RT Book, Section A1 Zimmerman, Franklin H. SR Print(0) ID 1200100053 T1 Chamber Enlargement T2 ECG Core Curriculum YR 2023 FD 2023 PB McGraw Hill Education PP New York, NY SN 9780071785211 LK accesscardiology.mhmedical.com/content.aspx?aid=1200100053 RD 2024/03/28 AB The electrocardiogram (ECG) provides vital clues to the size of the cardiac chambers, which may enlarge in response to a variety of cardiac disorders. Electrocardiographic evidence of chamber enlargement represents an abnormal increase in mass, which may be due to hypertrophy of the muscular walls, dilation of the internal cavity, or a combination of both processes (Figure 7-1). Concentric hypertrophy is a circumferential increase in the wall thickness relative to the internal dimension of the myocardial chamber. This is the characteristic response to pressure overload, where the heart is forced to pump against increased resistance. Cardiac enlargement may also result from dilation, which is an increase in the internal chamber dimension. Eccentric hypertrophy is the adaptive response of the heart to volume overload, where the heart needs to pump an added quantity of blood with each contraction. In this situation, wall thickness increases proportional to the degree of dilation. Cardiac disorders frequently involve both pressure and volume overload; therefore, enlargement of either the atria or ventricles may involve both hypertrophy and dilation.