Schematic 12-leads’ ECG mapping for Localization of VT source ; made easy
A 57 years man is brought to you to the ER , BP-about &60mmhg, Bibasilar crackles and drowsy . you diagnosed as “ventricular tachycardia”!!!
1- Now is this patient suitable for targeted EP mapping :substratemappint with EP suit ” ?
2- If yes, what should do next ?
3- If not , what is your next step to “map” the V.Tach origin and to tell for surgeon about its localization ?
Substrate mapping technique
Before to any planned arrhythmia intervention , first must identify the target area for treatment . Usually it’s done with either targeted EP mapping and/or systemic ECG interpretation . using an essential technique of electrophysiologic substrate mapping , a detailed schematic map of the heart is generated .
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This map is generated by measuring endocadial voltage potentials at a variety of locations . In the generated map , voltages greater than 1.5mV represent normal cardiac tissue and appear purple ; voltages less tah 0.5 mV represent dead cardiac muscle and appear red ; and voltages in between represent the borderline ischemic area and are represented by a range of colors .
After substrate mapping is completed the electrophysiologist and surgeon are able to carefully reviews the generated projection and can specifically target the border zone areas of potentially arrhythmogenic substrate for open intra-operative cryoablation at the time of LVAD placement .
Note in figure 1 below the visualized EP mapping catheter at the time of mapping in order to very specifically target the mapped arrhythmogenic substrate in real time .
The main issue here is to point , unfortunately , a hybrid suite is not available at this time and not all patients are stable enough to tolerate transport to , and mapping in , the EP suite . considering this practical issue , electrophysiologists devised a compromise technique for targeting the locus of arrhythmia generating substrate . In patients with hemodynamic instability who would not tolerate substrate mapping in the EP suite , a systematic interpretation of 12-lead EKG results capturing episodes of ventricular arrhythmia is performed . Systematic EKG analysis of captured ventricular arrhythmia event is then used to localize the arrhythmia origin to a anatomic area of the heart (i.e.LV lateral wall ) .
Using figure 2 . as an example of sustained monomorphic VT , one first look at lead v1. If a left bundle branch block (LBBB) is visible , the arrhythmia source comes from the RV or septum, if a RBBB is visible , the arrhythmia is generated in the lV . one cal then look at the direction of deflection of the QRS complex to more specifically localize the arrhythmia focus . first , looking at the inferior leads , II, III, avF , a positive wave localizes the focus to the anterior aspect of the LV . Alternatively , a negative wave indicates posterior LV . similiarly , the precordial leads are analyzed and a positive defelction in avR and v4 indicated an apex source , a negative deflection points to the base of the ventricle . finally , lead I and avL are analyzed , with a positive deflection indicating a septal soure , a negative deflection pointing to a lateral wall source .
IN this manner , the focus of arrhythmogenic substrate can be localized to a specific area of the heart that allows the surgeon to target this area intra-operatively with cryoablation . for example , using strip below , the 12 lead ECG of captured ventricular tachycardia can be used to localize the arrhythmia source to the apical LV postero-septal wall . RBBB points to the LV , then inferior leads points to the posterior surface , then precoardial leads indicate an apical source , then I and avL point to the septum . Therefore , the LV postero-septal wall close to the apex is likely the source .