Rate-dependent ST segment depression--a case report

The retrograde P-wave theory: explaining ST segment depression in supraventricular tachycardia by retrograde AV node conduction

BACKGROUND

Pseudo ischemic ST segment changes during supraventricular tachycardia (SVT) are not yet fully understood. Our aim was to determine whether venticulo-atrial (VA) conduction during SVT may be a possible mechanism for ST depression (STd) in SVT.

METHODS

Patients undergoing SVT ablation (2010-2012) were analyzed (n = 72).Typical atrioventricular node reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT) were included. Those with STd were compared to those without STd. VA interval length, tachycardia cycle length (TCL), and retrograde P-wave activation during SVT were assessed. Retrograde P waves arriving simultaneously with the ST segment (PWST) during SVT were considered, whenever an atrial electrogram (measured from the high right atrium) was "on time" with the ST segment.

RESULTS

Patients with STd during SVT presented longer VA intervals than those without STd (VA 100 ± 37 ms vs VA 69 ± 22 ms; P = 0.006). No differences in TCL were observed (TCL 333 ± 35 ms vs TCL 360 ± 22 ms; P = 0.1). PWST was observed in 38.5% of patients with AVNRT and STd versus 0% in those without STd. The TCL was similar in both groups (355 ± 25 ms vs 334 ± 18 ms; P = 0.1). In patients with AVRT and STd, PWST was present in 81% of cases versus 0% in those without STd. The TCL was also similar (330 ± 29 ms vs 346 ± 17 ms; P = 0.1).

CONCLUSIONS

STd during SVT is observed at long VA intervals when the retrograde P wave matches the ST segment, without dependence on the TCL. This suggests that STd is not necessarily rate dependent but a result of a fusion between the ST segment and the P wave.