Cardiovascular Journal of Africa: Vol 32 No 6 (NOVEMBER/DECEMBER 2021)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 32, No 6, November/December 2021 AFRICA 293 were: (1) intermittently occurring pre-excitation that was detected in previous ECGs, (2) delta-wave resolution on a treadmill test, (3) presence of multiple accessory pathways, and (4) accessory pathway locations other than the septum. A 12‑lead surface ECG (Nihon Kohden Corporation, Cardiofax M Model ECG-1250, Tokyo, Japan) was performed in the supine position, with a 25-mm/s paper speed and a voltage of 10 mm/s. ECGs were recorded after 15 minutes’ resting. All the ECG papers were scanned and transferred to the digital media, and the digital records were analysed under × 400% magnification in a personal computer. The shortest measured P- to delta-wave interval from V1 and V2 (shorter one acquired) on 12-lead ECG was recorded for each patient (Fig. 1). Measurement started from the beginning of the P wave to the first upstroke (or downstroke if it was negative) of a delta wave. Electrograms (EGM) were retrospectively analysed from recorded procedural data in an electrophysiology stimulator (EP-TRACER, Schwarzer Cardiotek GmbH, Germany). All ECG and EGM measurements were taken separately by two different cardiologists who were blinded to the clinical signs of the patients, and the mean values were transferred to the database. The inter- and intra-observer coefficients of variation were 3.2 and 2.4%, respectively. The institutional protocol for electrophysiological testing was as follows: • Incremental atrial pacing was performed until the highest rate was conducted 1/1 through the accessory pathway and/or the atrioventricular (AV) node. • Programmed atrial stimulation in two different drives (at basic cycle lengths of 400 and 500 ms) was performed: one atrial extra-stimulus was delivered after eight paced atrial stimuli at a cycle length of 400 or 500 ms from 390 or 490 ms until the accessory pathway (AP) refractory period or the atrial effective refractory period (ERP) was achieved with decreases of 10 ms. • Briefly, atrial and ventricular extra-stimulation with progres- sively shorter coupling intervals was performed to induce AV re-entrant tachycardia (AVRT) until the effective refractory periods of the atrium and ventricle were achieved. • The disappearance of the pattern of pre-excitation was indicated when the APERP was reached. The longest atrial decremental pacing interval that failed to conduct at the atria was considered the effective APERP. This protocol was repro- duced again after several minutes to study the reproducibility of the measurement of the anterograde effective refractory period. Inducible arrhythmias were defined as sustained if they lasted more than one minute. Tachyarrhythmia inducibil- ity was defined as reproducible induction of sustained AVRT, or atrial fibrillation (AF), or AVRT conversion to AF. • All interventions listed above were done under conscious sedation with midazolam and phentanyl. Statistical analysis All analyses were performed using SPSS V 22.0 for Windows (SPSS Inc, Chicago, Illinois, USA). The Kolmogorov–Smirnov test was used to determine the distribution of continuous variables. The Student’s t -test or Mann–Whitney U -test was used to compare two means according to whether the data were normally distributed. Chi-squared or Fisher’s exact tests were used to examine categorical variables. Continuous variables are represented as mean ± SD and categorical variables as counts and percentages. A p -value < 0.05 was considered statistically significant. The Spearman correlation coefficient was used for correlation analysis to evaluate relationships between the following parameters: PDI, AF inducibility, APERP and age. Receiver operating characteristic (ROC) curve analysis was applied to determine the sensitivity and specificity with a 95% confidence interval (CI) for the PDI to detect the presence of APERP ≥ 240 ms and AF triggering tachycardia at the cut-off values. The association of different variables with APERP was calculated in univariate analysis. Logistic regression analysis was used to find independent predictors of APERP < 240 ms. Results Baseline demographic, clinical and electrophysiological properties of the study group are listed in Table 1. Among V1 and V2, 71 patients’ PDI were measured shorter on V1 (68%). A total of 103 patients were grouped by APERP. Individuals with APERP < 240 ms were included in group I ( n = 29) and individuals with APERP ≥ 240 ms were included in group II ( n = 74). Table 1. Demographical and clinical data Parameters Age, years 42.6 ± 14.4 Male gender, n (%) 32 (31.1) Hypertension, n (%) 3 (2.9) Diabetes, n (%) 6 (5.8) Structural heart disease, n (%) 5 (4.8) Symptomatic patients, n (%) 57 (55.3) PDI, ms 98.4 ± 9.28 APERP, ms 283.2 ± 35.7 AF triggering tachyardia, n (%) 30 (28.8) AF: atrial fibrillation, APERP: accessory pathway antegrade effective refractory period, PDI: P- to delta-wave interval Fig. 1. P- to delta-wave interval measurement on surface ECG. A: surface ECG of a patient’s right septal acces- sory pathway. B: shortest interval detected on V1 deri- vation. C: comparison of all derivations. A B C