3 c r a ardiac hythms aNd rrhythmias Case Example: You have just admitted to the nursery Would you be able to determine if this infant needed to a term infant who was delivered by emergency cesarean be kept in the NICU based on his ECG status? section. The obstetrician stated that the infant had expe- Many nurses believe they need to recognize only the rienced intrauterine arrhythmias. The infant’s vital signs life-threatening arrhythmias and the common ones. are stable, he is breathing room air, the chest x-ray is However, as the case just cited exemplifies, it is impor- normal, there is no murmur, and the physical assessment tant that NICU nurses be familiar with nonthreatening examination is normal. The ECG rhythm strip shows a and less common rhythm disturbances so that they can rare beat that is different in appearance from the infant’s make thorough assessments. This chapter classifies cardiac sinus beats. Could you identify the beat? Would you rhythms and arrhythmias by the location of the stimulus. know if it were something to be concerned about? T 16 Cardiac rhythms can be classified as five types: Cardiac arrhythmias can also be classified as bradyar- Sinus: Sinus rhythms originate in the SA node. They rhythmias or tachyarrhythmias. Bradycardia may be may be normal, fast, slow, or irregular. caused by depressed function of the SA node or disor- ders of conduction. Tachycardia may be the result of cel- Atrial: Atrial rhythms originate from somewhere in lular mechanisms such as re-entry or automaticity. This the atria, usually from a focus other than the SA node. book discusses bradycardias and tachycardias under each They indicate an abnormality in atrial conduction. of the pertinent rhythm types. Junctional: Also known as nodal rhythms, junctional rhythms originate from a focus in the AV node. SINUS RHYTHMS Ventricular: Ventricular rhythms originate from a Sinus rhythms are so named because they are electri- focus in the ventricles and indicate a problem with ven- cally stimulated by the sinoatrial (SA) node. The SA node tricular conduction. Any sustained ventricular rhythm is considered to be the heart’s pacemaker. Other areas of can decrease cardiac output, resulting in severely com- the heart have the ability to set the pace when normal promised hemodynamics. pacemaking mechanisms fail. However, in sinus rhythms, Heart blocks: Heart blocks result from an actual the SA node normally sets the pace. blockage to impulse formation or propagation anywhere along the conduction pathway. fl Neonatal ECG Interpretation 3 Cardiac Rhythms and Arrhythmias 16 normAl sInus rhythm Parameters The rhythm normally seen in neonates and infants is ♥♥Normal P, QRS, and T waves called normal sinus rhythm (Figure 3-1). ♥♥Normal PR, QRS, and QT interval measurements ParameTers ♥♥Heart rate less than 90 bpm ♥♥Normal P, QRS, and T waves When reviewing the ECG, look at the RR intervals. In bradycardia, the intervals lengthen (the R waves occur ♥♥Normal PR interval and QRS interval farther and farther apart) as the heart rate becomes ♥♥Heart rate of 90–180 bpm slower and slower (Figure 3-3). Do not rely solely on the ♥♥P wave before every QRS complex digital number on the ECG monitor to diagnose brady- ♥♥PP and RR intervals the same throughout the rhythm cardia. Artifact, such as movement, can give a false strip reading. Always look at the RR intervals and at the ♥♥No pauses patient before initiating treatment. If the patient is pink ♥♥No early beats and breathing, you may wish to monitor the infant’s ability to resume a normal rate. sInus BrAdycArdIA Incidence Brady- refers to a slower than normal rhythm. In Sinus bradycardia is the most frequently observed sinus bradycardia (SB) (Figure 3-2), the rhythm origi- rhythm disturbance in premature infants.9 It may occur nates in the SA node. in up to 90 percent of preterm infants on the first day of T 17 Figure 3-1 fl Normal sinus rhythm. Figure 3-2 fl Sinus bradycardia. Figure 3-3 fl Lengthening of RR interval with slowing heart rate. fl Neonatal ECG Interpretation 3 Cardiac Rhythms and Arrhythmias 17 life.1 It is responsible for up to 35 percent of the arrhyth- Treatment mias in infants.10 Sinus bradycardia may be transient and asymptom- atic. It is important to evaluate the infant’s color and Etiology respiratory status during any bradycardic episode. If the ♥♥Apnea (the most common cause in neonates) infant is symptomatic, stimulate or provide respiratory ♥♥Blood pressure elevation support as indicated. If the slow heart rate persists, begin ♥♥Congenital heart disease resuscitation using Neonatal Resuscitation protocol.11 