Atrial electrograms

Lin J, Scherlag BJ, Zhou J, et al. Autonomic mechanism to explain complex fractionated atrial electrograms (CFAE). J Cardiovasc Electrophysiol 2007 18 1197-205. 

Fig. 1.9 Atrial and ventricular electrograms (EGM) as obtained through a Medtronic Pacing System Analyser Model 5311. Ventricular. Above A typical rS configuration with a minor current of injury pattern. Below The current of injury pattern is more pronounced. Atrial Above A typical rS pattern. Below Approximately 150ms after the atrial electrogram lies a large far-field ventricular electrogram.

All signals are ignored during the absolute refractory period, and noise sampling occurs within the relative refractory period. The purpose of the ARP is to prevent oversensing of the output pulse stimulus afterpotential, the atrial electrogram produced by the atrial stimulus, or ventricular depolarization. 

Fig. 12.2 An example of atrial fibrillation (AF) organizing into atrial flutter. A. The upper strip in the top panel demonstrates the atrial electrogram (EGM) and the lower strip demonstrates the annotated markers indicating how the pacemaker classifies each atrial and ventricular event as well as the cycle length (in ms) between each interval. The atrial electrogram shows the rapid irregular atrial rhythm which subsequently transitions into an organized atrial tachycardia. B. Atrial antitachycardia pacing (ATP) therapy - a burst train followed by two premature extrastimuli is delivered restoring atrial paced rhythm. The marker channel notations indicate how the device classifies each beat. Inter-beat intervals are also shown (in ms). AP - atrial paced event VP - ventricular paced event AR - atrial event sensed in atrial refractory period FS - AF sensed event TD - tachycardia detected TS - tachycardia sensed event. Courtesy AM Gillis.

Fig. 19.2 Assessment of pacemaker dependency, (a) Totally paced ventricular rhythm when the base rate is reduced to 30 ppm in a nontracking (DDI) mode in a patient who has asystoUc complete heart The P waves that occur during the atrial alert period are identified by event markers as are all the ventricular paced complexes, (b) Underlying 2 1 block rhythm is identified in a patient with a DDD pacemaker whose ventricle is normally totally controlled by the permanent pacemaker. To show this, the mode was temporarily changed to VVI and the pacing rate reduced to 30 ppm. The simultaneously telemetered unipolar atrial electrogram is shown along the bottom demonstrating the atrial activity as well as far-field ventricular signals.

Atrial tachycardia (AT) is a rapid ectopic rhythm originating in one of the atria. The onset tends to be sudden. Its rate is usually found between about 130-240 b.p.m., and the rhythm may conduct in a 1 1 fashion to the ventricles. Thus, the rapidly conducted varieties may likely enter the detection zone(s) of the ICD. The atrial electrogram (AEGM) P wave morphology for a dual chamber ICD may show a noticeable change with the onset tachycardia, while the VEGM should remain the same absent BBA. 

FIGURE 6.1 Initiation of atrial fibrillation (AF) with ectopic beats arising from the left superior pulmonary vein (PV). Shown are three surface leads (I, aVF, and VI), five intracardiac electrograms form the coronary sinus (CS prox to CS distal) and five electrograms from a catheter in the left superior PV (PV1 through PV5). After a sinus beat, a premature PV potential appears on PV3, which initiates AF (arrow). 

FIGURE 6.3 Pulmonary vein (PV) isolation. Left panel shows three sinus beats with surface leads aVF, VI, and V6, and ten intracardiac electrograms from the left superior PV (PV-1 through PV-10) before PV isolation. Low amplitude potentials represent atrial activity (small arrow) followed by high amplitude PV potentials (large arrow). Right panels shows elimination of PV potentials after encircling radiofrequency ablation. 

Oral H, Chugh A, Good E, et al. Radiofrequency catheter ablation of chronic atrial fibrillation guided by complex electrograms. Circulation 2007 115 2606-12. 

Figure 24.7 shows an example of a His bundle recording. The top two traces are leads II and Vq of the EGG and the bottom trace is the voltage difference from two electrodes on the indwelling electrode catheter. This internal view of cardiac activation combined with the His bundle electrogram has been referred to as His bundle electrocardiography [20]. Atrial activation on the catheter recording is called the A deflection and ventricular activation called the V deflection. The His bundle potential is the central H deflection. Since the catheter is located very close to the His bundle and AV node, it is assumed that the A deflection arises from atrial muscle tissue close to the AV node. When combined with the surface lead information a number of new intervals can be obtained. These are the PA, AH, and HV intervals. The PA interval is a measure of atrial muscle activation time, the AH interval is a measure of AV nodal activation time, and the HV interval is a measure of the ventricular conduction system activation time. 

FIGURE 15.6 Record stored by an ICD of successful delivery of a defibrillation. An atrial EGM, (top tracing), ventricular electrogram (middle tracing), and ICD marker channel are shown. Markers include ventricular sense (VS), atrial sense (AS), ventricular pace (VP), atrial pace (AP), end of ICD capacitor charge (CE), and delivery of shock (CD). (Reproduced with permission of Medtronic, Inc.)... 

Sensing of intracardiac electrograms. With its broad inter-electrode distance, the unipolar system sees more of the heart in which to detect a spontaneous intracardiac electrical event and thus it was assumed that unipolar was superior to bipolar sensing. In reality, the modem unipolar and bipolar pacing systems show comparable and usually excellent atrial and ventricular electrogram amplitudes and slew rates which usually exceed the standard limits of the sensing circuit by a comfortable margin. 

The pacing calheter is advanced with the balloon inflated while continuously recording the surface ECG and intracardiac electrogram. A large atrial signal... 

Fig. 10.5 Sinus rhythm with second-degree Type 13 2 iniranodal AV block, and RBBB. Note that the AH interval remains constant. TTie HV interval increases from 80 (following first P-wave) to 150ms (following second P-wave). The third P-wave is followed by an H deflection but no QRS complex. AV block occurs in the His-Purkinje system below the site of recording of the His bundle potential (arrow). Note the shorter PR interval after the nonconducted P-wave, a feature typical of Type I second-degree AV block. HBE = His bundle electrogram, A = atrial deflection, H = His bundle deflection, V = ventricular deflection, P = P-wave. TL = time lines 50ms. (Barold SS. Pacemaker treatment of bradycardias and selection of optimal pacing modes. In Zipes DP (Ed.). Contemporary Treatments in Cardiovascular Disease, 1997 1 123, with pamission.)...

Fig. 19.14 Stored atrial and ventricular electrogram from a patient with a Guidant Discovery pacemaker. Although the system interpreted the atrial rate as a paroxysmal supraventricular tachycardia, the close correlation between the atrial and ventricular rates, the PR interval as measured from the recording, and the normal rate identifies this as a normal rhythm. Hence, atrial sensing of the far field R wave probably accounted for the system s diagnosis. Knowing this, one can more effectively program the pacemaker and know how to interpret some of its reports.

Hughes HC, Furman S, Brownlee RR, Del Marco C, Simultaneous atrial and ventricular electrogram transmission via a specialized single-lead system, PACE 1984 7 1195-1201. 

Feuer J, Florio J, Shandhng AH, Alternate methods for the determination of atrial capture thresholds utihzing the telemetered intracardiac electrogram, PACE 1990 13 1254-1260. 

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