B P5 C37 ST-Elevation Myocardial Infarction: Pathophysiology and Clinical Evolution Flashcards
Type of MI
Demonstration of acute atherothrombosis in the artery supplying the infarcted myocardium
Type 1
Acute myocardial infarction should be used when there is acute myocardial injury with clinical evidence of acute myocardial ischemia and with detection of a rise and/or fall of cTn values with at least one value above the 99th percentile URL and at least one of the following:
• Symptoms of myocardial ischemia
• New ischemic ECG changes
• Development of pathologic Q waves
• Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality in a pattern consistent with an ischemic etiology
• Identification of a coronary thrombus by angiography or autopsy (not for type 2 or 3 MIs)
An imbalance between myocardial oxygen supply and demand unrelated to acute atherothrombosis meets criteria for _________
Type 2 MI
Cardiac death in patients with symptoms suggestive of myocardial ischemia and presumed new ischemic ECG changes before cTn values become available or abnormal meets criteria for ____________
Type 3 MI
Percutaneous coronary intervention (PCI)-related MI is termed _______________
Type 4a MI
Type 4b MI ______________
Type 4c MI ______________
Type 4 MI include type 4b MI stent thrombosis and type 4c MI restenosis that both meet type 1 MI criteria.
Coronary artery bypass grafting (CABG) related MI is termed _______________
Type 5 MI
Coronary procedure related MI </= 48 hr after the index procedure is arbitrarily defined by an elevation of cTn values > ___ times for type 4a MI and >___ for type 5 MI of the 99th percentile URL in patients with normal baseline values.
> 5x: type 4a
> 10x: type 5
Patients with preprocedural cTn values, in whom the preprocedural cTn level is stable (<20% variation) or falling, must meet the criteria for a >5 or >10 fold increase and manifest a change from the baseline value of >_____%.
> 20%
Criteria for prior or silent /unrecognized MI
- Abnormal Q waves +/- symptoms in the absence of nonischemic causes.
- Imaging evidence of loss of viable myocardium in a pattern consistent with ischemic etiology.
- Pathoanatomical findings of a prior MI.
Management and outcomes of patients with STEMI appear to vary substantially depending on the volume of such patients cared for within a hospital system.
_____ have lower STEMI mortality rates.
Conversely, patients with STEMI _____ have higher mortality rate
LOWER STEMI Mortality:
Hospitals with a high clinical volume
High rate of invasive procedures
Top ranking in quality reports
HIGHER MORTALITY RATE:
Not cared for by a cardiovascular specialist
The highest risk of ischemic complications following MI occurs within ____ days, after which the risk becomes fairly linear. This pattern is most evident in patients older than 80 years
180 days
Identify type of MI:
Any one of the following criteria meets the diagnosis for prior or silent/ unrecognized MI:
• Abnormal Q waves with or without symptoms in the absence of nonischemic causes.
• Imaging evidence of loss of viable myocardium in a pattern consistent with ischemic etiology.
• Pathoanatomical findings of a prior MI.
Prior or silent/unrecognized myocardial infarction
Cause of myocardial injury related to AMI
Atherosclerotic plaque disruption with thrombosis
Most ACSs result from coronary atherosclerosis, generally with superimposed coronary thrombosis caused by_____
Rupture or erosion of an atherosclerotic lesion
Thus, equating the lipid-rich, thin-capped plaque with “vulnerability” is a misnomer. Other morphologic characteristics associated with rupture-prone plaque include _____.
Expansive remodeling that minimizes luminal obstruction (mild stenosis by angiography)
Neovascularization (angiogenesis)
Plaque hemorrhage
Adventitial inflammation
“Spotty” pattern of calcification
Infarction alters the sequence of depolarization ultimately reflected as changes in the QRS-T complex.
The most characteristic change in QRS that develops in most patients with STEMI is the evolution of _____ in leads that interrogate the infarct zone.
Q waves
In a minority of patients with ST elevation, no Q waves develop but other abnormalities in the QRS complex occur frequently, such as diminution in R wave height and notching or splintering of the QRS
Myocardial injury related to acute myocardial ischemia because of oxygen supply/demand imbalance
Identify causes with reduced myocardial perfusion
• Coronary artery spasm, microvascular dysfunction
• Coronary embolism
• Coronary artery dissection
• Sustained bradyarrhythmia
• Hypotension or shock
• Respiratory failure
• Severe anemia
Causes of Increased myocardial oxygen demand
Sustained tachyarrhythmia
Severe hypertension with or without left ventricular hypertrophy
Gross alterations in the myocardium appear _____ hours after the onset of necrosis, but a variety of histochemical stains can identify zones of necrosis after only _____ hours.
6-12 hours: Gross alterations
2-3 hours: Histochemical stains
Within hours of death from MI, the presence of an infarct can often be detected by immersing slices of myocardium in triphenyltetrazolium chloride (TTC), which turns noninfarcted myocardium a _____ color due to preserved lactate dehydrogenase activity while the infarcted area _____
Birck-red color: NONINFARCTED
Unstained: INFARCTED
An MI can often be identified at _____ hours as a red-blue area of disco-oration caused by edema and extravasated blood.
By day ____, an infarct is rimmed by a zone of granulation tissue as it eventually evolves into a fibrous scar.
12-24 hours: RED-BLUE AREA
DAY 7
Approximate time of onsent of key events in ischemic cardiac myocytes
Onset of ATP depletion:
Loss of contractility:
ATP reduced
to 50% of normal:
to 10% of normal:
Irreversible cell injury:
Microvascular injury:
Onset of ATP depletion: Seconds
Loss of contractility: <2 min
ATP reduced
to 50% of normal: 10 min
to 10% of normal: 40 min
Irreversible cell injury: 20–40 min
Microvascular injury: > 1 hr
Myocardial relaxation-contraction is compromised within a minute after the onset of severe ischemia with loss of systolic function, and irreversible cell injury begins within as early as _____________
20 minutes
Irreversible cell death usually occurs in the ischemic region in _____ hrs in the absence of reperfusion or sufficient collateral circulation
6 hours