Case Report:
A 71-year-old woman presented with decompensated biventricular heart failure in 2015, thought to be due to acute myocarditis. The CT chest revealed a partial anomalous right upper pulmonary venous drainage, right hypoplastic lung and cardiac dextroposition, findings consistent with Scimitar syndrome. Her ECG revealed LBBB with a QRS duration of 196ms (Figure 1A). She was referred to our institution due to persistent NYHA III-IV symptoms with a severely reduced LV ejection fraction (LVEF) of 25%. Her vasoactive medical therapy was limited by hypotension. Cardiac resynchronization therapy (CRT) was indicated.
In planning for this complex procedure, cardiac CT angiogram and pulmonary venogram revealed right lung hypoplasia and mediastinal shift to the right thoracic cavity leading to dextroposition of the heart chambers. Her left ventricle was severely dilated. The right upper pulmonary vein drained into the inferior vena cava (Figure 1C). The coronary sinus had a high superior take-off but did not demonstrate a left sided superior vena cava. Her previous right heart catheterisation revealed moderately elevated pulmonary artery pressures but only minor left to right shunting with a Qp:Qs of 1.24. The peak systolic and mean pulmonary artery (PA) pressures were 62mmHg and 32mmHg, respectively.
The cardiac CT scan was used to register with the CARTOSEG™ modality of the CARTO (CARTO® 3 Version 6) three-dimensional electroanatomical mapping system. The ventricular septum was found to be rotated anti-clockwise by 60 o due to dextroposition. Fluoroscopic view of RAO 20-30o helped us in orienting the interventricular septum perpendicularly (Figure 2A).
The patient was electively intubated. Using NAVISTAR® DS Bi-Directional Catheter (4mm 7French Curve D-F) and CARTO 3D Mapping system TM (Version 6), images were created, aligned, and verified with the cardiac CT geometries on the CARTOSEG™. Important landmarks like the right atrial appendage, tricuspid annulus, the ostium of the coronary sinus and the His-bundle were tagged (Figure 2B). All the obtained geometries were integrated onto the fluoroscopic screen using the CARTOUNIVU™ modality (Figure 3A-D). A quadripolar catheter was placed in the RV for back-up pacing.
Left-sided delto-pectoral pocket was created. Three separate venography-guided extra-thoracic axillary venous accesses were secured. The axillary vein was then cannulated and a Medtronic® 62cm 6935M high voltage lead advanced to the RV apical septum. CARTOUNIVU™ was used to advance the RV lead to the desired location of the lower septum and the position was confirmed in the RAO 30o and antero-posterior (AP) views (Figure 3A). The cannulation of the coronary sinus (CS) was then attempted. The ostium of the CS was angulated at 90o from usual anatomy, with a sharp superior and anterior tortuosity before reaching the body of the CS (Figure 2B). Neither the standard nor Amplatz curve Attain Command™ and the 90o and 135o Attain Select II™ catheters were successful in cannulating the CS. However, we were successful in advancing a steerable decapolar diagnostic electrophysiology catheter into the CS on which the long sheath was telescoped. We identified 3 tributaries targeted for lead advancement. Unfortunately, all the tributaries had angulation and tortuous take-off precluding successful advancement of any hardware. After multiple attempts with various tools, LV lead placement was abandoned, and His-bundle pacing was attempted.
Placement of the His-bundle lead was guided by the tagged His-bundle anatomy, which was integrated onto the fluoroscopic screen with the CARTOUNIV™. Fluoroscopic angles of RAO 30o and AP were helpful in guiding the Medtronic® C315 catheter to the perceived His-bundle location (Figure 2C). Mapping using the Medtronic® 69cm 3830 pacing lead recorded His-bundle potential at the targeted region (Figure 2D). Passive pacing at the distal His region resulted in a threshold of 5V at 1ms with correction of LBBB (Figure 2E). This resulted in non-selective capture of the His-bundle with complete correction of the LBBB. The threshold for LBBB correction was 1.5V at 1ms and the capture threshold was 0.75V at 0.4ms. Finally, the atrial lead was then placed at the right atrial appendage guided again by CARTOUNIVU™.  A Medtronic® Amplia MRI Quad CRT-D device was secured in the pre-formed left pectoral pocket. The fluoroscopic time was 117 minutes, and procedural time was 350 minutes. The His-CRT was programmed with a LV-RV delay of -80ms and a programmed output of 3.5V at 1.0ms for the His bundle lead. The device mode was set to DDDR 60bpm. The following changes in the 12-lead ECG parameters suggested successful correction of the LBBB by capturing the His-bundle: 1. Narrowing of QRS of 54ms (from 196ms to 142ms); 2. Change in mean QRS axis (from +16o to +42o), and; 3. Decrease in LV activation time (measured in V5 from 90ms to 60ms) (Figure 1B).
The patient returned 6 months post His-CRT-D implantation for review. The lead parameters were satisfactory. She was 99.7% paced. The LBBB correction threshold of the His lead was 2.00V at 1ms. The patient had an improvement in her functional status from NYHA Class III-IV to Class II, associated with a 36% relative increase in LVEF (from 25% to 34%).