An Ectopic Primary Pacemaker in Association with Isolated Persistent Left Superior Vena Cava.

We are reporting a case of a young Nepalese man, who was not known to have any past medical history, and who presented with palpitations. An electrocardiogram showed negative P-waves atrial rhythm in II, III, arteriovenous fistula, and V3-V6 with a variable block at 90-130 bpm. No positive "normal" P-waves were demonstrated in any tracing. He was found to have a congenital absence of the right superior vena cava (RSVC) along with persistent left superior vena cava (PLSVC) a condition also called isolated PLSVC (IPLSC). He underwent a treadmill stress test for further evaluation which showed a normal chronotropic response and the same persistent negative P-waves morphology. An invasive electroanatomical and activation mapping showed an absence of RSVC, the earliest atrial activation site in the anterior side of the inferior vena cava (IVC), and the absence of normal (positive) P-waves/normal sinus node (SN) activation. Considering all the available clinical data together, we believe that the patient was living with an ectopic pacemaker node that acts as a primary node and originated in the IVC/right atrium instead of the normal expected SN position. Given the high risk of complete sinoatrial nodal block in case of radiofrequency ablation, the patient was kept on medical treatment with a beta-blocker which was effective in controlling his symptoms and atrial arrhythmia. Copyright:

INTRODUCTION

The presence of left superior vena cava (LSVC) occurs in approximately 0.3%–0.5% with the presence of right superior vena cava (RSVC).[12] On the other hand, the absent RSVC and persistence of LSVC (PLSVC) are rarer congenital anomalies with a prevalence of 0.1%.[1] This condition is also called IPLSC.

Its incidence is tenfold higher in patients with congenital cardiac anomalies, including atrial septal defect and/or conduction disturbances such as sinus node (SN) dysfunction.[345]

We are reporting a patient who has IPLSVC and an ectopic primary pacemaker. The case reported deals with the importance of imaging and invasive electroanatomical and activation mapping in understanding the pathophysiology of the underlying presenting rhythm.

CASE PRESENTATION

A 20-year-old Nepalese man, who was not known to have any past medical history, presented with palpitations for a 2-week duration. The palpitations were intermittent in frequency, started gradually, and resolved gradually, and not associated with chest pain, shortness of breath, dizziness, or syncope. Another review of the system was not contributory.

On physical examination, he was vitally stable apart from an irregular pulse. The cardiovascular physical exam was unremarkable.

On admission, an electrocardiogram (ECG) showed an atrial rhythm at 97 bpm with negative P-waves in II, III, arteriovenous fistula, and variable block in terms of sinoatrial (SA) exit block (Type 1/Type 2) [Figure 1]. The patient underwent further cardiac evaluation with transthoracic echocardiography which showed normal left ventricular size and function and dilated coronary sinus (CS). The dilated CS was evaluated by an injection of saline contrast through both left and right arms that showed filling of the dilated CS first then right atrium (RA) denoting IPLSVC [Videos 1 and 2]. Transesophageal echocardiography redemonstrated the IPLSVC and confirmed it by injecting saline contrast in the right arm with no other associated abnormalities [Video 3]. Further cardiac evaluation with cardiac magnetic resonance showed no other associated cardiac structural or functional abnormalities. A treadmill stress test using the Bruce protocol was done. The patient achieved 85% of the maximum predicted heart rate according to age with normal chronotropic response to exercise with persistent negative P-waves before, during, and after the exercise demonstrating normal autonomic regulation [Figure 2].

Figure 1

Admission ECG: The ECG showed irregular rhythm (variable block) with negative P-waves in inferior leads and V3-V6 (blue arrows). ECG: Electrocardiogram

Figure 2

Treadmill Exercise ECG: This ECG demonstrates a normal chronotropic response to exercise with persistent negative P-waves before, during, and after the exercise. ECG: Electrocardiogram

The patient underwent a 24-h Holter [Figure 3] that showed the same atrial rhythm with a negative P-wave with a diurnal variation. It also showed the SA exit block (Type 2) that was demonstrated in admission ECG [Figure 1].

