Third-degree atrioventricular block
Unlike benign first-degree atrioventricular block, this condition can cause sudden death and is often associated with serious underlying heart pathology.
- Hypertrophic cardiomyopathy
- Cardiac amyloidosis
- Cardiac lymphoma
- Borrelia spp
- Masticatory muscle myositis
- Duchenne muscular dystrophy
- Golden Retriever Muscular Dystrophy
- Mitral valve endocardiosis
Since there is no conduction between the atria and ventricle, ECG studies usually show a ventricular rate slower (< 40 beats per minute) than the atrial rate (> 60 beats per minute), equating to more P waves than QRS complexes and no relationship between the two. The P-P and R-R intervals are usually constant. The QRS complexes are usually wide and bizarre when the ventricle is supplying the pacemaker, and normal when the escape pacemaker is located in the lower AV junction (above the bifurcation of the bundle of His) in patients without bundle branch block.
This condition should be differentiated from second-degree atrioventricular block.
- Peddle GD et al (2008) Gerbode type defect and third degree atrioventricular block in association with bacterial endocarditis in a dog. J Vet Cardiol 10(2):133-139
- Jung S & Jandrey KE (2012) Hyperkalemia secondary to renal hypoperfusion in a dog with third-degree atrioventricular block. J Vet Emerg Crit Care (San Antonio) 22(4):483-487
- Stern JA et al (2012) Complete atrioventricular block secondary to cardiac lymphoma in a dog. J Vet Cardiol 14(4):537-539