of Triggers in Association with MI
When a creful history is obtained, approximately half (48%) of MI patients will report a trigger . It is notable that 13% of patients will report that there were of 2 or more triggers. The following triggers were most commonly associated with the onset of MI in the Multicenter Investigation of Limitation of Infarct Size (MILIS) study .:


 * 1) Emotional upset (18%)
 * 2) Moderate physical activity (14%)
 * 3) Heavy physical activity (9%)
 * 4) Lack of sleep (8%)
 * 5) Overeating (7%)