The relationship between new cardiac conduction defects and extension of valve infection in native valve endocarditis.

New conduction defects in the setting of native valve infective endocarditis (IE) are commonly believed to be associated with direct extension beyond the free valve area. At University Hospital in Newark, among 100 cases of IE, in none of five instances of associated conduction defects (excluding first-degree heart block) was this the case. In neither of two instances of direct extension of valve infection was this accompanied by a new conduction defect. To explore this relationship, autopsy, surgical, and echocardiographic findings from other institutions were combined with these data. Among 47 instances of new conduction defects in IE, only 60% could be related to direct extension of valve infection. The cause was coronary embolization in 4% and unknown in 36%. Among 119 cases of complicated valve lesions, significant conduction defects were documented by ECG in only 15%. In IE the appearance of new conduction abnormalities may often result from causes other than extension of valve infection. Furthermore, complicated valve lesions may often be present without electrocardiographic evidence, indicating interruption of normal conduction pathways.