The NICU population is prone to arrhythmias, which may occur as a result of various cardiovascular, systemic, and/or metabolic problems. Arrhythmias in this population are often related to electrolyte imbalances, disturbances in autonomic maturation, central line access, sepsis, pulmonary hypertension, and/or medications. Clinical presentation of these arrhythmias is variable, and depends on the quality, rate, and duration of the arrhythmia. Recognition of these arrhythmic events is often missed due to alarm frequency and fatigue - even when bedside monitors signal, the alarm is often silenced and the neonate presumed to be clinically well unless other metrics support the neonate being unstable or the bedside nurse is concerned about the appearance of the child. Although this study was performed at a 108-bed level IV neonatal ICU, we believe that the breadth and size of our study population makes this data pertinent to all NICUs, regardless of size, acuity, and gestational age dispersion.
Although this is the first prospective study performed in such a detailed, event-by-event manner, previous studies have attempted to retrospectively analyze the prevalence or incidence of neonatal arrhythmias. In a study performed by Bedrawi et al., 12-lead electrocardiograms on were performed on 457 neonates admitted to the NICU and Holter studies were performed on every fourth neonate with a normal electrocardiogram and every neonatal with an abnormal electrocardiogram. Their analysis of 457 electrocardiograms and 139 Holter recordings estimated an incidence of 8.5% for benign arrhythmias and 1.5% for non-benign arrhythmias in the NICU population. They also demonstrated a significant association between neonatal arrhythmias and male gender, older gestational age, lower glucose levels, maternal smoking, high umbilical artery lines, and use of nebulized beta-2 agonists. They noted that of the 100 infants thought to be arrhythmia free on electrocardiogram, nine demonstrated abnormalities on Holter monitoring, thus demonstrating that the sensitivity of electrocardiogram to Holter monitoring was only 89%. This study was also limited by the fact that they did not include neonates less than or equal to three days of life, premature neonates less than or equal to 28 weeks’ gestation, or neonates with multisystem complex congenital anomalies.6
Gender Predisposition
Previous retrospective studies performed to analyze the prevalence or incidence of arrhythmias in the NICU population have found varying results regarding gender predisposition. The majority of studies have shown that male gender is associated with an increased risk of neonatal arrhythmias.2, 5, 6, 8, 9, 10 However, other studies, similar in design, have shown opposite trends. Our results showed that males had a higher prevalence of both benign and non-benign arrhythmias. (Table 5)
Gestational Age Predisposition
Previous retrospective studies performed to analyze the prevalence or incidence of arrhythmias in the NICU population have found varying results regarding age predilection. The majority of studies have shown that being term or near-term is associated with an increased risk of neonatal arrhythmia,2, 5, 6, 8, 9, 10 but other studies have demonstrated disparate trends.1, 5, 11 Our results showed that of the 137 neonates who experienced any arrhythmia, 70% (N = 97) were moderate-to-late preterm and 18% were term, supporting the conclusion that the older gestational age is associated with an increased risk of neonatal arrhythmias. Moderate-to-late preterm neonates demonstrated the highest prevalence of benign arrhythmias, predominantly sinus tachycardia. Extremely preterm and moderate-to-late preterm neonates both had a 3% prevalence of non-benign arrhythmias. (Table 5) The association between gestational age and arrhythmia burden, especially benign arrhythmia burden, may be due to the effect of having a more developed autonomic nervous systems in infants of older gestational ages. Those infants with less developed sympathetic nervous systems may be more prone to bradycardic episodes, whereas those who are older have a more appropriate sympathetic response to pain at stimuli and other disturbances.
Limitations
This was a prospective descriptive study and was not powered to address arrhythmia burden within specific gestational cohorts. Additionally, while daily respiratory support and medication administration was tracked, pertinent laboratory values, such as electrolyte levels and/or hemoglobin levels, which may have an impact on the frequency of both benign and non-benign arrhythmias in the neonatal population, were not obtained at that moment as the arrhythmia may have not been appreciated or not perceived as being clinically relevant. However, through a retrospective chart review, it was noted that none of the neonates with non-benign arrhythmias had abnormal electrolytes on the day of their recorded arrhythmia and only one had a leukocytosis and bandemia, indicating possible infection.
Not all neonates had 12-lead EKGs performed during their study enrollment. This additional data may have helped identify and further specify some of the arrhythmia events including subtle pre-excitation or QT prolongation. Future prospective studies should have routine ECGs performed as part of admission criteria. Furthermore, the bedside nurse was not queried daily to comment whether a non-sustained arrhythmia occurred and if so what type was observed on telemetry. The nursing staff may have seen an arrhythmia, but if they did not document it, it would have been missed.
However, despite these limitations, this study highlights the frequency of arrhythmia in a large neonatal ICU population. To date, no similar prospective study has been performed in this detailed, event-by-event manner.