Effects of Antegrade Accessory Pathway Conduction on QRS Terminal Vector in Patients with Preexcitation Syndrome

Discrimination between ventricular tachycardia and wide-QRS preexcited tachycardia

BACKGROUND

To develop a new algorithm to differentiate ventricular tachycardia (VT) from preexcited tachycardia (pre-ET) according to left bundle branch block (LBBB) and right bundle branch block (RBBB) patterns.

METHODS

This study included 67 electrocardiograms (ECGs) with VT and 63 ECGs with pre-ET, collected from our hospital and through PubMed. Of those, 64 were allocated to the derivation cohort and the rest to the validation cohort. The diagnoses of the ECGs were confirmed using an electrophysiological study. Parameters and classifiers from prior algorithms along with the propagation speeds in the early portion of the QRS complex (initial deflection index) in leads V1, V6, aVR, II, and III were manually measured. The performance of the new algorithm was compared with that of prior algorithms.

RESULTS

The initial deflection index in lead III was the strongest predictor of pre-ET in LBBB-pattern wide-QRS tachycardia (p = 0.003, AUC 0.805). The initial deflection index in lead V1 was the most powerful predictor of pre-ET in RBBB-pattern wide-QRS tachycardia (p = 0.001, AUC 0.848). Compared to earlier algorithms, those using the initial deflection indexes: lead III in LBBB patterns (cutoff value >0.3) and lead V1 in RBBB patterns (cutoff value ≤0.48), demonstrated superior performance in screening VT, with AUC values of 0.828. The initial deflection indexes proved effective as discriminators between VT and pre-ET in the validation cohort.

CONCLUSIONS

In LBBB-pattern wide-QRS tachycardia, the early propagation speed of pre-ET was faster than that in VT. Conversely, in RBBB-pattern wide-QRS tachycardia, it was slower.

Ventricular Preexcitation: An Anomalous Wave Interfering with the Ordered Ventricular Activation

Ventricular preexcitation is a depolarization of the ventricles that occurs before the conventional sequence, and the electrocardiogram is the specific test for diagnosis. A Kent bundle is the paradigm of ventricular preexcitation, and it is associated with short PR, wide QRS and delta wave. This finding is not always very evident, as it can have different degrees of pre-eccitazione; therefore great diagnostic care must be taken in this field. If not properly identified, the pattern of ventricular preexcitation may lead to an incorrect diagnosis. The methodology of precision electrocardiology is able to confront all these aspects.

Preexcitation syndrome: experimental study on the electrocardiogram of antegradely conducting accessory pathway

Background

Preexcitation syndrome is characterized by a dominant delta wave on the baseline electrocardiogram (ECG), resulting from the change in QRS initial vector by the accessory pathway (AP). This study is to explore the effect of ventricular preexcitation on the QRS initial, maximal and terminal vector in an experimental rabbit with preexcitation syndrome induced by programmed electrical stimulation.

Methods

Rabbits (n = 10) were randomized for the experimental model of ventricular preexcitation. Sensing and stimulating electrode catheters were placed in the high right atrium and along epicardial surface of atrioventricular groove of the left ventricular anterior wall, respectively. Programmed premature stimulation S₂ was synchronized with P wave and utilized to stimulate the ventricle. The ECG recorded the electrical activity of the heart. As compared with the QRS complex during sinus rhythm, paced QRS was assessed regarding the initial, maximal and terminal vector. PS₂ interval and PR interval were also measured and analyzed.

Results

Preexcitation was successfully simulated by ventricular pacing in the rabbits, including (1) Complete preexcitation: PS₂ interval was less than PR interval; the difference was more than or equal to 47.00 ± 7.53 ms. (2) Incomplete preexcitation: PS₂ interval was less than PR interval; the difference was less than 47.00 ± 7.53 ms. (3) Incomplete latent preexcitation: PS₂ interval was more than or equal to PR interval; the difference was less than or equal to 13.00 ± 3.50 ms. (4) Complete latent preexcitation: PS₂ interval was more than or equal to PR interval; the difference was more than 13.00 ± 3.50 ms.

Conclusions

The difference in the relative conduction velocity of the atrioventricular node versus the AP pathways determines the degree of preexcitation and different manifestation on ECG. The QRS terminal vector also reflects the ventricle preexcitation, indicating a valuable sign for the diagnosis of atypical or latent preexcitation.