Ii

FIGURE 6 An ECG from a patient with left ventricular hypertrophy. The mean electrical axis is approximately —60°. Note that P waves are absent in this trace because the heart was responding to a pacemaker near the bundle of His.

Myocardial Ischemia Produces a Current of Injury

aVR

FIGURE 7 An ECG from a patient with left bundle branch block. The mean electrical axis is approximately —30°, a left axis deviation. Note the long duration of the QRS complex, reflecting the delayed conduction to the left ventricle. This patient also was in atrial fibrillation, as indicated by the rhythm strip below.

FIGURE 7 An ECG from a patient with left bundle branch block. The mean electrical axis is approximately —30°, a left axis deviation. Note the long duration of the QRS complex, reflecting the delayed conduction to the left ventricle. This patient also was in atrial fibrillation, as indicated by the rhythm strip below.

heart), the electrical axis tends to have the same orientation. As shown in Fig. 5, the normal range for the mean electrical axis is from 0° to +90°. Certain pathologic conditions can cause a change in this axis. For example, if the left ventricle were to become hypertrophied (enlarged), then the mass of tissue would be increased on the left side of the heart. This could cause the dipoles generated from activation of the left ventricle to be much greater in magnitude than those from the right ventricle. Left ventricular hypertrophy might therefore shift the mean electrical axis to the left. When the shift is sufficient to move the mean electrical axis out of the normal range, it is called a left axis deviation. Thus, a mean electrical axis of —45° should alert the physician that left ventricular hypertrophy may be present. That diagnosis, of course, would have to be confirmed by additional tests such as an echocardiogram. Figure 6 shows an ECG from a patient with left ventricular hypertrophy. Hypertrophy of the right ventricle can cause a right axis deviation and thus an electrical axis between +90° and + 180°.

An axis deviation is commonly caused by failure of one of the bundle branches to conduct. If the left bundle is blocked, then conduction over the left ventricle will be slower than normal because the fast Purkinje fibers will not be used for conduction. The slowed activation will abnormally prolong the duration of the QRS. The electrical axis will also be shifted to the left because the wave of depolarization will continue on the left ventricle long after it has been completed on the right ventricle. Figure 7 shows an ECG from a patient with a left bundle branch block. The distinguishing feature between Figs. 6 and 7 is that the QRS interval in Fig. 6 is about 0.08 sec, whereas that in Fig. 7 is about 0.16 sec. Similarly, an abnormally prolonged QRS duration and a right axis deviation would characterize a right bundle branch block. Such blocks may occur as a congenital defect and be of little consequence. If a bundle branch block were instead to be acquired, as was the case in the patient in Fig. 7, it would indicate the electrical conduction tissue was being interrupted by either progressive fibrosis as is seen in advanced age or by necrosis as seen in myocardial infarction.

Get Rid of Gallstones Naturally

Get Rid of Gallstones Naturally

One of the main home remedies that you need to follow to prevent gallstones is a healthy lifestyle. You need to maintain a healthy body weight to prevent gallstones. The following are the best home remedies that will help you to treat and prevent gallstones.

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