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International Journal of Arrhythmia 2014;15(3): 62-68.
Anatomical Obstacles to
Catheter Ablation for
Atrioventricular Nodal
Reentrant Tachycardia



   Radiofrequency catheter ablation (RFCA) is the first choice of treatment for symptomatic AVNRT.1 However, its use in patients with anatomic variations can be complicated. Here, we present two cases of catheter ablation for AVNRT in patients with anatomic variations: an RA septal diverticulum, and lung-disease-induced heart distortion, respectively.

Case 1

   A 22-year-old woman presented with paroxysmal palpitation. Electrocardiography (ECG) revealed narrow QRS tachycardia with a pulse rate of 160 beats/min during palpitation (Figure 1). The patient’s blood pressure was 110/80 mmHg during tachycardia. QRS rhythm was regular and pseudo R’ wave was observed in the precordial lead from V1 to V3. Sinus rhythm was restored following rapid administration of intravenous adenosine (6 mg). The patient had no history of disease or operations. A transthoracic echocardiogram (TTE) showed normal left ventricular ejection fraction (60%) and no structural abnormalities. For electrophysiological (EP) investigation, a 2-mm and a 4-mm quadripolar catheter were used to record His and right ventricular (RV) activity, respectively. Unfortunately, placement of a duodecapolar catheter into the coronary sinus (CS) failed as it could not be advanced into the CS ostium. A right atrial (RA) angiogram was performed for structural analysis (Figure 2). A pouch-like structure was observed in the lower septum of the RA, near the CS ostium. As this structure exhibited contractility, it was diagnosed as a diverticulum, rather than a septal aneurysm. A CS angiogram revealed no association between the diverticulum and the CS (Figure 3). Attempts to place the duodecapolar catheter in the CS were impeded by the diverticulum. An EP study was subsequently performed using a duodecapolar catheter positioned at the RA. Tachycardia was induced after an atrio-His (AH) jump, and atrioventricular and ventriculoatrial conduction exhibited decremental properties. Clinical tachycardia was attributed to slow-fast AVNRT after differential diagnostic maneuvers. A deflectable ablation catheter with a 4-mm tip was positioned at the anterior margin of the CS to ablate the slow pathway. The ablation catheter was found to be unstable yet it was easily moved up and down at the margin of the septal diverticulum. As a result, successful RFCA was only achieved after a considerable time interval.

Case 2

   A 71-year-old man with a tuberculosis-destroyed lung presented with palpitation and dyspnea. Electrocardiography (ECG) revealed narrow- QRS tachycardia with a short RP interval and a pulse rate of 170 beats/min during palpitation (Figure 4). The patient’s blood pressure was 100/70 mmHg at the time of recording, and QRS rhythm was regular. Sinus rhythm was restored following rapid administration of intravenous adenosine (6 mg). The patient had diabetes mellitus, hypertension, and a history of pulmonary tuberculosis. A TTE showed preserved left ventricular ejection fraction (55%) and no structural abnormality. Chest radiography and chest computed tomography showed a severely distorted lung (Figure 5), and counter-clockwise rotation of the heart. In RA angiography, the RA exhibited erect morphology. An EP investigation was subsequently performed using a 2-mm and a 4-mm quadripolar catheter to record His and RV activity, respectively. A duodecapolar catheter was positioned at the CS and the RA. Clinical tachycardia was attributed to slow-fast AVNRT on the basis of EP investigation. Due to the high risk of atrioventricular (AV) block, owing to the patient’s advanced age and distorted heart structure, the ablation focus was carefully considered. First, the lowest level for detection of His potential was identified (Figure 6A, B). Next, a posterior approach was taken, via the middle or posterior septal region near the CS ostium (Figure 6D). His potential was not observed on the electrogram of the ablation catheter (Figure 6C). Energy delivery resulted in successful induction of junctional rhythm, though ablation was immediately aborted on observing ventriculoatrial (VA) conduction block some seconds later. A high degree of AV block with concurrent hypotension occurred. The AV block was initially sustained but eventually recovered after eight hours; the PR interval normalized after two weeks.


   AVNRT is one of the most common tachyarrhythmias, and can be treated by catheter ablation. This can be hazardous when the slow pathway is in close proximity to the normal conduction system. Thus, a clear understanding of cardiac anatomy is essential before AVNRT ablation.
   We have reported two complicated AVNRT cases related to right heart anatomic abnormalities. In the first case, an RA septal diverticulum compromised the positioning and stability of the catheter. Binder et al. analyzed 103 cases of congenital malformations of the RA and the CS.2 Of the 103 cases studied, 13 were associated with an RA single diverticulum and these were predominantly asymptomatic. The presentation of symptoms such as supraventricular tachycardia was frequently induced by arrhythmia.
   We present the first reported case of a single diverticulum in the RA septum. Previous studies have reported cases of RA diverticula predominantly localized to the RA free wall or the CS.2-7 The RA septal diverticulum described in this case was separated from the CS, as demonstrated by the angiogram. Because the diverticulum exhibited contractility consistent with the heartbeat, we ruled out the alternative diagnosis of septal aneurysm, in which contractility would not be observed.8
   Acquired anatomic distortions can also interfere with RFCA for AVNRT. In the second case, safety was ensured by using numerous methods: (1) RA angiogram, (2) confirmation of the lowest point for detection of His potential, (3) a posterior approach near the CS ostium, and (4) vigilant observation of VA conduction. A contemporary transient high degree AV block was nevertheless seen to occur.
   For effective and safe catheter ablation in patients with anatomic obstacles, an overview of the precise anatomy is critical. Angiograms and careful mapping can facilitate the identification of anatomic variants, and can confirm precise catheter positioning.


   We have reported two difficult AVNRT cases related to right heart anatomic variation: the first, an RA septal aneurysm, and the second, heart distortion due to tuberculosis-destroyed lung. Anatomic obstacles can compromise successful catheter ablation for AVNRT.


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