Pregnancy-induced hormonal, haemodynamic and autonomic changes cause an increase in the incidence of both benign arrhythmias and arrhythmias associated with cardiac disease (see Chapter 11, Physiology of pregnancy).
If the abnormal rhythm causes haemodynamic instability, there is potential for fetal compromise.
Problems and special considerations
Sinus tachycardia is normal during pregnancy. Superimposed supraventricular or ventricular ectopic beats occur commonly and may cause palpitations and anxiety. Underlying organic disease is extremely unlikely in healthy women, who should be reassured and advised about avoiding likely precipitators such as caffeine.
Paroxysmal supraventricular tachycardia is more common in pregnancy, and rarely indicates underlying organic disease. Palpitations, dizziness and syncope may occur, and although attacks may terminate spontaneously with rest, persistent tachycardia that does not respond to vagal manoeuvres should be treated acutely with either suitable antiarrhyth- mic agents (adenosine or verapamil) or with DC cardioversion. In refractory cases, His bundle studies and subsequent ablation of abnormal conduction pathways may be indicated, although it is usual to wait until after delivery for such management.
Atrial fibrillation is usually associated with mitral valve disease and less commonly with cardiomyopathy. The major risks from atrial fibrillation in pregnancy are thromboembolic disease and pulmonary oedema. Prophylactic anticoagulants are indicated, and full anticoagulation may be necessary in some situations, such as during and immediately following DC cardioversion. Pregnancy does not alter medical management of atrial fibrillation. It is essential to confirm that therapeutic plasma levels of antiarrhythmic agents are achieved throughout the pregnancy.
Ventricular tachycardia or fibrillation may occur in association with severe organic cardiac disease, such as myocardial infarction. In such potentially life-threatening situations, pregnancy is of secondary concern, and the primary goal of treatment is termination of the arrhythmia by whatever means is effective.
Symptomatic bradyarrhythmias are uncommon in pregnancy. Transient sinus bradycardia may occur in the early postpartum period and does not require treatment in an asymptomatic woman with a structurally normal heart.
Conduction disorders require referral for cardiological opinion, since some cardiologists recommend aggressive management (permanent pacing) of even first-degree heart block during pregnancy, although this is disputed.
Management options
In general, pregnant women with cardiac arrhythmias should be assessed and treated in the same way as those who are not pregnant. Underlying causes such as cardiorespiratory conditions, anaemia, thyrotoxicosis or electrolyte imbalance should not be forgotten, and women should be investigated appropriately. Women with known predisposing cardiac conditions, for example Wolff-Parkinson-White or long QT syndromes, should be referred early for cardiological advice, and plans made both for management during delivery and for the occurrence of an acute arrhythmia.
All commonly used antiarrhythmics cross the placenta (and indeed may be administered to the mother to treat a fetal arrhythmia). Consensus opinion recommends using the lowest effective dose of the most well-established drug. Maternal β-blockade may cause fetal bradycardia and make interpretation of the fetal heart rate trace difficult, and there are reports of fetal growth restriction with their use in pregnant women with heart disease.
DC cardioversion in a pregnant woman requires general anaesthesia and tracheal intubation using rapid-sequence induction. Women in the second half of pregnancy are at risk of aortocaval compression in the supine position, and adequate uterine displacement must be performed to avoid compromise to uteroplacental perfusion. Fetal heart rate monitoring should be instituted before and immediately after the procedure. Prophylactic anticoagulation should be considered during and after DC cardioversion because of the increased risk of thromboembolic disease during pregnancy.
Agents that are associated with increased heart rate (e.g. oxytocin, ephedrine, terbutaline, salbutamol) should be avoided or used very cautiously if needed, in women at risk of tachyarrhythmias.
