Intermittent BBB and Supraventricular Aberrancy

If one of the bundle branches repolarizes slightly slower than the other, it would be possible to find a heart rate that would be slow enough to allow one bundle branch adequate time for repolarization, but too fast to allow the other bundle branch adequate time for repolarization. Such a circumstance produces what is called a rate dependent BBB. As soon as the R-to-R intervals become shorter than the time required for the repolarization of the slower of the two bundle branches, the patient's...

Hyperkalemia

Hyperkalemia Ecg

Many of the ECG changes seen with hyperkalemia are simply the opposite of those seen with hypokalemia. As serum potassium levels begin to rise above approximately 5.5 mEq L, T waves become very tall and peaked (Figure 13.2). J-point ST elevation may occur, simulating AMI. Further elevations in Figure 13.2. ECG changes associated with moderate hyperkalemia. Note that T waves are tall and symmetrically peaked, and that there is mild J point elevation in V2 and V3. Figure 13.2. ECG changes...

Other Pitfalls to Diagnosing AMI Ventricular Aneurysm

Earlier in this chapter, it was mentioned that observing the evolution of AMI on serial ECG tracings leads to a more accurate diagnosis than does reading a single tracing. One of the reasons why this is true is that, occasionally, I II III aVRaVLaVF V1 V2 V3 V4V5V6 Figure 9.17. Ventricular aneurysm. Persistent ST elevation 4 years after acute anterior wall infarction in a 75-year-old male with aneurysm of the left ventricle proven by echocardiogram. Note the absence of reciprocal depression as...

Q Waves as Scars

It was mentioned earlier in the chapter that the ST elevation and T wave inversion seen in STEMI frequently resolve over time, but that the Q wave may persist indefinitely as evidence of a past infarction. Pathologic Q waves in the absence of AMI are therefore sometimes referred to in ECG reports as scars or remote infarctions. Figures 9.10 and 9.11 show remote inferior and anterior infarctions, respectively, in which the ST elevation and T wave inversion have resolved but Q waves persist as...

Syndromes of Ischemic Heart Disease

Zones Infarct

The continuum of ischemic heart disease stretches from silent ischemia through the various patterns of angina, AMI, and scars of a previous myocardial infarction, to the complications of AMI, such as ventricular aneurysm or pericarditis. Although all of these syndromes represent a continuum of the same disease process, they may present with quite different ECG patterns at different stages of the continuum, and have distinctly different treatments and outcomes. When a patient presents with chest...

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

Pathological

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...

Answers and Case Discussion

This late middle-aged black male presents with a history of stable angina under current treatment with calcium channel blockers, beta blockers, and prn nitroglycerin. His pain usually comes with exertion, but today it came at rest and has continued for 30 min through to the time of admission. Although he has had no nausea, vomiting, diaphoresis, or shortness of breath, his pain almost certainly represents heart pain, and his symptoms are certainly compatible with AMI. We are not surprised that...

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...