Myocardial protection in paediatric cardiac surgery: building an evidence-based strategy

Cardioplegia is fundamental to the surgical repair of congenital heart defects by protecting the heart against ischaemia/reperfusion injury, characterised by low cardiac output and troponin release in the early postoperative period. The immature myocardium exhibits structural, physiological and metabolic differences from the adult heart, with a greater sensitivity to calcium overload-mediated injury during reperfusion. Del Nido cardioplegia was designed specifically to protect the immature heart, is widely used in North America and may provide better myocardial protection in children; however, it has not been commercially available in the UK, where most centres use St Thomas' blood cardioplegia. There are no phase 3 clinical trials in children to support one solution over another and this lack of evidence, combined with variations in practice, suggests the presence of clinical equipoise. The best cardioplegia solution for use in children, and the impact of age and other clinical factors remain unknown. In this Hunterian lecture, I propose an evidence-based strategy to improve myocardial protection during cardiac surgery in children through: (1) conducting multicentre clinical trials of established techniques; (2) improving our knowledge of ischaemia/reperfusion injury in the setting of cardioplegic arrest; (3) applying this to drive innovation, moving beyond current cardioplegia solutions; (4) empowering personalised medicine, through combining clinical and genomic data, including ethnic diversity; and (5) understanding the impact of cardioplegic arrest on the late outcomes that matter to patients and their families.

Adult outcomes of complex pulmonary atresia, ventricular septal defect and major aortopulmonary collaterals following repair during childhood, a single centre experience

Background

Complex pulmonary atresia with a ventricular septal defect and major aortopulmonary collateral arteries (PA VSD MAPCA) is a rare and complex form of congenital heart disease. Staged surgical palliation is carried out in childhood, and in expert centres, is associated with good medium term survival. Adult outcomes following transition to adult care are not known.

Purpose

To establish adult outcomes of PA VSD MAPCA following repair during childhood in our institution

Methods

Review of clinical records for outcome data including life status, NYHA class, employment status, re-intervention in adult life, arrhythmia, pregnancy, exercise capacity and mode of death, where known. We predefined our population into two groups based on their status at transition to adult care, A) complete repair with RV-PA conduit and VSD closed and B) repaired but VSD left open.

Results

188 patients from our series have transitioned to adult services. As many were tertiary referrals (nationally and internationally) the local follow up population was 53 adults (54.7% male), mean age of those alive under follow up is 27.2±6.5 years, with a mean follow up of 25.3±6.1 years. There were 43 in group A and 10 in group B. Mortality in the total population was 18.9% (10/53), group A (16.3%), group B (30.0%), mean age at death 37.5±10.3 years and 29.9±8.4 years, 6/10 deaths were sudden. 22.6% of the whole group had DiGeorge/22q11 microdeletion, with a learning deficit in 32.7% of the cohort, where this could be assessed. Reinterventions included RV-PA conduit change, coil occlusion, pacemaker implantation, ICD implantation and ablation procedures, overall 39.6% underwent reintervention in adult life. Pregnancy occurred in 33.3% of 24 female patients. 50% of individuals were found to have undertaken some form of paid work and of these 11.5% had DiGeorge.

Conclusions

Complex PA VSD MAPCA is associated with good late survival with late attrition including sudden death and heart failure. 22q11 is associated with learning deficit and consequent lack of employment. Non 22q11 have good educational outcomes and there is less observed deficit regarding employment. Successful pregnancy is possible within this population.

Funding Acknowledgement

Type of funding sources: None.

Non-invasive cardiac output monitoring with electrical velocimetry after cardiac surgery in infants

INTRODUCTION

Low cardiac output following cardiac surgery is a major determinant of outcome that may be improved by early detection, yet there are no widely accepted methods for its measurement in young children. We evaluated the feasibility of the routine use of electrical velocimetry, a non-invasive technique providing continuous measurement of cardiac output, in infants in the early postoperative period.

METHODS

With ethical approval and parental consent, infants undergoing cardiac surgery were recruited. The ICON electrical velocimetry monitor was attached on admission to the intensive care unit (ICU) and remained for up to 24h.

RESULTS

A total of 15 infants were recruited, median age 3 months (interquartile range (IQR) 0.5-7.5) and weight 4.8kg (IQR 3.9-7.1), undergoing various operations. Cardiac index had a weak correlation with arterial lactate (r=-0.24, p=0.02) and no correlation with blood pressure, central venous pressure or arteriovenous oxygen difference. Data were recorded for a median of 19h (range 5-24), with lead detachment or movement artefact the most common causes of data loss. There was marked minute-to-minute variability, with 25% of consecutive measurements having >5% variability.

