Clinical electrocardiography . Fig. 76.—Partial block, 2 : 1 rhythm. Electrocardiogram in Derivation Fig. 77.—Varying degree of partial block, 2 : 1 and 4 : 1 rhythm. Electrocar-diogram in Derivation III. degree of partial block varies from cycle to cycle, when a grossirregularity results. The irregularity at times is total and clinicallycannot be distinguished from auricular fibrillation (Figs. 75 to 77). DELAYED AURICULOVENTRICULAR CONDUCTION The normal conduction time- -between the auricles and theventricles (P-R interval) does not exceed second. Manyobservers consider second
Clinical electrocardiography . Fig. 76.—Partial block, 2 : 1 rhythm. Electrocardiogram in Derivation Fig. 77.—Varying degree of partial block, 2 : 1 and 4 : 1 rhythm. Electrocar-diogram in Derivation III. degree of partial block varies from cycle to cycle, when a grossirregularity results. The irregularity at times is total and clinicallycannot be distinguished from auricular fibrillation (Figs. 75 to 77). DELAYED AURICULOVENTRICULAR CONDUCTION The normal conduction time- -between the auricles and theventricles (P-R interval) does not exceed second. Manyobservers consider second the upper limit of normal, althoughI believe that second conduction time not infrequently isobserved in normal hearts. Delay in impulse transmission through the bundle may be theresult of injury by disease, or by depression of its activity byvagus stimulation. Digitalis given to full physiologic effect alsodelays conduction by its action on the vagus. In the electrocardiogram the P-R interval shows prolongationbeyond second. Neuhof published an electrocardiogram IOO CLINICAL ELECTROCARDI
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