Patient V, 25 years old,  admitted to the tachyarrhythmia surgical treatment unit at the Medical Center with the diagnosis "Ventricular premature heartbeats from the output parts of the heart".
On the pre-operational stage monitored around the clock with a Holter ECG there was registered from 25000 to 30000 VPB. The morphology of extrasystolic complex is shown in Figure 1.

Fig. 1.  ECG of patient V., 25 years old (12 leads). Premature heartbeats from the excretory tract of the right ventricle.

The patient underwent Non-invasive EPI of the heart. A typical extrasystolic ventricular complex was selected for calculation.
Isopotential maps revealed a stable region of negative potential spreading concentrically in the anterior septum of the excretory tract of the right ventricle; that proves the presence of ectopic factor in the given zone.  Activation in the endocardium anticipated activation in the epicardium (Fig. 44).
Unipolar electrograms from the region of early activation had a typical QS view (Fig. 45).
After establishment of a negative threshold, "dichromatic" maps in the FND mode were created in the unipolar electrogram, enabling to visualize the dynamics of the beginning of activation spread process (Fig. 46).  Activation break on the endocardial surface appeared at the 264th millisecond from the beginning of the analyzed ECG fragment, break on the epicardial surface appeared at the 268th millisecond. Advance of endocardial activation is 4 milliseconds.  Taking into account a small (3 mm) thickness of myocardium in this zone, this advance indicates subendocardial location of ectopic focus. 
When time interval is being set, isochronous maps were built on the unipolar electrograms (Fig. 47) and activation spread maps (Fig. 48) according to the FND method. These maps show sequence of myocardium activation at the beginning of myocardium activation. 
However, activation maps in the FND mode do not allow tracking the dynamics of ventricular activation during the entire period of depolarization. 
To visualize the full sequence of myocardium activation, activation mapping in the ADM mode was used. After selection of time interval for map building, (Fig. 49.) maps of myocardium activation direction (Fig. 50), isochronous maps (Fig. 51, 52) and activation spread maps were obtained (Fig.  53). 
Vector field of myocardium activation directions revealed typical effect of divergence of vector from the regions of endocardial and epicardial activation breaks. 
According to data of isochronous maps and activation spread maps, activation appeared in the endocardial surface of the anterior-lateral wall of excretory tract of the right ventricle and ended in the posterior walls and in the apical regions of the right and left ventricles. 
The advance of endocardial activation break in the region of early activation is also 4 milliseconds. Projections of the zone centers of epicardial and endocardial breaks are shifted towards each other of 6 mm.  (Fig. 52).
For more acute matching of electrophysiological and anatomical data, the maps of activation spread were build on a voxel model of the heart  (Fig. 54).
Additionally, isochronous maps according to the TID method were built in the "advanced" mode.  The interval selection for map building is shown in Fig. 55.
Isochronous map according to the TID method reveals the same sequence of ventricular activation compared to the AMD method. However, isochronous map according to the TID method has much lower spatial resolution (Fig. 56).
Thus, according to data of Non-invasive activation mapping using different research methods of myocardium activation it is established that the reason for premature heartbeats is an ectopic source located subendocardially in the anterior-septum wall of excretory tract of the right ventricle.
Position of the ectopic focus is highlighted with the markers on the voxel model of the heart (Fig.  57).
Invasive EPI confirmed the determined location of ectopic focus.   The patient underwent effective RFA. The position of ablative catheter is shown in Fig. 58. During postoperative period recurrent of premature heartbeats from the excretory tract of the right ventricle were not observed.

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