CHAPTER
I 11 I
The child with an abnormal pulse rate or rhythm
INTRODUCTION
Most tachyarrhythmias in children are caused by a re-entrant congenital conduction pathway abnormality but some are secondary to poisoning or metabolic disturbance, follow cardiac surgery or occur in the course of cardiomyopathy. In tachyarrhythmias the rate is fast but the rhythm largely regular.
Most bradyarrhythmias are secondary to hypoxia and shock and are pre-terminal events although a few follow conduction pathway damage during cardiac surgery. The rate is slow and the rhythm usually irregular.
Children with congenital conduction pathway abnormalities will present in one of two ways. If they are able to communicate effectively, i.e the older child, they will present early, usually in good condition, with a perception of palpitations. If they are unable to communicate, i.e the younger child and infants, they will present later with poor feeding or even shock if their parent has not noticed the abnormal heart rate.
Those with other causes of tachyarrhythmias, such as poisoning, may present with additional symptoms, depending on the cause and progress of the underlying problem.
Children with bradyarrhythmias will almost always be in severe and pre-terminal respiratory failure or shock on presentation.
This chapter will provide the student with an approach to the assessment, resuscitation and emergency management of children with abnormal pulse rate or rhythm.
APPROACH TO THE CHILD IN WITH AN
occurring and there is adequate circulation.
If there is no evidence of air movement then chin lift or jaw thrust manoeuvres should be carried out and the airway reassessed. If there continues to be no evidence of air movement then airway patency can be assessed by performing an opening manoeuvre and giving rescue breaths (see Basic Life Support, Chapter 4).
Breathing
Assess the adequacy of breathing.
Monitor oxygen saturation with a pulse oximeter.
Circulation
Assess the adequacy of circulation Cardiovascular status
Heart rate and rhythm
This is the defining observation for this presentation. An abnormal pulse rate is defined as one falling outside the normal range given in Chapter 3. In practice, most serious disease or injury states are associated with a sinus tachycardia. In infants this may be as high as up to 220 bpm and in children up to 180 bpm. Rates over these figures are highly likely to be tachyarrhythmias, but in any case of significant tachycardia, i.e 200 in an infant and 150 in a child, an ECG rhythm strip should be examined and, if in doubt, a full 12-lead ECG performed. Very high rates may be impossible to count manually and the pulse oximeter is often unreliable in this regard. Again a rhythm strip is advised.
An abnormally slow pulse rate is defined as less than 60 beats per minute or a rapidly dropping heart rate associated with poor systemic perfusion. If a bradyarrhythmia is found it will almost always be in a child who clearly requires major resuscitation.
Pulse volume
Examination of central and peripheral pulses may show a poor volume peripherally or, more worryingly, also centrally.
Capillary refill
If there is poor skin perfusion with a rhythm abnormality there may be shock. Slow capillary refill (>2 seconds) after blanching pressure for 5 seconds is evidence of reduced skin perfusion. When testing for capillary refill press on the skin of the sternum or a digit held at the level of the heart. Mottling, pallor, and peripheral cyanosis also indicate poor skin perfusion. All these signs may be difficult to interpret in patients who have just been exposed to cold.
THE CHILD WITH AN ABNORMAL PULSE RATE OR RHYTHM
• Effort of breathing Recession
Respiratory rate Grunting
Accessory muscle use Flare of the alae nasi
• Efficacy of breathing Breath sounds
Chest expansion/abdominal excursion
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Blood pressure
Children’s cardiovascular systems compensate well initially in tachyarrhythmias.
Hypotension is a late and often sudden sign of decompensation and, if not reversed, will be rapidly followed by death.
Serial measurements of blood pressure should be performed frequently.
Effects of circulatory inadequacy on other organs
Acidotic sighing respirations
The acidosis produced by poor tissue perfusion leads to rapid deep breathing.
Pale, cyanosed or cold skin
A core/toe temperature difference of more than 2°C is a sign of poor skin perfusion.
Mental status: agitation or depressed conscious level
Early signs of brain hypoperfusion are agitation and confusion, often alternating with drowsiness. Infants may be irritable but drowsy with a weak cry and hypotonia. They may not focus on the parent’s face. These are important early cerebral signs of shock.
Later the child becomes progressively drowsier until consciousness is lost.
Urinary output
Urine flow is decreased or absent in shock. It is not a useful initial assessment but hourly measurement is helpful in monitoring progress. A minimum flow of 1 ml/kg/h in children and 2 ml/kg/h in infants indicates adequate renal perfusion.
