Analysis of ST segment depression in supraventricular tachycardia and its relationship with underlying mechanism

Background

Electrocardiographic diagnosis of causes of supraventricular tachycardia (SVT) is sometimes difficult and application of routine algorithms can lead to misdiagnosis in as many as 37 % of patients. ST segment depression may be useful in diagnosing the nature of SVT.

Methods

We reviewed surface electrocardiogram (ECG) characteristics of 300 patients having SVT with 1:1 AV relationship and correlated findings with electrophysiology study (EPS) findings. Final diagnosis of AVNRT (Atrioventricular nodal reentrant tachycardia), Orthodromic AVRT (atrioventricular reentrant tachycardia) and atrial tachycardia (AT) was correlated with ECG parameters like heart rate, ST segment depressions and QRS morphology.

Results

Out of 300 patients, majority patients included in study, were having AVNRT or AVRT. ST depression predicted AVRT if the ST depression was ≥ 2 mm (overall sensitivity of 38.3 % and specificity of 93.8 % to predict AVRT) and was downsloping in morphology (sensitivity of 36.9 % and specificity of 94.7 % to predict AVRT). At heart rates ≥214 beats per minute (bpm) as measured by 7 small squares of ECG at 25 mm/s, downsloping ST depression ≥2 mm had a sensitivity 37.9 % of and specificity of 89.2 % to predict AVRT. At heart rate <214 bpm, downsloping ST depression ≥2 mm had sensitivity of 37.2 % and specificity of 96.5 % to predict AVRT. Downsloping ST depression of ≥2 mm helps to differentiate AVNRT from AVRT.

Conclusion

A downsloping ST segment depression ≥2 mm predicted SVT being an AVRT and can be used as a useful criteria in diagnosing the tachycardia.