Left phrenic nerve

The CS drains venous blood from the heart into the right atrium. Many branches from the LV flow into the CS, including those from the lateral and posterior LV. Currently, it is there that a left ventricular pacing lead is optimally placed. This maybe best visualized under fluoroscopy from a left anterior oblique (LAO) perspective. Many patients who are candidates to receive a CS left ventricular lead, however, have had myocardial infarctions that may limit the ability to pace from these sites. Stimulation of the left phrenic nerve during ventricular pacing may occur, and can preclude placement there (the left phrenic nerve travels in close proximity to this cardiac region on its way to the left hemi-diaphragm). 

In 2003 she required surgery unrelated to her respiratory condition. Postoperatively she required intubation and ventilation. When she resumed pacer ventilation, her pacers were turned up to much higher amplitudes, to promote better ventilation. However, her tidal volumes remained low at 320 to 350 cc and during her recovery she used manual ventilation and GPB frequently, to provide comfort, by increasing her volumes to 650 cc. Repeat phrenic nerve conduction studies showed that the left phrenic nerve was not... 

The atrial lead mnst be passed into the systemic venons atrium, which is composed mostly of artificial material in the Mustard procedure. Areas of left atrial tissue are incorporated into the systemic venons atrinm and are available for pacing. The ideal location for placement of an active fixation atrial lead is in the roof of the left atrial portion of the systemic venons atrium, with the lead pointed directly snperior. The tendency of the lead as it crosses the baffle is to be directed against the lateral wall of the left atrium jnst above the mitral annulus, but placement of the lead here almost always allows phrenic stimulation. Directing the lead snperiorly avoids the phrenic nerve (45). 

Figure 7 Twitch transdiaphragmatic pressure elicited by phrenic nerve stimulation (upper panel) and FRC (lowerpanel) in a patient with severe emphysema before (left) and after (right) lung volume reduction surgery. The increase in transdiaphragmatic pressure after surgery was partly due to a decrease in the operating lung volume as demonstrated by the decrease in FRC. Abbreviation FRC, functional residual capacity. Source Data from Ref. 128.

She had minimal maintenance issues for many years, with the exception of transmitter replacements. Her tidal volumes ranged from 450 to 700 cc on minimal amplitude settings (right 2.4 and left 2.5) and a respiratory rate of 12 bpm, to maintain blood gases within the normal range. Routine follow-up phrenic nerve studies showed that conduction time on both sides and the diaphragmatic response to phrenic nerve stimulation was normal. 

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