Origin of Electrical Activation Within the Right Atrial and Left Ventricular Walls:

Abstract

Clinical data using the noncontact mapping system (Ensite 3000) suggest that characteristics of the reconstructed unipolar electrograms may predict the origin of electrical activation within the atrial and ventricular walls (endocardial vs myocardial vs epicardial origin). Experimental data are lacking. In ten open-chest pigs (mean body weight 62 kg) cardiac pacing was performed at a cycle length of 600 ms with a pulse width of 2 ms and twice diastolic threshold from the endo-, the myo-, and the epicardium, respectively. Pacing was undertaken at three right atrial and three left ventricular sites, and cardiac activation was recorded with the Ensite system. Reconstructed unipolar electrograms at the location of earliest endocardial activation assessed by color coded isopotential maps were analyzed systematically for differences in morphology. The positive predictive value of atrial electrograms exhibiting an initial R wave during pacing for a subendocardial origin (i.e., myocardial or epicardial) was 0.96. The negative predictive value was 0.48. Electrograms generated during myocardial pacing exhibited increased maximal negative voltage and maximal dV/dt (-3 +/- 1.8 mV, -798 +/- 860 mV/ms, respectively) than the electrograms obtained during endocardial (-2 +/- 1 mV, -377 +/- 251 mV/ms, respectively) and epicardial pacing (-2.1 +/- 0.7 mV, -440 +/- 401 mV/ms, respectively, P<0.01 for both parameters). During pacing at the left ventricular wall, occurrence of an initial R wave did not differ significantly between electrograms reconstructed during endocardial and subendocardial pacing. All other characteristics of the unipolar ventricular electrograms analyzed, except latency, did not differ significantly when compared to stimulation depth. Morphological characteristics of unipolar electrograms generated by the noncontact mapping system during pacing of the atrium allowed for discrimination of an endocardial versus a subendocardial origin of activation. At the ventricular level, characteristics of unipolar electrograms did not predict the origin of cardiac activation in this experimental setting.

Signal Analysis For Cardiac Electrical Activation Studies

“…An initial R wave of the unipolar endocardial electrogram is resulted if the electrical wavefront from a myocardial and an epicardial focus travels in part toward the recording location. In contract to this, in theory an endocardial origin of activation results in a pure QS pattern at the location as all electrical forces are heading away from that location [104]. Therefore, according to this finding it may be stated that the noncontact mapping allows for identification of the origin of focal activation which would be useful in choosing the appropriate mode of energy delivery [105].…”

Modern Electrophysiology Mapping Techniques

“…Critical to this is the excellent temporal resolution inherent to non-contact EAM systems whereby EGMs can be updated at a rate of 1200 electrograms per second. In an animal model, virtual unipolar EGMs from non-contact mapping were able to differentiate between endocardial and subendocardial pacing origins thus providing information on the intramural depth of impulse origin [37]. Unipolar EGMs originating from a sub-endocardial source (i.e.…”