Tachyarrhythmias and Pregnancy 

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Normal pregnancy is characterised by increased cardiac output, reduced systemic vascular resistance, and a modest decline in mean blood pressure. These changes are associated with a 10–15 bpm increase in HR.
Potential risk factors in pregnancy that can promote arrhythmogenesis include the hyperdynamic state, the altered hormonal milieu, and underlying heart disease. Therapy is justified when there is hemodynamic compromise, which may jeopardise the mother and her fetus due to associated decrease in uterine blood flow

I - Arrythmias, in context

Paroxysmal SVT refers to intermittent pathologic tachycardia that includes atrial fibrillation and flutter, as well as atrial tachycardia. There are no reliable data on the incidence of paroxismal SVT in pregnant women (incidence in the general population is 35 per 100 000 person-years). The main mechanism for the development of SVT is via re-entry (in 60% of cases). Nevertheless, are other mechanisms such as microreentry and focal tachycardias can be at play.
Episodes of SVT occur with increased frequency during pregnancy, particularly in those with underlying congenital or structural heart disease.

The most common supraventricular tachycardia in pregnant women is atrioventricular nodal reentrant tachycardia (1). Atrioventricular nodal reentrant tachycardia usually does not cause any significant problems in healthy pregnant women or their fetus. However, rapid nodal reentrant tachycardia in the presence of heart disease, may produce hemodynamic instability. (2)

Second most common form of supraventricular tachycardia is atrioventricular reentrant tachycardia.
Atrioventricular reentrant tachycardia has been reported during pregnancy in patients with preexcitation syndromes. It is caused by accessory pathways sometimes associated with certain forms of congenital heart disease. It can result in serious hemodynamic deterioration in patients with heart failure due to systolic or diastolic dysfunction, congenital heart disease, or a rapidly conducting antegrade accessory pathway (3).

 Atrial fibrillation rarely occurs in the absence of congenital or valvular heart disease. When it does happen that atrial fibrillation arises in healthy pregnancies, it is usually well tolerated.
However atrial fibrillation is frequently encountered in pregnant women with underlying heart disease or thyrotoxicosis. Drugs such as adenosine, digoxin, propranolol, procainamide and flecainide are relatively secure. Direct cardioversion can be used: there has been no evidence of significant complications.

Sustained ventricular tachycardia (VT) - duration >30 s - is rare in pregnant women. However there are reports that VT, when occurring, originates in the patient with a normal heart, mainly from the right ventricular outflow tract. (4) Idiopathic left VT also occurs in pregnant patients with structurally normal hearts but prognosis is poor when VT is associated with structural heart disease. (5)

II - Diagnosis and Treatment considerations

The pregnant patient with arrhythmias most often seeks medical attention because of palpitations, light-headedness, shortness of breath and/or anxiety. First off, it is important to correctly diagnose the type and mechanism of any underlying arrhythmia to implement the appropriate therapeutic modalitie, examine the existence of organic heart disease and discard causes likely to favor or trigger its. Clues for correct diagnosis and treatment come from findings during physical examination and correct analysis of the electrocardiogram (ECG). Knowing the ECG features of the various types of narrow-QRS or wide-QRS tachycardias are of extreme importance to obtain ECG documentation of the arrhythmia so that the pregnant woman can receive the correct treatment.
In many patients with a narrow-QRS complex tachycardia, the tachycardia rate is very high (180-240 beats/ min) and therefore, after onset of the tachycardia the patient will arrive soon after in an intensive care unit for diagnosis and treatment. If the arrhythmia persists after correction of all factors, treatment should be provided.

