Clinical Cases

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What Becomes of the Broken Hearted?

A case of clinical high-second degree atrio-ventricular block treated via trans-venous ventricular pace-maker implantation 

N E Page BVSc, Rolleston Veterinary Services Ltd

“Abby” Davidson, a ten-year-old, speyed female, black & tan, standard Dachshund, presented to Rolleston Veterinary Services with a recent history of episodes of fainting. During excitement or following mild exercise, Abby would frequently stop and fall over onto her side, recovering normally less than a minute later. Due to these episodes, she was no longer able to join her human companion on daily walks. Previously, she had exercised up to one hour daily with her owner.

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Figure 1: Abby with her human companion

Clinical Examination Findings – 23 May 2006

The only obvious clinical abnormality detected on examination was a significant heart murmur most audible on the left side of the chest. No obvious heart arrhythmia or pulse deficits were noted and the remainder of her exam was unremarkable.

Due to the history and clinical findings pointing to a cardiac disease causing the symptoms observed by her owner, Abby was scheduled initially for chest radiology and cardiac ultrasonography the following week.

Diagnostics – June 2006

Radiology (x-rays) showed a rather rounded, globular and apparently enlarged heart and some mild pulmonary oedema (fluid within lungs) was visible. The vertebral heart score (a method of assessing heart size) was within the normal range at ten.

Cardiac ultrasonography showed normal heart chamber sizes, and apparently normal myocardial (heart muscle) wall thicknesses. However, the heart chambers (atria and ventricles) were intermittently seen to be beating out of time during the ultrasound procedure.

An ECG was subsequently performed to investigate this apparent irregularity in contractions of the heart chambers. The ECG revealed a significant failure of electrical transmission between the atria and the ventricles (A-V nodal or Bundle of His failure, with numerous escape complexes), resulting in irregular and abnormal timing of the heart pump (figure 2).

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Figure 2: ECG Lead II trace at 25mm/sec and 10mm/mV

Initial Management

Based on the clinical findings, Abby was initially started on medication to control the mild fluid build-up in her lungs, and options were discussed with her owners for management of her irregular heart rhythm.  Due to our relatively unique position amongst veterinary clinics of owning a C-arm fluoroscope, we were able to offer trans-venous pacemaker implantation for Abby. The ability to perform this procedure under fluoroscopic guidance negates the need for invasive chest surgery.

Discussions were held with Abby’s human companion and her family and everyone was in agreement that this was the best option for Abby and we proceeded to plan her procedure and source a suitable pacemaker and the necessary equipment to enable succesful implantation.

Dr Nick Page contacted the company Guidant, through a local human cardiologist. The Guidant technical representative agreed to supply a pacing lead, and also locate a used pacing unit for us. Due to the novelty of the case along with the fact that he was often down in Christchurch, he also kindly agreed to walk us through the procedure intra-operatively.

Surgery – July 2006

An appropriate anaesthetic protocol was selected for Abby to avoid undue stress on her internal organs due to the detection of elevations in liver enzymes (ALP and ALT) on her pre-anaesthetic bloodwork. Abby was administered the anaesthetic induction agent propofol and maintained under anaesthesia using isoflurane. Both these drugs are also commonly utilised in human medicine for induction and maintenance of anaesthesia. Abby was adminstered supportive intravenous fluids throughout the anaesthetic period, and her blood pressure and heart rhythm (ECG) were continually monitored.

Abby’s right neck was clipped and surgically prepared for aseptic surgery and she was placed in lateral recumbency on our in-clinic fluoroscopy table.

Abby’s right jugular vein was isolated surgically and a needle was inserted into the vein. A flexible guide wire was threaded into the vein through the needle (figure 3).

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Figure 3: A fluoroscopic view of the guide wire with flexible, non-traumatic curved end…this wire is too far caudal and has gone down the posterior vena cava caudal to the diaphragmatic line.

A sheath was then threaded over the wire down to a level just in front of the right atrium of the heart (figure 4).

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Figure 4: The introducer sheath being placed into the right jugular vein

Next, the pacing lead was advanced through the sheath and manipulated into the right atrium (figure 5).

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Figure 5: Fluoroscopic view of pacing lead entering the right atrium

The lead was then manipulated through the right atrium and into the right ventricle. The sheath was then “peeled” out and discarded (figure 6).

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Figure 6: Sheath being “peeled” out and removed from the right jugular vein

From here the pacing lead was threaded down into the bottom of the right ventricle where a turning mechanism was manually activated via a twisting instrument to screw the pacing lead anchor into the heart muscle at this location (figure 7). The anchor is impregnated with a corticosteroid to minimise inflammatory reaction immediately post-implantation.

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Figure 7: Fluoroscopic image of pacing lead anchored into the apex of the right ventricle

An external pacing device was then used to test the pacing lead, and check that the heart was pacing correctly. It also checked that the voltage selected on the pacing unit to be used was at a correct setting for threshold in Abby (figure 8). The pacing unit we were to put in had been pre-programmed at 120 beats per minute at five volts on a single ventricular pacing cycle.

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Figure 8: External pacer and ECG showing a good paced trace at 120 bpm (beats per minute)

The lead was then secured to the right jugular vein and surrounding tissues (figure 9).

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Figure 9: Pacing lead being secured to the right jugular vein and surrounding tissues using the specialised cuff

The pacing unit was then connected (figure 10) and the ECG trace double-checked for correct pacing of the ventricle.

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Figure 10: Connecting the pre-programmed pacing unit

A pocket was made under the skin (subcutaneous) to fit the pacing unit in the neck area. Enough lead was ensured to avoid undue tension on the anchor within the heart muscle during neck movement and the redundant lead coiled beneath the unit. The unit was then placed in this pocket and secured (figure 11).

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Figure 11: Pacing unit sitting within the sub-cutaneous neck pocket

The surgical site was then sutured closed in a routine manner and Abby was monitored closely during her recovery from anaesthetic. Pain relief was given at the time of surgery and continued orally for 5 days to ensure Abby was comfortable after her surgery.

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Figure 12: Fluoroscopic image of the pacing unit in its final resting place

The following day, Abby showed signs of syncope again in the clinic, despite prior good heart and pulse rates. Further fluoroscopic examination revealed the anchor mechanism in the lead had failed, and unwound itself. The lead had hence dislodged from the heart muscle.

The Guidant technician kindly supplied us with a new lead, which we replaced the first one with, using an identical surgical procedure. Once finally anchored in the correct place, things have gone as expected initially.

The following day the pacing unit was checked remotely via a programming device supplied by the technical rep. All was deemed to be functioning fine and battery life was determined to be OK for another five and a half years.

Since her final surgery, Abby has not had one fainting (syncope) episode and is back to her old exercise regime, is losing weight and is playing with toys she “hasn’t bothered playing with for some time”.

At her last re-visit on 7 September 2006, she was bright, alert and responsive and had a heart rate of 120 bpm. She had an obvious heart murmur and was maintained on heart medications in an attempt to alleviate the speed of development of any congestive heart failure secondary to valvular insufficiency causing the heart murmur.

Abby is now exercised in a “halti” rather than a lead and collar in order to avoid any traumatic effects on her neck placed pace-maker.

Acknowledgement

All of us at Rolleston Veterinary Services Ltd. would like to thank Guidant’s Peter Liggins for his kind and patient assistance with this case.

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