Cardiac implantable electronic devices in pregnancy
Pregnant women with underlying structural cardiac disease or a significant arrhythmogenic disorder may occasionally present with a cardiac implantable electronic device such as a permanent pacemaker (PPM) or implantable cardioverter defibrillator (ICD) in situ, or may rarely require the insertion of one during pregnancy. These women should be managed by a team that includes an obstetrician, anaesthetist, cardiologist and cardiac electrophysiologist. A well-communicated peripartum management plan should be put in place. Information on the nature of the device, the indication for its insertion, current programmed settings, date of last check and battery status should be elicited. Anaesthetists must be familiar with the mode of operation and the specific characteristics of these devices, particularly their susceptibility to electromagnetic interference.
Electromagnetic waves generated by the use of diathermy, nerve stimulators, magnetic resonance imaging (MRI) or transcutaneous electrical nerve stimulation (TENS) machines and other medical equipment may disrupt the device’s ability to sense an arrhythmia, trigger unwarranted therapy or damage its components. Strategies to minimise these risks include reprogramming the device or the application of a clinical magnet to inactivate the antitachyarrhythmia function of an ICD or revert a PPM to an asynchronous pacing mode; this is typically performed in an operative setting when the use of diathermy is anticipated. The decision to alter device settings must be individualised and should be based on the potential for adverse interactions with electromagnetic interference, taking into account factors such as the distance between the device and the path of electric current (15 cm is the minimum recommended distance), and patient pacemaker dependency. Bipolar diathermy poses a lower risk and should be employed whenever possible. If monopolar diathermy is used, the ground plate should be placed close to the operative site and as far away from the device as possible. Short, intermittent bursts of current at the minimum effective power levels should be used. Equipment for transcutaneous/transvenous pacing or external defibrillation must be readily available in the perioperative period.
Neuraxial blocks for labour analgesia and anaesthesia reduce the adrenergic stimulation associated with pain and anxiety and have been used successfully in this patient group. Continuous maternal heart rate monitoring is advised during labour and delivery, and invasive monitoring should be considered in women with a high-risk profile. If general anaesthesia is required, rocuronium may be preferable to suxamethonium, as the muscle fasciculations associated with use of the latter may trigger shock release by an ICD or cause inhibition of PPM function and have been reported to cause device failure on induction of anaesthesia.
The patient should remain monitored in a high-dependency environment for the initial postpartum period. After delivery, the original programmed settings must be restored and the device checked.
Device implantation during pregnancy is uncommon, but carries the risk of fetal exposure to ionising radiation, which is more hazardous during the period of organogenesis. If there is an urgent clinical need for the insertion of a cardiac electronic device, protective measures such as shielding of the mother’s abdomen and limiting the dose and duration of x-ray screening must be undertaken (pulsed fluoroscopy).
Key points
• No antiarrhythmic drug is considered completely safe for use in pregnancy.
• Older, well-established agents are generally recommended for first-line management, but newer drugs should not be withheld if other means are unsuccessful.
• Relief of aortocaval compression must not be forgotten during an acute arrhythmia.
• Carefully titrated central neuraxial blocks can be used for intrapartum analgesia/ anaesthesia in women with cardiac implantable electronic devices.
• Precautions are required to minimise the effect of electromagnetic interference on device function in the peripartum period.
Further reading
Laksman Z, Harris L, Silversides C. Cardiac arrhythmias during pregnancy: a clinical approach. Fetal Maternal Med Rev 2011; 22: 123-43.
Metz T, Khanna A. Evaluation and management of maternal cardiac arrhythmias. Obstet Gynecol Clin North Am 2016; 43: 729-45.
Salman MM, Kemp HI, Cauldwell MR, Dob DP, Sutton R. Anaesthetic management of pregnant patients with cardiac implantable electronic devices: case reports and review. Int J Obstet Anesth 2018; 33: 57-66.
Stone ME, Salter B, Fischer A. Perioperative management of patients with cardiac implantable electronic devices. Br J Anaesth 2011; 107 (Suppl 1): i16-26.