Treat the cause if the infant is symptomatic or brady- ♥♥Electrolyte imbalances cardia recurs. ♥♥Hypothermia ♥♥Hypothyroidism Complications ♥♥Immaturity of the central nervous system in the pre- Hypotension and decreased cardiac output can result mature infant from sinus bradycardia. If not treated, they can lead to asystole and death. ♥♥Increased vagal tone, such as with spitting, yawning, distended abdomen, or increased intracranial pressure ♥♥Medications sInus tAchycArdIA ♥♥Oversedation Tachy- refers to a faster than normal rhythm. In sinus ♥♥Sinus node disease tachycardia (also called sinus tach or ST), the SA node stimulates conduction at a faster than normal rate ♥♥Vagal stimulation (Figure 3-4). T 18 Parameters ♥♥Hyperthermia ♥♥Normal P, QRS, and T waves ♥♥Hyperthyroidism ♥♥Normal PR, QRS, and QT interval measurements ♥♥Hypovolemia ♥♥Heart rate of 180–230 bpm12 ♥♥Infection ♥♥Pain Incidence ♥♥Sympathetic tone changes, increased demands, or Brief episodes are common in healthy preterm changes in the respiratory cycle may cause the heart infants.12,13 rate to vary Etiology ♥♥Anemia ♥♥Hydrops Figure 3-4 fl Sinus tachycardia. fl Neonatal ECG Interpretation 3 Cardiac Rhythms and Arrhythmias 18 Treatment sInus ArrhythmIA No treatment is indicated if the condition is tran- As the name implies, sinus arrhythmia (Figure 3-5) is sient. Remove or treat the cause. With hydrops, ST can initiated by the SA node. It is a normal variation of be associated with cardiovascular collapse; the infant cardiac rhythm that is associated with respiration. The should be assessed closely and treated as for shock. heart rate increases during inspiration and decreases during expiration. Complications With any tachycardia, the ventricles do not have suf- Parameters ficient time to fill with blood prior to contraction. This ♥♥Normal P, QRS, and T waves may lead to hypotension and decreased cardiac output. ♥♥Normal heart rate ♥♥Slight irregularity of RR interval Figure 3-5 fl Sinus arrhythmia. T 19 Incidence Treatment This arrhythmia is common in the healthy This is a normal variation and does not require newborn.13 It usually occurs at lower heart rates, such as intervention or special monitoring.14 when the infant is resting or sleeping.14 Complications Etiology There are no complications. Sinus arrhythmia is probably the result of intratho- racic pressure changes that occur with respiration. sInus Arrest Sinus arrest (Figure 3-6) occurs when the SA node does not send out an impulse or when the impulse is Figure 3-6 fl Sinus arrest. fl Neonatal ECG Interpretation 3 Cardiac Rhythms and Arrhythmias 19 blocked. After a pause, either the SA node recovers or Etiology another pacemaking area takes over. Sinus node dysfunc- ♥♥Autonomic heart disease associated with sympathetic tion can be further complicated after cardiac surgery and parasympathetic responses with coexistent atrial arrhythmias. This combination is ♥♥Cardiac surgery termed sick sinus syndrome (SSS) or tachy-brady ♥♥Digitalis toxicity syndrome.15–17 ♥♥Hyperkalemia Parameters ♥♥Increased sensitivity to vagal stimulation ♥♥Normal QRS and T waves ♥♥Increased vagal tone ♥♥P waves may change in appearance ♥♥Inflammation of the SA node ♥♥Absent or delayed beat, followed by normal ♥♥Injury to the SA node conduction ♥♥Myopathies ♥♥Heart rate slows during arrest, then may accelerate to normal or tachycardiac arrhythmias Treatment Identify and treat the cause. If bradycardia persists, Incidence the infant may require treatment with epinephrine. Sick sinus syndrome is common after surgery for Isoproterenol has also been used to increase the SA node congenital heart disease, especially if the surgery is near rate but may result in accelerated rhythms.15 Atrial pacing the sinus node.15–18 may be indicated for known SA node injury and can eliminate the need for drug therapy in some infants.10 T 20 Pacing may also alleviate signs of fatigue and improve ATRIAL RHYTHMS hemodynamic status in SSS.19 Atrial rhythms originate in the atria or the SA node. Because the P wave reflects what is happening in the Complications atria, focusing on what is happening with the P wave Escape rhythms may follow sinus arrest and compro- helps the clinician determine if atrial rhythm distur- mise cardiac output. Escape rhythms are nonsinus bances are present. rhythms that occur during or after recovery from another arrhythmia. PremAture AtrIAl contrActIons A premature atrial contraction (PAC) (Figure 3-7) is an early beat that originates in a pacemaker Figure 3-7 fl Premature atrial contractions. fl Neonatal ECG Interpretation 3 Cardiac Rhythms and Arrhythmias 20