Myocardial function during bradycardia events in preterm infants
Introduction
Transient bradycardia episodes are common in preterm infants and often secondary to apnea. Decreased ventilation with resultant hypoxemia is believed to be the predominant mechanism, although occasionally bradycardia may be found without preceding apnea [1], [2], [3]. The exact mechanism responsible for the bradycardia in this setting is not known, but likely involves inhibition of normal sinus node function by the autonomous nervous system with or without activation of primitive reflexes [4], [5], [6].
Several investigators have studied the cardiovascular effects of bradycardia and found a linear relation between the decrease in heart rate and organ blood flow. Changes in blood pressure were not consistent, and varied with the depth and duration of the bradycardia [7], [8], [9]. All investigators stress that periods of reduced blood flow could negatively affect brain development in preterm infants, and further studies into bradycardia mechanisms and cardiovascular function are warranted.
Point of care ultrasound is used to diagnose and follow cardiovascular status and hemodynamics in preterm infants. Common clinical indications for point of care cardiac ultrasound include hypotension, diagnosis and assessment of a patent ductus arteriosus, sepsis and pulmonary hypertension with associated difficulties in oxygenation [10]. Inadvertently, the operator may capture an abrupt bradycardic event before discarding the images as unsuitable for analysis. New non-Doppler echocardiography techniques such as speckle tracking echocardiography (STE) now make it possible to retrospectively examine myocardial function in further detail [11]. This technique uses computer software to analyse speckles generated by interaction of ultrasonic beam and the myocardium. It is able to track and follow the speckles within the myocardial tissue and borders, and thus produce parameters of myocardial motion, deformation and volume.
The aim of this study is to report on function of the left ventricle (LV) during bradycardia events in preterm infants using speckle tracking analysis.
Section snippets
Study population
Our department receives approximately 1100 admissions per year and serves as a level 4 referral centre for neonatal intensive care. Since 2012, all clinical and research cardiac ultrasound studies are stored on a local server and available for detailed analysis at a later time. The majority of the scans were performed in preterm infants < 30 week gestation.
The database was retrospectively reviewed for studies with apical 4 or 3 chamber views containing bradycardia events, defined as a decrease in
Results
Out of a total of 411 scans in our database, 15 bradycardia events in 14 preterm infants (11 male) were available for further analysis. The median gestational age of the included infants was 26 weeks (range 23 to 29). All were spontaneously breathing infants on nasal continuous positive airway pressure support (n = 14) or nasal cannula oxygen (n = 1), and all were using oral caffeine-base 5 mg/kg/day. Nine infants had a patent ductus arteriosus present (diameter ranging between 0.9 and 2.3 mm).
Discussion
This study presents unique data on myocardial function during bradycardia in preterm infants using a novel technique. During mild to moderate bradycardia in preterm infants, parameters of systolic contractility were maintained and parameters of atrial contractility were reduced. Stroke volume was maintained, presumably by a longer filling time, an increased transmitral pressure gradient and increased base-to-apex wall shortening.
Contractility is a measure of cardiac performance during systole,
Conclusion
In conclusion, we were able to describe LV function in a small sample of preterm infants with mild to moderate bradycardia. Parameters of systolic contractility and stroke volume were maintained and parameters of atrial contractility were reduced with a longer filling time, increased LV filling pressure and increased base-to-apex wall shortening. Bradycardia resulted in reduced total cardiac output, and presumably organ blood flow, with a compensatory increase in cardiac output detected shortly
Conflict of interest statement
None declared.
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