Certain drugs may cross the placental barrier, such that careful consideration should be given in selecting the antiarrhythmic drug to prevent adverse effects on the fetus. (7,8) Teratogenic risk is higher during the first eight weeks after fertilization, when organogenesis takes place; after this period, risk is substantially reduced however certain drugs may interfere with growth and fetal development. Choice of the drug will depend not only on the type of arrhythmia, but also whether a single dose or long-term treatment for prevention of recurrence is considered. The use of multiple antiarrhythmic drugs in the treatment of an episode of tachycardia has been associated with fetal bradycardia, so performing fetal rate monitoring is recommended during acute antiarrhythmic therapy.

Additionally, several factors contributing to the difficulty of maintaining therapeutic blood levels during pregnancy are important to keep in mind: (6,9)

1. The increase in intravascular volume can lead to an increased loading dose necessary to achieve therapeutic blood concentrations
2. Reduction of plasma proteins concentration can reduce the fraction of drug bound to them, producing lower total concentration
3. Increased renal blood flow increases associated renal clearance of drugs,
4. Increased hepatic metabolism secondary to the activity progesterone may also increase the clearance of drugs by this route, and
5. Gastrointestinal absorption can be altered by changes in gastric secretion and intestinal motility, which renders the serum concentration of some drugs unpredictable.

The FDA has issued the following categories of antiarrhythmic drugs in pregnancy:
A: Controlled studies showed no risk in the fetus in any trimester of pregnancy.
B: No evidence of risk in humans. The chance of fetal harm is remote, although exists.
C: The risk can not be ruled out. There are no well-controlled clinical studies, and animal studies show risk to the fetus. fetal damage Is likely if the drug is administered during pregnancy, but the potential benefits could exceed the potential risk.
D: Sure evidence of risk. The human studies or information obtained during the investigation or from the demonstrated risk of drug marketing fetal. However, the potential benefits of use of the drug may outweigh the potential risk. For example, the indication may be acceptable in life threatening situations or For serious disease which can not safer drugs administered or these are ineffective.
X: Contraindicated in pregnancy. Studies in animals or humans, or reports during the investigation or subsequent the marketing of the drug showed certain evidence or risk of fetal abnormality, clearly outweighs any benefit to the patient (Table 1).

Table 1 : Pharmacologic treatment within context of pregnancy.

Table summarises the pharmacological treatment (and adverse effects) for the management of SVT in pregnant women.
(-) Drugs not recommended as first election

 Adenosine is the agent most commonly used during pregnancy, with conversion to normal sinus rhythm in over 80% of cases of acute SVT if non-pharmacological manoeuvres have failed, although manoeuvres such as carotid sinus massage and Valsalva maneuver to control SVT are well tolerated during pregnancy.

There are few data on verapamil and diltiazem. Clinical studies (17,18) report no maternal teratogenicity and no side effects during pregnancy. Verapamil has been used in treatment of SVT fetal and management of preeclampsia without adverse effects. However, maternal hypotension, fetal heart block and depression of contractility during treatment of fetal arrhythmias has been also reported. (19) There is also a risk potential for reduction in uterine blood flow. For these reasons, verapamil should best be avoided in acute treatment, particularly if adenosine can be used. The effect of diltiazem is less known, but similar limitations are assumed.

It seems unsafe to judge from the experience of isolated cases however the use of this drug has not been associated with fetal defects nor with adverse hemodynamic nor electrocardiographic effects in the newborn. Although it was proven to cross the placental barrier - particularly in the third quarter of gestation, plasma concentration is low compared to amniotic fluid excretion.

Amiodarone(D-E)

There is limited experience with this drug during pregnancy, but studies report serious adverse effects on the fetus, including hypothyroidism, delayed premature growth. Thus, amiodarone should be reserved only for the treatment of arrhythmias that threaten life and those that are refractory to other drugs (20) Digoxin crosses the placenta freely, and digitalis toxicity in the mother has been associated with fetal death.

