Clinical electrocardiography . Fig. 122.—Electrocardiogram of patient with patent foramen ovale. Markedpreponderance of the right ventricle. Respiratory variation of amplitude of Rwaves especially noticeable in Derivation I. CONGENITAL HEART DISEASE 145 ing and association with other congenital cardiac defects. Whenthe opening in the interauricular septum is small, little or no effecton the circulation is exerted. When the opening is large, andespecially when the left ventricle fails or the pressure in the leftauricle rises, as in mitral stenosis, the blood-current regurgitatesinto the right a
Clinical electrocardiography . Fig. 122.—Electrocardiogram of patient with patent foramen ovale. Markedpreponderance of the right ventricle. Respiratory variation of amplitude of Rwaves especially noticeable in Derivation I. CONGENITAL HEART DISEASE 145 ing and association with other congenital cardiac defects. Whenthe opening in the interauricular septum is small, little or no effecton the circulation is exerted. When the opening is large, andespecially when the left ventricle fails or the pressure in the leftauricle rises, as in mitral stenosis, the blood-current regurgitatesinto the right auricle. This obviously increases the work of theright heart, and frequently the electrocardiograms of these patientsreveal preponderance of the right ventricle (Fig. 122). INTERVENTRICULAR SEPTUM DEFECTDefects of the interventricular septum uncomplicated by othercongenital anomalies are rare. Pulmonic stenosis is the usual. Fig. 123.—Electrocardiogram of patient with congenital interventricularseptum defect. Notched Q R S complexes in Derivations I and II. ExaggeratedP wave in Derivations II and III. Right ventricular preponderance. associated defect. If the defect is associated with pulmonic stenosis,the blood is allowed to pass from the right to the left ventricle,relieving the stress of the former and increasing the work of thelatter. In the uncomplicated defect of the septum the stress ofboth ventricles may be equalized and remain so until one or theother begins to fail from some adventitious cause. It is, therefore,evident that the resulting electrocardiograms may show eitherright or left ventricular preponderance, and in some instancesno imbalance (Fig. 123). 146 CLINICAL ELECTROCARDIOGRAPHY
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