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Figure 10-68: A midsystolic nonejection sound (C) occurs in mitral valve prolapse and is followed by a late systolic murmur that crescendos to Sj. With assumption of the upright posture, venous return decreases, the heart becomes smaller, the C moves closer to Sj, and the mitral regurgitant murmur has an earlier onset. With prompt squatting, both venous return and afterload increase, the heart becomes larger, the C moves toward S2, and the duration of the murmur shortens. (From Shaver JA. Examination ofthe Heart, Part IV: Auscultation. Dallas: American Heart Association; 1990:13. Reproduced with permission from the publisher and the authors.)

In general, maneuvers that decrease LV volume-such as sitting, standing, or strain of the Valsalva maneuver-cause the click to move closer to Sj. Maneuvers that increase LV volume move the click toward S2 (see Chap. 58).

Although the most common cause of nonejection clicks is prolapse of the AV valves, systolic sounds have been reported in patients with left-sided pneumothorax, adhesive pericarditis, atrial myxomas, LV aneurysm, aneurysm of the membranous ventricular septum associated with a VSD, and incompetent heterograft valves. The presence of these conditions usually can be recognized by the clinical setting and by the absence of the typical changes in the timing of the click associated with physiologic and pharmacologic maneuvers.

The Second Heart Sound

Leatham240 has emphasized the importance of the S2 in the cardiac examination by labeling it as the "key to auscultation of the heart." To appreciate the significance of the normal and abnormal S2, knowledge of its relationship to the hemodynamic events of the cardiac cycle is essential.241'242 Figure 10-69 records the two components of S2 simultaneously with the cardiac cycle by high-fidelity catheter-tipped micromanometers. The A2 and P2 are coincident with the incisura of the aorta and pulmonary artery pressure trace, respectively, and terminate the LV and RV ejection periods. RV ejection begins prior to LV ejection, has a longer duration, and terminates after LV ejection, resulting in P2 normally occurring after A2. RV and LV systole are nearly equal in duration, and the pulmonary artery incisura is delayed relative to the aortic incisura, primarily due to a larger interval separating the pulmonary artery incisura from the RV pressure compared with the same left-sided event. This interval has been called the "hangout" interval, a purely descriptive term coined in our laboratory over 15 years ago. Its duration is felt to be a reflection of the impedance of the vascular bed into which the blood is being received.243 Normally, it is less than 15 ms in the systemic circulation and only slightly prolongs the LV ejection time. In the low-resistance, high-capacitance pulmonary bed, however, this interval is normally much greater than on the left, varying between 43 and 86 ms, and therefore contributes significantly to the duration of RV ejection. Awareness of this interval is essential for proper understanding of normal physiologic splitting and for the abnormal splitting seen in conditions where significant alterations in pulmonary vascular impedance have occurred.

Incisura The Arterial Pressure Trace

Figure 10-69: The cardiac cycle recorded by high-fidelity catheter-tipped micromanometers. The aortic (A2) and pulmonic (P2) closure sounds are coincident with the incisurae of their respective arterial traces. Although the LV and RV mechanical systoles are nearly equal in duration, the RV systolic ejection period terminates after LV ejection because of an increased right-sided "hangout" interval. (From Shaver JA. The second heart sound: Newer concepts: I. Normal and wide physiological splitting. Mod Concepts Cardiovasc Dis 1997; 46:7. Reproduced with permission from the American Heart Association and the authors.)

Figure 10-69: The cardiac cycle recorded by high-fidelity catheter-tipped micromanometers. The aortic (A2) and pulmonic (P2) closure sounds are coincident with the incisurae of their respective arterial traces. Although the LV and RV mechanical systoles are nearly equal in duration, the RV systolic ejection period terminates after LV ejection because of an increased right-sided "hangout" interval. (From Shaver JA. The second heart sound: Newer concepts: I. Normal and wide physiological splitting. Mod Concepts Cardiovasc Dis 1997; 46:7. Reproduced with permission from the American Heart Association and the authors.)

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Essentials of Human Physiology

Essentials of Human Physiology

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