III - Special consideration: Wide-QRS tachycardias

Acute treatment 

Differentiation of VT –hemodynamically unstable or stable – is essential. If at any time VT becomes unstable or if there is evidence of fetal compromise, DC countershock (50–100 J) should be delivered immediately. If a DC shock of 50-100 J is unsuccessful, higher energy is mandatory (100–360 J) and without any risk for mother and children.
Acute therapy should start with intravenous procainamide or with ajmaline (50–100 mg iv over 5 min). Procainamide appears to be equally safe. Procainamide is well tolerated and has not been associated with teratotoxicity, whereas the potential risk of ajmaline during pregnancy is unclear and administration should be limited to emergency situations. (5)
Another potential antiarrhythmic drug is lidocaine, which is not known to be teratogenic. Although several studies have shown some adverse effects (increase in myometrial tone, decrease in placental blood flow, fetal bradycardia), its use during the early months of pregnancy is not associated with a significant increase in the incidence of fetal defects. (21)
Class III antiarrhythmic agents (such as sotalol, amiodarone) are very effective drugs in patients with ventricular tachyarrhythmias. During pregnancy, both drugs are of limited value: sotalol appears to be relatively safe, although there is a 3–5% risk of developing polymorphic or torsade de pointes tachycardia. In addition, the ß- adrenergic properties of sotalol must be considered.
Magnesium is another drug with antiarrhythmic properties, particularly in patients with torsade de pointes tachycardia due to QT prolongation. It is known for a long time that in emergency circumstances, magnesium sulfate (dosage 1 to 2 g iv) is effective to treat and to suppress life-threatening ventricular tachyarrhythmias and should be administered over 1 to 2 min. Although this drug is associated with few side effects, maternal hypothermia and fetal bradyarrhythmias have been observed. In a few cases, verapamil is effective in pregnant women with right/left ventricular outflow

IV - Non-Pharmacological Treatment

Electrical cardioversion (up to 400 Joules) 80 has been performed without complications in all stages of pregnancy (22) to treat both supra and ventricular arrhythmias.
To avoid the risk of fetus arrhythmogenesis from the electrical discharge, some authors has suggested that maternal cardioversion should be performed with fetal monitoring, (23) however, no significant effects are expected on the fetus, since the fetuses of mammals have high fibrillation threshold, and the amount of current that reaches the uterus is usually very small. Despite all these reasons and because of the limited information, cardioversion should be performed only when absolutely indicated.

Under certain conditions, in which the episodes of tachycardia are frequent or difficult to control with antiarrhythmic drugs, it is possible to perform a radiofrequency ablation procedure. At present we have the technological means to accomplish this with minimal intervention (24) and even in absence of X-rays (25). (see Figure 1)

Vitamins K antagonists (VKA) may be teratogenic and in many cases should be replaced by unfractionated heparin or low molecular weight heparin during first trimester (26). In a systematic review, administration of warfarin during the entire period gestation produced fetal malformations at 6.4% of cases, but no adverse effects when treatment was changed to heparin between weeks 6 and 12. Warfarin crosses the placenta barrier, and the fetus may receive an overdose even when the mother is in the therapeutic range. Low molecular weight heparin does not cross the placental barrier and has been widely used for treatment and prophylaxis of thromboembolism vein during pregnancy without adverse fetal effects. During the third trimester, frequent laboratory testing is recommended to check that anticoagulation is appropriate (eg., every 10-14 days) and the corresponding dose adjustments, taking into account that some women may be required high doses of VKA and heparin to maintain anticoagulation appropriate. Pregnant women with AF and mechanical valves, should discontinue VKA between 6 and 12 weeks gestation and then, receive a continuous infusion i.v.of unfractionated heparin adjusted-dose or low molecular weight heparin molecular subcutaneous and can start treatment VKA in the second quarter with a only slightly higher teratogenic risk.

Fig 1: 3-D electroanatomic reconstruction with Ensite NavX navigation system of the left ventricle and aortic root.

It shows radiofrequency ablation of left lateral accessory pathway in a pregnant patient. The electrophysiological study and ablation was performed in absence of X-rays.

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