Figure 3

24-h Holter record: The Holter showed the same atrial rhythm with negative P-wave with a diurnal variation. As well as the sinoatrial exit block Type 2. (a-Bradycardia; b-Tachycardia/PAC; c-Sinus arrhythmia; d-SA exit block)

The patient underwent electrophysiology study and RA electroanatomical and activation mapping using the BLAZER™ mapping catheter (4 mm, Boston Scientific) and St. Jude Medical EnSite Precision™ cardiac mapping system. Electroanatomical mapping showed absent RSVC. The RA activation and voltage mapping showed that the earliest atrial activation site was in the anterior site of the inferior vena cava (IVC) [Figure 4 and Video 4]. There were no normal (positive) P-waves demonstrated during 12-lead ECGs and endocardial signals recording, pacing maneuvers, or pharmacological testing. As the normal sinus rhythm was not demonstrated in all available 12-lead ECGs and endocardial invasive mapping, we believed that the atrial focus in the IVC could represent an ectopic node that acts as a primary pacemaker for the patient. Therefore, the risk of a complete SA nodal block by radiofrequency ablation on this focus is quite high and could require permanent pacemaker (PPM) implantation, which in turn, carries technical difficulties due to the absence of RSVC. After benefit versus risk discussion and shared decision-making with the patient, he was kept on medical treatment (metoprolol 25 mg orally twice daily). The patient was discharged on regular rhythm at 86 bpm with the same negative P-waves morphology.

Figure 4

Electroanatomical mapping showed the focal earliest atrial activation point in red color

A clinical follow-up with 12-lead ECG after 4 weeks in an outpatient clinic showed that the patient was asymptomatic on beta-blocker with a regular rhythm at 84 bpm with the same negative P-waves morphology as the initial 12-lead ECG presentation [Figure 5]. The patient traveled back to his home country, therefore, no further clinical follow-up was available.

Figure 5

Follow-up ECG after 4 weeks: The ECG showed regular rhythm with negative P-wave in II, III, arteriovenous fistula, and V3-V6 (blue arrows). ECG: Electrocardiogram

DISCUSSION

Symptomatic right atrial arrhythmia is usually treated either by rate control medications or catheter ablation after mapping to assess the site of the earliest activation and therefore treatment or ablation feasibility.

It is known that patients with congenital isolated PLSVC were associated with atrial arrhythmia: two cases were reported from Poland by Peregud-Pogorzelska et al.[6] describing the association of PLSVC with atrial fibrillation (AF) that was treated with cryoablation and pulmonary vein isolation. Another case was reported PLSVC associated with drug-refractory AF, found to have an earliest local activation focus at the floor of the proximal PLSVC that was subsequently ablated.[7]

In 1979, a case report of a man who presented with SN dysfunction and AF associated with absent RSVC was treated with disopyramide 100 mg four times a day. However, he ended up with a pacemaker for bradycardia.[5]

Atrial tachycardia (AT) is a regular atrial rhythm at a constant rate of >100 bpm (P-wave rate is usually between 110 and 250 bpm) originating outside of the SN. Focal ATs are usually paroxysmal and self-limited, although in some patients, focal AT may be present nearly continuously. An abrupt onset or termination (e.g., over three to four beats) favors a focal AT.

In our case report, there was no observation or electrical documentation of any normal electrical activity coming from the usual SN location (normal positive P-waves). The patient 24-h Holter study showed negative P-waves atrial rhythm at an average rate of 68 B/M with diurnal variation with no evidence of abrupt onset or termination of any tachycardia. As well during the TMT, there was a good chronotropic response of negative P-waves during the exercise without evidence of any positive P-waves atrial rhythm other than the one demonstrated at baseline.

Considering all the clinical data together, we hypothesized that the patient was living with a normal function ectopic primary pacemaker in a different location from normal SN, which is likely secondary to his congenital anomaly of IVC. We believe an ablation of this focus may put the patient at a high risk of complete SA block and may require a PPM. Moreover, medical treatment was effective in controlling patient symptoms while reserving the unusual site of what looked like SN equivalent.

This case is the first to report a congenital association of an ectopic primary pacemaker node activity along with the IPLSVC.

CONCLUSION

In association with congenital anomalies of IPLSVC, the patient is living on an atrial rhythm that originated from the low part of the RA with a normal physiological autonomic regulation and chronotropic response at rest and during exercise. Medical treatment was effective to control the arrhythmia without the need for ablation.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initial s will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.