CONCLUSION

Cardiac index measured by electrical velocimetry in infants in the early postoperative period is impaired by frequent data loss and marked intrapatient variability. Our feasibility study suggests that it is unsuitable for use as a routine monitoring tool in the setting of postsurgical ICU care.

Recurrent noisy pneumothorax mimicking pericarditis

Sounds related to the cardiac cycle may have an extra-cardiac origin. We report a case of recurrent noisy pneumothorax producing a loud rub, audible at a distance from the patient and initially diagnosed as pericarditis. The sounds and their mechanisms of production in this condition are also discussed.

Evidence-based guidelines for the use of defibrillation pads

OBJECTIVE

Defibrillation pads are used routinely at both cardiac arrests and cardioversion procedures. There are currently no evidence-based guidelines on how often pads should be replaced, although it has been suggested that they should be changed as often as every three shocks to maintain optimal performance. Previously, we have shown that on exposure to air, pad mass diminishes over time due to evaporation--an effect likely to lead to poorer conduction between skin and paddle. This prospective study was designed to determine if evaporation is accelerated by the passage of a defibrillation current and to formulate evidence-based guidelines for defibrillation pad replacement.

MATERIALS AND METHODS

3M defibrillation pads (2346N) were collected from acute wards and emergency departments in two hospitals in the UK over a 2 month period. The duration of exposure to air, number and energy of shocks, and type of procedure were recorded. When no longer required, pad masses were determined and the loss of pad mass due to evaporation calculated.

RESULTS

26 pairs of pads were collected from 14 cardiac arrests and 12 cardioversions. The total defibrillation energy used ranged from 150 to 5080 J and evaporative drying time from 4 to 38 min. The rate of evaporation from these pads (86.1 mg x min(-1)) was not significantly different from pads previously studied on volunteers in the absence of a defibrillation current (99.4 mg x min(-1)). Of the defibrillation pads exposed to air for less than 30 min, in only one of 49 pads was the loss of mass due to evaporation consistent with a significant increase in transthoracic impedance (TTI). Correspondingly, of two pads used for more than 30 min, both attained a mass consistent with a significant increase in TTI.

CONCLUSIONS

Defibrillation pads can be used for up to 30 min without evaporation causing a clinically significant increase in TTI. The passage of a defibrillation current across pads does not further accelerate water loss.

How often should defibrillation pads be changed?: the effect of evaporative drying

OBJECTIVE

In order to minimise transthoracic impedance (TTI) during defibrillation, water-based pads are used to improve conductivity between metal defibrillation paddles and skin. Subjectively, these pads appear to dry very quickly; an effect that may lead to an increase in TTI due to poorer conduction between paddles and skin. This study was carried out to assess the effect of evaporative drying of defibrillation pads on TTI.

MATERIALS AND METHODS

TTI was measured at 5-10 min intervals in 20 adult male volunteers across 3M defibrillation pads (2346N) placed in the anterior-apical position. Measurements of TTI were made at 30 kHz using a Bodystat MultiScan 5000 monitor at end-expiration. A third pad was placed on the left precordium and its mass recorded each time a TTI measurement was made.

RESULTS

The median age of subjects was 22 years (range 21-52 years) and their median body mass index was 23.1 kg m(-2) (range 18.4-42.8 kg m(-2)). Median room temperature was 23.0 degrees C (range 19.0-24.0 degrees C) and the median humidity was 31.0% (range 28.0-48.0%). 3M defibrillation pads had an initial mean mass of 25.14 g (S.D. +/- 0.41 g). Changes in defibrillation pad mass due to evaporative loss occurred immediately and rapidly, with all measurements being significantly lower than the baseline value. Mean baseline TTI was 63.6 ohms (S.D. +/- 13.7 ohms). After 30 min a statistically significant (P = 0.012) rise of 1.4 ohms (2.2%), was observed corresponding to a 12.6% decrease in pad mass, after which TTI continued to increase in a linear fashion.

CONCLUSION

In the absence of a defibrillation current. 3M defibrillation pads can safely be left on the chest wall for at least 25 min in a typical hospital environment before evaporative drying results in a significant increase in transthoracic impedance.