Myocardial blood flow and cardiac sympathetic innervation in young adults late after arterial switch operation for transposition of the great arteries

Myocardial blood flow and cardiac sympathetic innervation in young adults late after arterial switch operation for transposition of the great arteries.

Possner M, Buechel RR, Vontobel J, Mikulicic F, Gräni C, Benz DC, Clerc OF, Fuchs TA, Tobler D, Stambach D, Greutmann M, Kaufmann PA.

Int J Cardiol. 2019 Jul 13. pii: S0167-5273(19)32420-9. doi: 10.1016/j.ijcard.2019.07.041. [Epub ahead of print]

PMID: 31337551

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Take Home Points:

  • Disruption of cardiac sympathetic innervation occurs to a variable degree following the arterial switch operation.
  • This small study sought to evaluate sympathetic innervation in young adults after the arterial switch procedure and assess myocardial blood flow at rest and during stress.
  • The study group consisted of 12 patients (age 22.5 +/- 2.6 years) who previously underwent an arterial switch operation and 10 ‘normal’ control subjects (age 22 +/- 1.7 years).
  • PET scanning assessed cardiac sympathetic innervation at rest and under stress.
  • Patients with a previous arterial switch, compared to normal subjects had attenuated sympathetic innervation. Global myocardial blood flow during rest and stress was lower in ASO patients compared to control subjects. 

Commentary from Dr Damien Cullington (Liverpool, United Kingdom), section editor of ACHD Journal Watch:  The arterial switch operation (ASO) was first performed in 1975 by Jatene and superseded the atrial switch with ever increasing frequency from the 1980s. So far, outcomes are very good but, there are important issues which ever increasingly crop up, for example, the dimensional threshold at which to contemplate neo-aortic root replacement (where benefit >risk) and the risk stratification (how and with what frequency) of patients who have kinked re-implanted coronary arteries. Cardiac sympathetic fibres travel with the coronary arteries and the ASO often results in denervation which may consequently alter regulation of myocardial blood flow (MBF). Little has been studied about sympathetic innervation and MBF in adult patients who have undergone the ASO, hence the purpose of this study.

 Assessment of sympathetic innervation and myocardial blood flow

On day one, myocardial blood flow was measured using [15O] H2O PET. Assessments were made at rest, after adenosine stress and following a cold pressor test. On day two, cardiac sympathetic innervation was measured using [11C] meta-hydroxyephedrine (mHED) PET. [11C] mHED is an analogue of norepinephrine – highly specific for pre-synaptic sympathetic nerve terminals. Coronary computed tomography angiography (using a 256 slice high resolution CT scanner) was performed in all patients after mHED PET. Full details of the analysis and calculation of MBF is found in the main text of the article.

 Myocardial blood flow at rest and stress (Figure 1 and Table 1) and cardiac sympathetic innervation

MBF at rest and during adenosine stress was significantly lower in patients with ASO vs healthy controls. No difference in MBF was seen during the cold pressor test. Global [11C] mHED uptake was significantly lower in patients with ASO vs controls (p<0.001).

 

Table 1 – Myocardial blood flow at rest and during adenosine stimulation and during cold pressor test in patients and controls

 Figure 1 – Myocardial blood flow in healthy controls and patients after ASO at rest and during adenosine-induced hyperaemia (A) and at rest and during cold pressor test (B). Comparison of cold pressor test induced myocardial blood flow (C) and mHED uptake (D) between healthy controls and patients.

 Conclusions

The ASO procedure leads to attenuated cardiac sympathetic innervation. MBF response to cold pressor testing did not differ between ASO patients or controls. This is a small study which confirms similar findings in children. Further, large observational studies are needed to assess the natural history and long terms outcomes of patients who undergo the ASO.

 

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