Abstract
- 1.
Atrial switch (Mustard’s and Senning’s operation) patients can have complex plumbing and electrical issues. Proactive attention to both issues is important to reduce morbidity and mortality, to maintain quality of life, and to extend their longevity as much as possible.
- 2.
The number and size of pacing leads traversing through the superior baffle should be minimized to reduce the risk of baffle stenosis/occlusion. Baffle stenosis should be addressed before lead implantation.
- 3.
Most patients in this group do not need ventricular pacing. Ventricular pacing can increase the risk of dyssynchrony-induced ventricular dysfunction and should be avoided if possible.
- 4.
If ventricular pacing is unavoidable (mostly due to the rare presence of complete heart block), biventricular pacing should be considered in order to minimize dyssynchrony.
Key words
Baffle obstruction, Brady-tachy syndrome, Cardiac resynchronization therapy, Mustard’s operation, Transposition of the great arteries, Ventricular dyssynchrony
Case Synopsis
A 30-year-old female was referred to the congenital heart disease arrhythmia service in 2016. Diagnoses were transposition of the great arteries (TGA), bilateral superior vena cavae [with a left superior vena cava (SVC) draining into the systemic venous atrium (SVA) with no bridging vein], and Crohn’s disease. She underwent atrial septostomy soon after birth and again at 5 months (balloon and blade, respectively), followed by a Mustard operation with a bovine pericardial patch aged 11 months. Postoperatively she developed persistent complete heart block with a narrow escape of ∼60 bpm; however, there was no hemodynamic compromise, and a permanent pacemaker (PPM) was not implanted. Subsequent ambulatory monitoring and exercise testing demonstrated adequate heart rate variability; a 24 h ECG in 1995 (aged 9) showed complete heart block throughout, with a minimum heart rate of 38 bpm and maximum of 133 bpm, the daytime rate being consistently between 70 and 80 bpm. On exercise testing, also in 1995, a maximum heart rate of 145 bpm was reached.
Other than infrequent but severe migraines, she remained well until ∼2004–05 when she started to experience shortness of breath on exertion with a suggestion of some mild systemic venous baffle stenosis on transthoracic echocardiogram (Vmax 2 m/s). This was felt to be dynamic, however, and possibly due to the mitral valve motion. Resting ECG at this time is shown in Fig. 14.1 . She underwent an exercise test (2005) during which she exercised for 9 min of the Bruce protocol, achieving a maximum heart rate of 141 bpm (70% predicted); resting blood pressure was 100/70 mmHg, with no significant rise (peak blood pressure 105/70 mmHg), and maximum workload was 10 METS. The test was stopped due to fatigue, neck pain, and dizziness. There were also multiple ventricular ectopics. At this time her echocardiogram showed the systemic right ventricle (SRV) was mildly dilated with mild systolic dysfunction. A pacemaker was considered but not implanted.
By 2007 her symptoms of breathlessness had worsened such that she was easily short of breath on minimal exertion and also complained of tiredness and occasional light-headedness. A decision was made to go ahead with dual-chamber PPM implantation, prior to which she underwent cardiac magnetic resonance imaging and catheterization in order to fully assess her anatomy, particularly that of her baffle pathways. These investigations identified that there was in fact a stenosis of the superior systemic venous pathway at its entrance to the systemic venous atrium, as well as a significant communication/leak immediately adjacent to the stenotic area between the systemic and pulmonary venous atriums (PVAs). As the leak was proximal to the obstruction, flow was predominantly right to left (Qp:Qs 0.84), and the expected flow acceleration at the site of the SVC narrowing was, therefore, not observed. The pulmonary venous pathway was unobstructed. Systemic right ventricular function was good, and its indexed end diastolic volume was 120 mL/m 2 [indexed left ventricular (LV) end diastolic volume = 78 mL/m 2 ]. The right femoral vein was found to be occluded. It was noted in retrospect that saturations on room air had previously been documented as low as 92%.
She underwent successful stenting of the SVC/SVA junction stenosis with exclusion also of the SVA to PVA baffle leak with a covered stent. There was an excellent angiographic result, although it was noted that the right SVC was of a relatively small caliber. Postprocedure oxygen saturations were 98%–99% on room air. After the procedure she complained of some chest discomfort and developed new T wave inversion on 12-lead ECG ( Fig. 14.3A ) accompanied by a small troponin rise (Troponin T 0.17 ng/mL) but she was otherwise well. Echocardiography repeated the day after the procedure (before pacemaker implantation) demonstrated a moderately dilated SRV with moderate-severe systolic dysfunction, which appeared to be a new finding. There was mild systemic atrioventricular (AV) valve regurgitation. It was unclear as to why the SRV had deteriorated, although it was postulated that it may be as a result of the increased preload; however, a thromboembolic phenomenon could not be excluded. A right-sided dual-chamber pacemaker was implanted uneventfully a few days later. Both leads were active fixation and had satisfactory parameters at implant. The (subpulmonary, left) LV lead was placed apically. Chest X-ray and CT imaging illustrating her stent and pacing leads in situ are shown in Fig. 14.2 . Pre- and postprocedural 12-lead ECGs are shown in Fig. 14.3 . After pacemaker implantation, she was 100% ventricularly paced with ∼30% atrial pacing, with a base rate set at 50 bpm. An exercise test was performed (2008) (bike 5–10W ramp) during which she exercised for over 9 minutes 5 seconds, reaching a maximum heart rate of 163 bpm (82% predicted)—and was atrially sensed, ventricularly paced throughout; VO 2 max was 16.5 mL/min/kg (45% predicted); peak watts 60; VE/VCO 2 slope 33.4 (predicted 23.5); RER 1.04. Blood pressure at rest was 110/70 mmHg, rising maximally to 130/70 mmHg. Height at this time was noted to be 163 cm and weight 48 kg. The test was stopped due to tired legs and shortness of breath.
