Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content +++ ECG Findings ++ Atrial and ventricular electrical activities are entirely dissociated. The P-P and R-R intervals remain constant. P waves may be hidden in the QRS complex or may distort the shape of the T wave. The atrial rate is usually faster than the ventricular rate, and the ventricular rate is generally slow. +++ Pearls ++ Third-degree block is also called complete heart block because no impulses are conducted from the atria to the ventricles. AV rate and QRS morphology depend upon the location of the escape pacemaker. A nodal escape rate is typically 40 to 60 bpm, with a narrow QRS complex. Ventricular escape rate is usually 20 to 40 bpm, with a widened QRS complex. Complete heart block may be caused by MI, conduction system disease, or drugs such as digoxin. Complete heart block may dramatically decrease cardiac output and cause hypotension. Emergent cardiac pacing is required if the patient is unstable. ++ FIGURE 23.17A Third-Degree AV Block (Complete Heart Block). (ECG contributor: James V. Ritchie, MD.) Graphic Jump LocationView Full Size||Download Slide (.ppt) ++ FIGURE 23.17B The P-P interval is uniform (lower double arrows) and the R-R interval is uniform (upper double arrows), but the P waves and QRS complexes are disassociated. Graphic Jump LocationView Full Size||Download Slide (.ppt) Your Access profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Password? Forgot Username? Sign in via OpenAthens Sign in via Shibboleth You already have access! Please proceed to your institution's subscription. Create a free a profile for additional features.