NOTE Poor capillary refill, core/toe temperature difference and differential pulse volumes are neither sensitive nor specific indicators of shock when used in isolation.
There are helpful when used in conjunction with the other signs described.
Look for the presence of signs of heart failure
• Tachycardia
• Raised jugular venous pressure
• Lung crepitations on auscultation
• Gallop rhythm
• Enlarged liver
And listen for a heart murmur.
Monitor heart rate/rhythm, blood pressure and core/toe temperature difference.
If heart rate is above 200 in an infant or above 150 in a child or if the rhythm is abnormal perform a standard ECG.
Disability
Assess neurological function.
• A rapid measure of level of consciousness should be recorded using the AVPU scale.
• Pupillary size and reaction should be noted.
• Note the child’s posture: children in shock are usually hypotonic.
• The presence of convulsive movements should be noted.
THE CHILD WITH AN ABNORMAL PULSE RATE OR RHYTHM
Exposure
Take the child’s core and toe temperatures.
Look for evidence of poisoning.
RESUSCITATION
Airway
If the airway is not open, an airway opening manoeuvre should be performed and an airway adjunct placed. Seek urgent anaesthetic help to secure the airway.
Breathing
All children in shock with an abnormal rhythm should receive high flow oxygen through a face mask with a reservoir as soon as the airway has been demonstrated to be adequate.
If the child is hypoventilating or has bradycardia, respiration should be supported with oxygen via a bag-valve-mask device and experienced senior help summoned.
Circulation
If the heart rate is below 60 in a patient with shock, chest compressions should be commenced.
If a child in shock has a narrow complex tachyarrhythmia up to three synchronous electrical shocks at 0·5, 1 and 2J should be given. If the arrhythmia is broad complex give asynchronous shocks. A conscious child should be anaesthetised or sedated first if this can be done in a timely manner. Synchronisation relies on the ability of the defibrillator to recognise the QRST complex, and is designed to avoid shock delivery at a point in the cardiac cycle likely to precipitate ventricular fibrillation.
Ventricular tachycardia in children is usually fast and has no recognisable QRST complexes; in such circumstances it will prove impossible to deliver a shock to the child in synchronous mode, as the defibrillator will fail to “spot” a favourable time for shock delivery. In order to overcome the problem and ensure prompt delivery of effective treatment, non-synchronous shocks are recommended.
The reason this approach is not advocated in stable ventricular tachycardia is that there is more time available to deliver the synchronous shock, because if it takes 30–40 seconds it does not matter.
If the shocked child’s tachyarrhythmia is SVT then he can be treated with intravenous/intraosseous adenosine if this can be administered more quickly than a synchronous electrical shock
Gain intravenous or intraosseous access.
• Take blood for FBC and U&Es, glucose stick test and laboratory test.
• Give a bolus of crystalloid to a patient with bradycardia who is in shock.
While the primary assessment and resuscitation are being carried out a focused history of the child’s health and activity over the previous 24 hours should be gained.
Certain key features which will be identified clinically in the primary assessment, from the focused history, from the initial blood tests and from the rhythm strip and 12-lead ECG can point the clinician to the likeliest working diagnosis for emergency treatment.
From the ECG the arrhythmia can be categorised by the following simple questions:
THE CHILD WITH AN ABNORMAL PULSE RATE OR RHYTHM
THE CHILD WITH AN ABNORMAL PULSE RATE OR RHYTHM
1. Is the rate:
too fast?
too slow?
2. Is the rhythm:
regular?
irregular?
3. Are the QRS complexes:
narrow?
broad?
Bradycardia is most usually a preterminal rhythm. It is usually seen as the final response to profound hypoxia and ischaemia and its presence is ominous. It can also be precipitated by vagal stimulation as occurs in tracheal intubation and suctioning and may be found in post-operative cardiac patients. The rhythm is usually irregular.
In addition bradycardia may be seen in patients with raised intracranial pressure.
These patients will have presented with coma and their management can be found in Chapters 12 and 18.
Bradycardia can be a side effect of poisoning with digoxin or beta-blockers and the management can be found in Chapter 14.
A rapid heart rate with a narrow QRS complex on the ECG is supra-ventricular tachycardia. The rhythm is usually regular.
A rapid heart rate with a wide QRS complex on the ECG is ventricular tachycardia.
Ventricular tachycardia can be provoked by hyperkalaemia and by poisoning with tricyclic antidepressants, with a combination of cisapride and macrolide antibiotics and by terfenadine taken with grapefruit juice. Additional details on the management of the poisoned child with ventricular tachycardia can be found in Chapter 14.