Using Electrocardiographic Activation Time and Diastolic Intervals to Separate Focal From Macro–Re-Entrant Atrial Tachycardias

OBJECTIVES: This study was designed to separate focal from atypical macro-re-entrant atrial tachycardia (AT) on the electrocardiogram (ECG). BACKGROUND: Focal AT often cannot be distinguished from macro-re-entrant AT until the time of electrophysiology study (EPS). We hypothesized that quantitative ECG metrics should separate focal AT, using its short activation relative to tachycardia cycle length (CL), from macro-re-entrant AT, whose activation should span the CL. We developed tools to accurately quantify CL and P- or F-wave duration even when overlying T waves, then prospectively applied them to patients during focal or macro-re-entrant AT ablation and compared them to the gold standard EPS diagnosis. METHODS: We studied 41 patients (27 men, 14 women) age 57 +/- 17 years. In the training group (n = 20), tachycardia P or F waves overlying T waves were identified from transitions in slope (dV/dt) relative to "expected" T waves generated from scaling of the sinus-rate T-wave. Electrocardiographic P-wave duration agreed with the duration of intra-atrial activation. Autocorrelation was used to estimate ECG atrial CL (p < 0.001). RESULTS: Compared to macro-re-entry (n = 13), focal AT (n = 7) had shorter P waves (115 +/- 31 ms vs. 227 +/- 67 ms; p < 0.001) that were smaller ratios of CL (28 +/- 7% vs. 85 +/- 21%; p < 0.001). Receiver-operating characteristic curve areas for AT were 0.92 for P(F)-wave duration and 0.99 for P(F)/CL ratio. On blinded prospective analysis (n = 21), P(F)-wave duration <160 ms identified focal (n = 7) from macro-re-entrant AT (n = 14) with 90% sensitivity and 90% specificity, and a P(F)/CL ratio <45% gave 86% sensitivity and 98% specificity. CONCLUSIONS: Quantitative ECG indexes of shorter atrial activation and longer diastolic interval separate focal from macro-re-entrant AT without diagnostic maneuvers.