Although she reported only NYHA class II symptoms, her history appeared to be somewhat unreliable, her lifestyle relatively inactive, and objectively her systemic ventricular systolic function had clearly deteriorated; transthoracic echocardiography in 2008 demonstrated the right ventricle to be moderate-severely dilated and impaired. Serial echocardiographic qualitative data on her SRV available from the reports are shown in Table 14.1 . The precise cause of this deterioration was unclear. Subpulmonary ventricular function was preserved. She was started on ramipril 5 mg once daily; however, this caused a cough and was changed to losartan. On subsequent pacing checks there were no tachyarrhythmias detected and good heart rate histograms.
| 16/11/05 | 21/2/07 | 6/7/07 | 14/4/08 | 18/7/11 | 10/9/12 | 25/2/13 | 5/6/15 | |
|---|---|---|---|---|---|---|---|---|
| SRV size | Mildly dilated | Mildly dilated | Moderately dilated | Moderate-severely dilated | Severely dilated | Severely dilated | Severely dilated | Severely dilated |
| SRV function | Good | Mild dysfunction | Moderate-severe dysfunction | Moderate-severe dysfunction | Moderate dysfunction | Moderate dysfunction | Moderate-severe dysfunction | Severe dysfunction |
A generator change was required in 2012. A transvenous biventricular device was considered at this time; however, it was understood that there was no access to the coronary sinus (CS) via the systemic venous circulation (although interpretation of the CT images of her coronary/left SVC anatomy was felt to be difficult). By 2013, her symptoms had progressed and she was in functional class III. Her echocardiogram demonstrated a severely dilated and moderate-severely impaired systemic ventricle. At this time, her heart failure medications titrated up to the maximally tolerated doses, which subjectively did appear to improve her functional status. During a repeat exercise test in 2013 (bike 5–10 W ramp) she managed only 6 min 52 s of exercise, but the test was stopped due to heart rate limitation as a result of the programmed max tracking rate of the pacemaker (heart rate dropped from 153 to 130 bpm with 2:1 AV block and accompanying shortness of breath). Because of this, interpretation of the data was limited. Heart rate at rest was 84 bpm. The rhythm was atrially sensed, ventricularly paced throughout; VO 2 max was 16.3 mL/min/kg (49% predicted); peak watts 45; VE/VCO 2 slope 43.5 (predicted 24); RER 1.03. Blood pressure at rest was 120/80 mmHg, rising maximally to 130/80 mmHg. Height at this time was noted to be 163 cm and weight 52 kg. She underwent cardiac catheterization in 2014. Results were as follows:
Saturations (%): IVC 78.3, SVC 63.0, LV 70.2, PA 68.0, RV 98.3
Pressures (mmHg): RA 6, LV 35/7, PA mean 16, PCWP 6, RV 113/9, Ao 123/61
Calculations: TPG 9, CO (Fick) 2.49 L/min, CI 1.62 L/min/m 2 , PVRI 5.6WU
CT scan showed at least moderate obstruction within the SVC stent. An epicardial (surgical) attempt at cardiac resynchronization therapy (CRT) was considered, but it was felt that this may be difficult without any certainty of benefit and instead she was referred to the regional transplant center for assessment. There, however, it was felt that she did not fulfill the criteria for transplant at the time based on symptomatology and functional status. Clinical observations were weight 48 kg, BP 112/76 mmHg, sats 98% on air, JVP +2 cm, no peripheral edema detectable, a 2/6 pansystolic murmur was heard, her chest was clear, and there was a 2 cm hepatomegaly with no ascites. Medications were spironolactone 25 mg daily, carvedilol 25 mg twice a day, losartan 150 mg daily, furosemide 20 mg daily, and digoxin 125 mcg daily. Her renal function was normal.
Between 2013 and 2015, the patient also suffered significant flare-ups of her Crohn’s disease, which required treatment and subjectively became her predominant problem. When seen again after an interval for follow-up in the congenital heart disease clinic in 2015, she reported that her cardiac symptoms had improved significantly with medical therapy. A single reported syncopal episode did not correspond to any arrhythmia detected on device interrogation but sounded more likely to be vasovagal in nature, although the exact cause was unclear. Her resting ECG at this time is shown in Fig. 14.4 . In 2015 she also presented to her local hospital with a left-sided hemiparesis which resolved after 2 days and was felt to be consistent with a transient ischemic attack. She was commenced on apixaban. Subsequent device check did not show any arrhythmia.
2016
The patient was referred to the congenital heart disease arrhythmia service in early 2016 following another syncopal episode. This event occurred unprovoked while out walking and was precipitated by chest pain and palpitations. By the time of paramedic arrival, the patient had regained consciousness and was not tachycardic. Pacemaker interrogation showed 10 atrial mode switch episodes due to atrial tachycardia (AT), all occurring for <1 min with CLs 280–400 ms (mainly regular, but some faster episodes irregular) and ventricular pacing up to the maximum tracking rate of 160 bpm. An example is shown in Fig. 14.5 . Ambulatory ECG monitoring was subsequently arranged and also showed frequent brief episodes of max tracking (HR 156 bpm) and periods of bigeminy (junctional/paced rhythm), both of which resulted in symptoms. Transthoracic echocardiographic observations were unchanged.
