Atrial tachycardia

A 64 yr/male, resident of Karaikal, Pondicherry (South India), came to JIPMER hospital with history of palpitation on and off since last one week along with giddiness. There is no history of syncope, nausea, vomiting, angina, dyspnoea, orthopnea or Paroxysmal nocturnal dyspnoea. Patient was a known  case of Diabetes mellitus and hypertension since last 5 years and was on regular medication. During evaluation in the emergency department patient pulse was around 200 beats per minute, regular in rhythm, normal volume, BP=130/70 mmhg, Respiratory and cardiovascular system were normal. ECG of the patient done in the emergency department is shown below.  

ECG 1 (Click on the image to  enlarge it)

ECG 2 (Rhythm strip)

Narrow complex, regular tachycardia,Rate around 200 beats per minute, Clearly visible P wave not seen, but few doubful P wave are seen in lead II,III,avF, V5,V6, RP interval 180 msec,PR interval 160 msec No significant ST-T wave changes seen.
Diagnosis is ???Long RP tachycardia
Diferential diagnosis = Atrial tachycardia, Atypical AVNRT, PJRT

Patient was given injection adenosine to further both to treat and investigate the cause of tachycardia. Patient was given two times 12 mg injection adenosine. Post adenosine ECG is shown below. Tachycardia terminate for few second but again recur

                Post adenosine rhythm strip of the patient still shows on going tachycardia

So patient was given injection dilzem 15 mg slowly intravenously, tachycardia  rate subsided slowly after few seconds. Patient acheive normal sinus rhythm. ECG of the patient in  sinus rhythm is given below

                                                      ECG 4 (Sinus ECG)

ECG  showing heart rate around 100 beats per minutes,there is presence of normal sinus beats along with few premature atrial contraction, normal PR interval, normal axis, No ST-T wave changes are seen,there is no evidence of pre-excitation in the baseline ecg in the form of delta wave.

Patient underwent EPS/ablation at JIPMER, Cardiology department. EPS was suggestive of Atrial tachycardia with origin from left atrium, posterior in location. Patient underwent successful ablation. Patient also underwent Coronary angiography in view of his risk factor of DM and HTN to rule out coronary artery disease. Coronary angiography was suggestive of Non obstructive coronary artery disease of LAD/RCA. Patient was started on medical management for that.
Lets discuss how to  approach in a patient of Narrow complex tachycardia.

Thank  you.