Basic intervals and atrial and ventricular conduction curves

Basic intervals

Basic intervals during sinus rhythm represent a quantitative assessment of the electrical activation of the heart. Normal atrial activation begins at the sinus node, spreads to the low atrium and atrioventricular (AV) junction, and then to the left atrium ( Fig. 6.1 ). Occasionally, the low-right atrium is activated slightly later than the atrium recorded at the AV junction. Activation of the left atrium is mainly through the region of the central fibrous trigone at the apex of the triangle of Koch but also occurs through Bachmann’s bundle, the midatrial septum at the fossa ovalis, and the coronary sinus. In the presence of a normal QRS duration, the normal activation times from the onset of ventricular depolarization to the electrogram recorded from the catheter placed near the right ventricular apex are 5 to 30 ms ( Fig. 6.2 ). The right ventricular (RV) free wall at the insertion of the moderator band into the anterior papillary muscle (apical third of the RV free wall) is typically the earliest site of RV activation and precedes the apical septum by 5 to 15 ms. This depends on if there is continuation of the right bundle branch (RBB) toward the apical septum (<25%) or if the apical septum is activated from Purkinje fibers coming off the RBB in the moderator band. Left ventricular endocardial activation begins at 0 to 15 ms after the onset of the QRS, and the duration of left ventricular endocardial activation ranges from 28 to 50 ms. The midseptum and the inferior wall adjacent to the midseptum are the earliest areas of left ventricular endocardial activation, followed by the superior-basal aspect of the free wall. Activation then spreads radially from these breakthrough sites to activate the apex and then the base at the inferoposterior wall.

Basic intervals during sinus rhythm are measured on the His bundle recording electrograms in sinus rhythm at the usual recording speed of 100 mm/s, although a speed of 200 mm/s may also be used for better accuracy ( Fig. 6.3 ). The most important criterion for reliable measurement is reproducibility. Care should be taken to ensure catheter stability during recordings by means of continuous verification against electrogram characteristics and, if needed, stored fluoroscopic or electroanatomic images