Cardiac resynchronization therapy (CRT), in its traditional form, utilizes simultaneous pacing of the right (RV) and left (LV) ventricles. This is usually achieved by placement of one lead in the RV apex and a second in the coronary sinus (CS), which stimulates the myocardium of the left ventricle. CRT devices attempt to mimic the natural activation sequence and interventricular synchrony in patients with dilated cardiomyopathy with a wide QRS. It has been most effective in those with left bundle branch block (LBBB) and a QRS duration over 150 ms.1-3 The utility of traditional CRT with right bundle branch block (RBBB) is less well defined.4 Recently, His bundle pacing has been proposed as an alternate method of CRT.5-9 This technique is an FDA-approved therapy for pacing. The physiologic benefit of permanent His bundle pacing is the ability to stimulate the ventricles through the native His-Purkinje system, which results in synchronous electrical and mechanical activation. Even in the setting of a RBBB or LBBB, the QRS can often be narrowed with permanent His bundle pacing. Traditional CRT with a CS lead faces numerous technical challenges including inability to place the LV lead, suboptimal anatomy available for left ventricle lead placement, or phrenic nerve stimulation. For those cases, or patients who are considered borderline for a three-lead pacing system, His bundle/para-Hisian pacing could be an excellent choice.
A 76-year-old male with a history of persistent atrial fibrillation (AF), heart failure with preserved ejection fraction, and hypertension presented to the EP clinic with complaint of chronic fatigue. A recent 30-day event monitor showed marked bradycardia. His average heart rates were in the low 40s, with multiple 3-second pauses. He denied any chest pain, orthopnea, paroxysmal nocturnal dyspnea (PND), or syncope. Due to symptomatic bradycardia, the patient was offered pacemaker implantation followed by a rhythm control strategy for his AF. The baseline 12-lead ECG with slow AF, RBBB, and left anterior fascicular block (LAFB) is shown in Figure 1. Due to the high likelihood that he would require chronic ventricular pacing, a His bundle lead (rather than a traditional RV apical lead) was attempted.
Because the proximal His bundle is sometimes difficult to identify during AF, an EP catheter can be used to mark its position before proceeding with the pacemaker implant. Upon arrival to the EP laboratory, the patient was first prepared and draped for femoral access. Using the modified Seldinger technique, a 6 French (Fr) sheath was placed in the right femoral vein. A CRD-2 quadripolar catheter (St. Jude Medical) was used to mark the position of the His bundle. The catheter position was saved in two fluoroscopic views: right anterior oblique (RAO) 25˚ (Figure 2A) and left anterior oblique (LAO) 40˚ (Figure 2B).
Figure 3 shows a screenshot from the CardioLab Recording System (GE Healthcare), demonstrating a His signal recording on the quadripolar catheter and the surface QRS duration (131 ms) during AF. On the second screenshot (Figure 4), para-Hisian pacing from distal electrodes of the His catheter is demonstrated. It can be seen that a much narrower QRS complex is achieved when compared to the patient’s native complex. The pacing threshold was less than 4 mA with a pulse width of 0.2 ms.
The patient was then prepared and draped for insertion of the device and permanent pacemaker leads. An 5076-52 CapSureFix Novus MRI 5076 lead (Medtronic) was passively positioned into the RV apex in the event that backup ventricular pacing was needed during the case. The 4.1 Fr, lumenless, exposed helix SelectSecure model 3830 lead (Medtronic) was used in conjunction with the fixed-curve C315 His sheath (Medtronic). A steerable SelectSite C304-169 catheter (Medtronic) is also available for His bundle lead placement. The fixed sheath is generally adequate for a normal-sized right atrium and a good choice for a mild or moderately dilated right atrium. The steerable sheath may be a better option for severely dilated atria; however, increasing the curvature may result in a limited ability to reach the His bundle. There is no doubt that these tools can be improved upon in the future, especially for patients with enlarged hearts.
Using the quadripolar catheter as a guide, the His bundle lead was used to map for a His bundle signal. A screenshot from the Medtronic pacing system analyzer (PSA) is shown in Figure 5. In the middle channel (atrial electrogram), before the second QRS complex, a small upright deflection can be seen, which represents depolarization of the His bundle. The recording signal is unipolar and it is processed on the Medtronic PSA atrial channel for increased sensitivity to detect the His bundle potential. A satisfactory position was found after several tries. After finding a suitable location, manual rotation (up to 10 turns) was applied to the active fixation lead in order to secure it to the myocardium. Withdrawing the guide sheath ~5 cm and advancing some slack into the lead confirmed that the lead was securely adhered to the myocardium. Next, the delivery system was removed using a standard slitting tool. The technique used is the same as that for CS delivery systems. The atrial lead was then withdrawn to the right atrium and advanced under fluoroscopic guidance using preformed stylets in the right atrial appendage.
Figures 6A and 6B show the final fluoroscopic position of the His bundle lead after placement. At this point of the case, the CRD-2 catheter was displaced from its original para-Hisian position. With this lead position, myocardial capture can result in pure His bundle capture, pure RV septal capture, or as seen in this case, a combination of the two, giving para-Hisian capture.
Testing in this position (Figure 7) showed that the para-Hisian pacing threshold was less than 3 V with a pulse width of 1.0 ms and the QRS duration in the range of 100 ms. After the appropriate lead slack was adjusted, the leads were sewn down and attached to the appropriate port of the dual-chamber pulse generator. The device was placed in the previously created pocket and closed with absorbable sutures in three layers.
The next day, device interrogation found a para-Hisian capture threshold of 2.75 V with a pulse width of 1.0 ms and RV septal capture of 1.0 V at a pulse width of 1.0 ms. The 12-lead ECG in Figure 8 shows para-Hisian capture with a much narrower QRS complex than baseline (98 ms). The baseline RBBB and LAFB have been eliminated.
Permanent His bundle/para-Hisian pacing can be used to achieve a narrow paced QRS even in the setting of existing conduction disease. This offers another method of cardiac resynchronization and may be preferable to right ventricular apical pacing, especially for patients who are expected to have a significant pacing burden. Marking the position of the His bundle with an EP catheter can sometimes assist in mapping of the His signal and lead placement, particularly during atrial fibrillation.
Disclosures: The authors have no conflicts of interest to report regarding the content herein. Outside the submitted work, Dr. Verma reports speakers’ honoraria from Medtronic.
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