Case
Hi, I’m calling from the Children’s Emergency Room and I have a 6-week-old female that is having tachycardia at a rate of 210 beats per minute (bpm). Baby looks OK but is breathing a little fast and appears a bit mottled. The mother reports that she has not been eating all that well over the past 48 hours and has been fussy. She’s only had 3–4 wet diapers over the past 24 hours. There have been some sick contacts at home but not unexpected since we’re in the winter season. I’m thinking about giving a fluid bolus but wanted to check with you first. Thoughts?
What am I thinking?
I am worried. There are several reasons for a 2-month-old to have a heart rate above 200 bpm, and none of them are benign. More concerning is the fact that she is presenting to the emergency room and the mother has noted a change. When a mother notes a change in the behavior of their baby, it is generally a good rule to listen, take heed, and investigate. A baby that has not been eating well suggests a problem and if she has a reduction in wet diapers, this concerns me about two possible problems: firstly, her hydration status and secondly, her cardiac output. Breathing fast and a mottled appearance are also concerning signs. Am I dealing with an infection, an undiagnosed congenital heart disease, or a primary arrhythmia? This is a baby I need to monitor carefully, diagnose efficiently, and probably admit to the hospital.
| Differential diagnosis |
|---|
| Likely |
Sinus tachycardia
|
| Possible |
Sinus tachycardia
Supraventricular tachycardia (persistent junctional reciprocating tachycardia) |
| Rare |
| Ventricular tachycardia Inborn error of metabolism |
History and physical
Key points to gather in the history surrounding the history of present illness include the start of the clinical status change, the time period over which the decline occurred, and associated symptomatology. All of these can help guide immediate steps in management. A sudden change in clinical status is more indicative of an arrhythmia. Symptoms of illness such as fever, nasal congestion, vomiting, watery stools, and sick contacts would be concerning for infection. A gradual decline in feedings with an increase in respiratory rates over several days could point to undiagnosed congenital heart disease, or a relatively slow but incessant arrhythmia (as can happen with ectopic atrial tachycardia or persistent junctional reciprocating tachycardia). Intolerance to feedings, loss in weight, and changes in neurologic status may be suggestive of metabolic disorder.
The physical exam is critical to diagnosis, with attention to the cardiovascular exam. Evaluation for new cardiac murmur and palpation of femoral pulses should be performed in all infants presenting with tachycardia. Infants between newborn through 3 months are particularly at risk for congenital heart disease presentation due to critical changes in normal human physiology occurring in the transition from fetal circulation.
The first transition from fetal circulation is the normal closure of the ductus arteriosus that usually occurs within hours of birth but can persist to close later, particularly in premature infants and those with “ductal dependent” lesions. “Ductal dependent” refers to the requirement of a persistent ductus arteriosus to supply blood to either the pulmonary or systemic circulation. Pulmonary ductal dependent circulation would present with cyanosis as the ductus closes and can be picked up by monitoring of oxygen saturation. Systemic ductal-dependent circulation, the most common condition being a coarctation of the aorta, would present with a discrepancy of blood flow to the upper and lower half of the body. A discrepancy in pulse between the brachial and femoral pulses should clue the examiner to a ductal dependency.
Another expected physiologic change is the normal drop in pulmonary vascular resistance that usually occurs at 6–8 weeks of life. For those infants with moderate-sized ventricular septal defects or persistent patent ductus arteriosus, the drop in pulmonary vascular resistance can lead to more shunting from the systemic to pulmonary circulation. This can present as a new cardiac murmur and increased respiratory rate due to excessive pulmonary blood flow.
Outside of the cardiovascular examination, there are other signs on physical exam to guide the examiner and assess the clinical status of the infant. General appearance and interaction should be assessed. Infants who present as lethargic, disinterest in latching onto a nipple, grunting respiration, or inconsolable with weak cry and lack of tears are signs of extremis. Evaluate the skin for color, temperature, or rashes. Infants with beads of sweat on the forehead noted during feeding is a sign of congenital heart disease. An enlarged liver may be indicative of congestive heart failure or metabolic disease.
Diagnostic testing
Here again, the clinical status of the patient is paramount. If the patient is presenting in extremis, efforts should be focused on immediate diagnosis and emergent management. For any scenario, the establishment of intravenous access is often required. For those infants that suffer from a reentrant supraventricular tachycardia, placement of the IV can lead to a vagal response and termination of the arrhythmia. The diagnosis of the arrhythmia is predicated on an electrocardiogram tracing however this should never delay management. A recorded or printed monitor rhythm strip may suffice during IV placement.
Any concern for congenital heart disease is best evaluated with an echocardiogram. If concerns are raised for ductal dependent lesions, ordering of prostaglandin to be available at bedside may be efficient management while awaiting the results of the echocardiogram. Cardiac function may be depressed in infants who have been in a sustained arrhythmia for greater than 24 h. Function improves and gradually returns to normal with the conversion to sinus rhythm. Chest radiograph may also be helpful to determine cardiac size, pulmonary blood flow, and evaluate for pulmonary infiltrates. Blood gas, lactate, complete blood count, chemistry panel, and blood culture are other diagnostic labs to consider for work-up. For metabolic disease, additional specialty labs may include serum ammonia, serum amino acids, and urine organic acids.
Action plan
The action plan should depend on the clinical status and underlying diagnosis of the patient. For a patient in extremis, support of clinical needs is of utmost importance including circulation, secure airway, and breathing. In the clinical scenario presented, the emergency room provider has asked about administering a fluid bolus that can be helpful to determine if the tachycardia is secondary to hypovolemia (see Fig. 4.1 ). Caution should be exercised in providing fluid challenges to patients with congenital heart disease as it may exacerbate congestive heart failure. It is generally recommended to bolus a smaller amount (5 mL/kg) and monitor how the patient responds before giving additional fluid.
