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MONITOR CORNERIRREGULARITIES OF FETAL CARDIAC RHYTHM BY SHARON RECTOR, RNC-OB, C-EFM, MSNCardiac arrhythmia can be simply defined as a variationfrom the normal rhythm of the heart. Fetal arrhythmiasare fairly uncommon occurring in only 1%-3% of allpregnancies (Barnes, 2009). There are three main typesof rhythm disturbances seen in the fetus: irregular heartrhythms, tachyarrhythmias (baseline rate above 180bpm) and bradyarrhythmias (baseline rate below 100bpm). Irregularities of fetal cardiac rhythm are the mostcommon type of fetal arrhythmia and rarely have seriousconsequences, while sustained tachyarrhythmias andbradyarrhythmias can lead to severe complications includingheart failure and hydrops fetalis.IRREGULAR RHYTHMSIrregularities in rhythm seen in the fetus include prematureatrial contractions (PACs), premature ventricular contractions(PVCs) and dropped beats (nonconducted impulses). PACsare the most common fetal arrhythmia and the most commonirregular rhythm. They are usually caused by an ectopicfocus, but they can be exacerbated by maternal ingestion ofcaffeine, decongestant medication (stimulants), or nicotine(Sklansky, 2009). On the electronic fetal monitor (EFM) usingthe external ultrasound transducer, premature contractionsshould be audible as an irregular rhythm and they usuallycause temporary moments of “lift off” or gaps on the tracing.With an internal fetal spiral electrode, PACs will appear asan upward and downward deflection from the baseline. Theupward spike represents the premature atrial contraction,and the downward spike represents the compensatory pause(Barnes, 2009). In most instances the FHR baseline will bevisible between these upward and downward spikes. PACsdo not represent any real risk to the fetus, and they usuallyresolve spontaneously after birth.PVCs are less common than PACs, and they are caused byan ectopic focus in the ventricles that triggers a prematureventricular contraction. PVCs also appear as upward anddownward deflections from the baseline when using theinternal fetal spiral electrode (Barnes, 2009). They too areconsidered benign and usually disappear shortly after birth.Both PACs and PVCs can occur as bigeminy (occurring everysecond beat), trigeminy (occurring every third beat), or atrandom intervals (Barnes, 2009). Dropped beats (or skippedbeats) are the result of nonconducted impulses in the atria,and they appear as downward deflections from the FHRbaseline.TRACING 1VOL. 27 NO. 2 | AUGUST 2013
While irregular rhythms are audible and can be observed onthe internal EFM tracing, they can be diagnosed empiricallyby observing the rhythm with 2D ultrasound imaging.However, to confirm the diagnosis, echocardiography withDoppler flow studies or M-mode analysis can be utilized(Sklansky, 2009). Again, most irregularities in fetal cardiacrhythm are benign, however, they should be documented andreported for evaluation because on rare occasions they mayconvert to a more serious cardiac arrhythmia or be associatedwith a structural cardiac defect.The following EFM tracings are from a 23 y/o, G2P0010admitted at 40 weeks gestation in spontaneous labor.The fetus had previously been diagnosed with a cardiacarrhythmia that was confirmed as PACs via ultrasound andechocardiography.An audible arrhythmia was noted on admission via externalfetal monitoring. The first tracing was obtained with externalEFM – note the multiple areas of lift off. The second tracingwas obtained via internal fetal spiral electrode – note themultiple occurrences of upward and downward deflections.Notice how they are of varying lengths, but yet they canall be placed into one of several groups that appear verysimilar. This suggests that there are multiple ectopic sites.Also note that the baseline FHR (115 bpm) can be identifiedthrough the arrhythmia. Artifact (or loss of signal) can alsoappear as deflections from the baseline, but it will appearextremely inconsistent and in most cases without a visiblebaseline. This fetus was born via spontaneous vaginal deliverywith Apgar scores of 9 and 9 at one and five minutes. A rareirregularity of rhythm was noted via auscultation. The infantreceived routine newborn care and was discharged withoutcomplication. •REFERENCESBarnes, J.D. (2009). Fetal arrhythmias. In A. Lyndon & L.U. Ali (Eds.).Fetal heart monitoring: Principles and practices (4th ed., pp. 267-291). Washington, D.C.: Association of Women’s Health, Obstetric andNeonatal Nurses.Sklansky, M. (2009). Fetal cardiac malformations and arrhythmias. InR.K. Creasy, R. Resnik, J.D. Iams, C. Lockwood, & R.R. Moore (Eds.).Maternal-fetal medicine: Principles and practice (6th ed., pp. 305-345).Philadelphia: W.B. Saunders.ABOUT THE AUTHORSharon Rector is an Education Consultant specializing in perinatalnursing at SSM Health Care in St. Louis.TRACING 2THE PERINATAL TIMES | 7
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