Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content +++ ECG Findings ++ RBBB with left anterior fascicular block and/or left posterior fascicular block and first- or second-degree AV block. Somewhat of a misnomer, this is not a true blocking of three fascicles; rather, two fascicles are blocked coupled with PR interval prolongation. LBBB plus first-degree AV block is sometimes referred to as trifascicular block as well, but again, only two fascicles are truly blocked in this scenario. +++ Pearls ++ A complete trifascicular block, which includes involvement of all three fascicles, is actually a complete or third-degree heart block. An incomplete trifascicular block technically is a bifascicular block (plus AV block) and may be a precursor to complete heart block. Observation and pacemaker evaluation are warranted, especially if symptomatic. AV-blocking agents can potentiate degree of block. Trifascicular block is usually indicative of primary advanced conduction system abnormalities secondary to coronary artery disease. ++ FIGURE 23.23A Trifascicular Block. (ECG contributor: R. Jason Thurman, MD.) Graphic Jump LocationView Full Size|Favorite Figure|Download Slide (.ppt) ++ FIGURE 23.23B The QRS is wide with RBBB pattern (blue double arrow). Left anterior fascicular block is present (diagonal arrows) along with a prolonged PR interval and first-degree AV block (black double arrow). Graphic Jump LocationView Full Size|Favorite Figure|Download Slide (.ppt) GET ACCESS TO THIS RESOURCE Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth Get Free Access Through Your Institution Contact your institution's library to ask if they subscribe to McGraw-Hill Medical Products. Access My Subscription GET ACCESS TO THIS RESOURCE Subscription Options Pay Per View Timed Access to all of AccessMedicine 24 Hour $34.95 (USD) Buy Now 48 Hour $54.95 (USD) Buy Now Best Value AccessMedicine Full Site: One-Year Individual Subscription $995 USD Buy Now View All Subscription Options