Pathogenesis of AMI

In the mid 1960s, most respected pathologists held the view that AMI was the result of fixed obstructive disease of the coronary arteries, and that clot formation rarely played a role in AMI. In fact, at that time the old term coronary thrombosis was dropped from the lexicon, and the familiar term myocardial infarction substituted in its place. Studies performed in the 1970s and 1980s, however, confirmed that an acute thrombosis occurring at the site of a ruptured atherosclerotic plaque...

The PR Interval

The PR interval corresponds to the time it takes an impulse to travel from the SA node all the way down through the conduction system to the first muscle fibers stimulated in the ventricles. Therefore, it is measured from the beginning of the P wave to the beginning of the QRS. Note that in Figure 2.1, although you can see depolarization of the atria in the form of the P wave, you cannot see the impulse traveling through the AV node, bundle of His, Figure 2.2. Two different kinds of P wave...

Q Wave Formation

When a transmural segment of myocardium undergoes infarction, it ceases to depolarize normally and becomes essentially electrically inert. As a result, there are no forces of ventricular depolarization spreading from endocardium to epicardium and coming directly toward whichever leads are viewing the infarcted wall. Instead, the leads viewing the infarction are looking through the window of inactive infarcted myocardium at the forces of the opposite wall of the ventricle. These vectors in the...

Confusion of LAH with Inferior Wall Myocardial Infarction

You will later learn that one of the hallmarks of AMI is the development of Q waves. In inferior wall myocardial infarction, very deep Q waves can develop in the leads that look at the inferior wall of the heart, that is, in leads II, III, and aVF (Figure 6.6). Figure 6.6. Old inferior wall myocardial infarction with Q waves in leads II, III, and aVF, and with an axis of approximately -5 degrees. Figure 6.6. Old inferior wall myocardial infarction with Q waves in leads II, III, and aVF, and...

Electrocardiographic Hallmarks of STEMI

Segment Types Ami

Figure 9.2 illustrates the following three ECG hallmarks of a classic STEMI These three changes in the ECG typically evolve over a period of minutes to hours, with ST elevation usually appearing first, followed variably by T wave inversion and Q wave formation. Subsequently, the changes may show slow resolution, usually over a period ranging from days to months. Q waves, however, may persist indefinitely, producing ECG evidence of a scar. Figure 9.2. The three ECG hallmarks of AMI, including ST...

Identifying Candidates for Thrombolysis

Potential Candidates for Thrombolytic Therapy Include 3. Duration of pain < 12 hours 5. No absolute contraindications. It is not necessary or even desirable to confirm STEMI with enzyme (biochemical marker) determinations. Indeed, reliance on laboratory testing for confirmation of diagnosis is one of the causes of unnecessary delays in administration of therapy. ECG criteria for compatibility with STEMI should include ST elevation of 1 mm or greater in at least two contiguous (adjacent) limb...

Case

You are functioning as an emergency department physician. It is 10 15 PM. The nurses ask you to see a 52-year-old white female with a chief complaint of epigastric and lower retrosternal indigestion that radiates through to between her shoulder blades. The pain came on at approximately 6 45 PM, shortly after a supper of ham and potatoes. She has never had a similar pain. She admits to nausea, and she vomited one time shortly after dinner. Her blouse became damp with perspiration after vomiting....

The QRS

The QRS is naturally the largest complex on the ECG because it corresponds to depolarization of the ventricles, with their larger muscle mass. Therefore, QRS amplitude may normally reach as high as 25 mm or more five big boxes in large individuals, or in those with thin chest walls that actually allow the precordial electrodes to be closer to the heart. Amplitudes gt 25 mm are frequently associated with chamber enlargement ventricular hypertrophy , as seen in Figure 2.5. Conversely, very low...