Quantitative analysis of the duration of slow conduction in the reentrant circuit of ventricular tachycardia after myocardial infarction.

Background: Few data are available to define the circuits in ventricular tachycardia (VT) after myocardial infarction and the conduction time (CT) through the zone of slow conduction (SCZ). This study assessed the CT of the SCZ and identified different reentrant circuits.

Methods: During VTs, concealed entrainment (CE) was attempted. The SCZ was identified by a difference between postpacing interval (PPI) and VT cycle length (VTcl) < or =30 ms. Since the CT in the normally conducting part of the VT circuit is constant during VT and CE, a CE site within the reentrant circuit with (S-QRS)/PPI > or = 50% was classified as an inner reentry in which the entire circuit was within the scar, and a CE site with (S-QRS)/PPI < 50% as a common reentry in which part of the circuit was within the scar and part out of the scar.

Results: CE was achieved in 20 VTs (12 patients). Six VTs (30%) with a (S-QRS)/PPI > or =50% were classified as inner reentry and 14 VTs (70%) with a (S-QRS)/PPI <50% during CE mapping as common reentry. The EG-QRS interval (308 +/- 73 ms vs 109 +/- 59 ms, P < 0.0001) was significantly longer and the incidence of systolic potentials higher (4/6 vs 0/12, P < 0.001) in the inner reentry group. For the 14 VTs with a common reetry, the CT of the SCZ was 348 +/- 73 ms, while the CT in the normal area was 135 +/- 50 ms.

Conclusion: According to the proposed classification, 30% of VTs after myocardial infarction had an entire reentrant circuit within the scar. In VTs with a common reentrant circuit, the CT of the SCZ is approximately four times longer than the CT in the normal area, accounting for more than 70% of VTcl.