Wagner_Marriot's Practical Electrocardiography, 12e

GLOSSARY

which has the capacity for wide variations in conduction time. Wenckebach sequences are the classic form of type I block. Mobitz type II (type II): a pattern of AV block in which there are constant PR intervals despite varying RP intervals. This pattern is typical of block in the ventricular Purkinje system, which is incapable of significant variations in conduction time. RP interval: the time between the beginning of the previously conducted QRS complex and the beginning of the next conducted P wave. RP/PR reciprocity: the inverse relationship between the interval of the last previously conducted beat (RP interval) and the time required for AV conduction (PR interval). This occurs in type I AV block. Second-degree AV block: the conduction of some atrial impulses to the ventricles, with the failure to conduct other atrial impulses. Third-degree AV block: failure of conduction of any atrial impulses to the ventricles. This is often referred to as “complete AV block.” Wenckebach sequence: the classic form of type I AV block, which would be expected to occur in the absence of autonomic influences on either the SA or AV nodes. 5. Narula OS. Wenckebach type I and type II atrioventricular block (revisited). Cardiovasc Clin . 1974;6:137–167. 6. Young D, Eisenberg R, Fish B, et al. Wenckebach atrioventricular block (Mobitz type I) in children and adolescents. Am J Cardiol . 1977;40:393–393. 7. Lenegre J. Etiology and pathology of bilateral bundle branch block in relation to complete heart block. Prog Cardiovasc Dis . 1964;6:409. 8. Lepeschkin E. The electrocardiographic diagnosis of bilateral bundle branch block in relation to heart block. Prog Cardiovasc Dis . 1964;6:445. 9. Rosenbaum MB, Elizari MV, Kretz A, et al. Anatomical basis of AV conduction distur- bances. Geriatrics . 1970;25:132–144. 10. Steiner C, Lau SH, Stein E, et al. Electrophys- iological documentation of trifascicular block

REFERENCES Atrioventricular (AV) block: a conduction abnormality located between the atria and the ventricles. Both the severity and the loca- tion of the abnormality should be considered. Degree: a measure of the severity of AV block. First-degree AV block: conduction of atrial impulses to the ventricles with PR intervals of 0.21 second. Footprints of the Wenckebach sequence: the pattern of clusters of beats in small groups, with gradually decreasing intervals between beats, preceding a pause that is less than twice the duration of the shortest interval. Heart block: another term used for AV block. His-bundle electrograms: intracardiac recordings obtained via a catheter positioned across the tricuspid valve adjacent to the common or His bundle. These recordings are used clinically to determine the location of AV block when this is not apparent from the surface ECG recordings. Infranodal block: AV block that occurs dis- tal to or below the AV node and therefore within either the common bundle or in both the RBB and LBB. Mobitz type I (type I): a pattern of AV block in which there are varying PR intervals. This pattern is typical of block within the AV node, 1. Johnson RL, Averill KH, Lamb LE. Electro- cardiographic findings in 67,375 asymp- tomatic individuals. VII. A-V block. Am J Cardiol . 1960;6:153. 2. Van Hemelen NM, Robles de Medina EO. Electrocardiographic findings in 791 young men between the ages of 15 and 23 years; I. Arrhythmias and conduction disorders. (Dutch). Ned Tijdschr Geneeskd . 1975;119: 45–52. 3. Erikssen J, Otterstad JE. Natural course of a prolonged PR interval and the relation between PR and incidence of coronary heart disease. A 7-year follow-up study of 1832 apparently healthy men aged 40–59 years. Clin Cardiol . 1984;7:6–13. 4. Damato AN, Lau SH. Clinical value of the electrogram of the conduction system. Prog Cardiovasc Dis . 13:119–140.

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SECTION III: Abnormal Rhythms