Wolff-Parkinson-White (WPW) syndrome is a conduction disturbance characterized by the presence of an accessory pathway between the atria and the ventricles (Kent bundle), which provides an alternative route for ventricular activation [1]. WPW syndrome may occur in patients with a normal heart, but also it can be associated with congenital heart disease (Ebstein's anomaly, atrial and ventricular septal defects, coronary-sinus diverticula) [2]. It is defined by a shortened PR interval (<0.12 second) with normal P wave, wide QRS complex and the presence of a delta wave [3]. The most common arrhythmia associated with this syndrome is the atrioventricular reentrant tachycardia (AVRT). Atrial fibrillation associated with WPW is less common but potentially life-threatening arrhythmia as it can degenerate to ventricular fibrillation (VF). We report a case of wide-QRS tachycardia which was subsequently diagnosed as WPW syndrome with atrial fibrillation (AF) in a patient with situs inversus.

This case is about a 33-year-old, non-hypertensive and non-diabetic female, who was presented to emergency complaining of palpitations without chest pain, dyspnea, or syncope. She had a history of situs inversus with dextrocardia, without associated malformations (Figure 1). On physical examination, pulse rate was 150/min, irregular. Her blood pressure was 80/ 60 mmHg. No other abnormality was detected on physical examination. The electrocardiogram revealed Irregularly irregular, wide-QRS complex tachycardia with broad complexes at a rate of 300/minute (Figure 2). The diagnosis of atrial fibrillation was made. The patient was managed with electrical cardioversion of 200 Joules because of hemodynamic instability. Sinus rhythm was achieved, and the review of the electrocardiogram revealed a short P-R interval and the presence of the delta wave, suggestive of WPW type of pre-excitation syndrome (Figure 3). Transthoracic echocardiography revealed normal echocardiographic findings with normal left ventricular systolic function. She was referred for electrophysiological studies. The accessory pathway was identified and found to be capable of fast antegrade conduction. She was successfully treated with radiofrequency ablation (Figure 4).

In the normal electrocardiogram, P wave represent the electrical activity generated from the sino-atrial node. The electrical impulse then moves to an area known as the atrio-ventricular node (AVN) where is held up for a brief period. This delay is recorded as a PR interval. It represents the time frame from the beginning of atrial depolarization to the beginning of ventricular depolarization. This interval is needed to allow the mechanical emptying of atrial blood into the ventricles. Patients with WPW have a tract that bypasses the AVN known as the Kent bundle. The impulse travels down both the AVN and the Kent bundle, causing early depolarization of the ventricular myocardium and a shortened PR interval on the ECG. The AVN impulse is much faster than transmission of the Kent bundle impulse through the myocardium, and the fusion of the two waves forms a fusion beat with a delta wave on the ECG. The existence of an accessory pathway without the physiological delay of the cardiac impulse in the AVN causes arrhythmias. The most frequent arrhythmia associated with WPW syndrome are paroxysmal supraventricular tachycardia caused by atrioventricular re-entry, and auricular fibrillation (AF) with a rapid ventricular response [4]. Certainly, the ECG is very important in the diagnosis of WPW syndrome and in the localization of the accessory pathway, but it can be mistaken for myocardial infarction, Bundle branch block and ventricular hypertrophy. The appropriate management is based on the risk stratification and the identification of associated conditions [5]. Although the ECG morphology varies widely, especially in the presence of anatomic aberration like situs inversus with dextrocardia, which make the ECG interpretation very difficult. The classic electrocardiographic presentation of dextrocardia consists of [6]:

• Global negativity in lead I.
• Positively deflected QRS complex in aVR.
• Negative P-wave in lead II.
• Reverse R-wave progression in precordial leads.
• Right axis deviation.

To record ECG in situs inversus patient we should reverse the arm leads, reverse V1 and V2 and place the other chest electrodes symmetrically on the right chest in usual intercostal spaces. WPW syndrome is the association of WPW pattern (shortened PR interval and delta wave on the ECG) and episodes of tachycardia. The major risk of WPW syndrome is the frequent development of supraventricular tachycardias whose incidence is reported to be 40–80%. The AVRT is the most common tachycardia in WPW syndrome (75–80%). AF is less common (20–25%) [7].

Treatment of WPW depends on the clinical presentation. For asymptomatic patients with only a documented WPW pattern on their ECG without documented tachycardia, simple conservative observation may be appropriate. Vagal manoeuvres may be used in stable symptomatic patients to block the AVN conduction. But, the mainstay of the treatment of AVRTs consists of interrupting the re-entrant circuit. Calcium channel blockers, beta-blockers and digitalis do not act on the bypass tract, and the transmission through the accessory pathway would increase, with a corresponding increase in ventricular rate. This could have disastrous consequences, possibly causing the arrhythmia to deteriorate into ventricular fibrillation. Hence, it is important to use drugs like class Ic anti-arrhythmics and amiodarone, which act on bypass tract as well as AVN, to terminate AF [8]. A hemodynamically compromised patient with an AVRT or AF must undergo electrical cardioversion. In our case, the electric cardioversion was indicated but because of the dextrocardia situs inversus we had to change the placement of defibrillator pads. In this case, traditional pad placement can be mirrored, or we can use the anterior/posterior placement to the right of the patient's sternum [9]. Significant advances have been made in the field of electrophysiological studies. Radiofrequency catheter ablation has become the treatment of choice for patients with symptomatic tachyarrhythmias with initial efficacy of 95% [10] with a mortality rate between 0% and 0.2% [11].

Wolff–Parkinson–White (WPW) syndrome is the association of WPW pattern and episodes of tachycardia. It is not infrequently encountered in the patient presenting to the emergency department with tachyarrhythmias. We can try medications for symptomatic patients, but the catheter ablation remains the mainstay of the treatment. A particular attention must be paid to patients with dextrocardia situs inversus, especially in ECG record and electrical cardioversion. Recent advances in diagnostic and therapeutic procedures in this field mean that the long-term prognosis for these patients is good.

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