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Sinus-Node and Atrioventricular Conduction Disturbances

A physiologic increase in heart rate of 10-20 beats per minute (BPM) occurs during pregnancy (2), and sinus-node dysfunction is rare. Rare cases have been attributed to the supine hypotensive syndrome of pregnancy, caused by uterine compression of the inferior vena cava (IVC) blood return with paradoxical sinus slowing (67). In the rare instance when symptomatic bradycardia occurs, this should be treated with a change in position of the mother (usually a left lateral decubitus position). For persistent symptoms, a temporary pacemaker may be necessary. This can be performed safely, especially if the fetus is beyond 8 wk gestation, after which organogenesis is essentially complete and radiation exposure is of minimal risk.

Although the development of high-degree heart block is not associated with pregnancy, congenital complete heart block in the mother is occasionally first recognized during pregnancy. Congenital complete heart block may become manifest during pregnancy, which may be related to the increased level of medical attention in this period or the altered hemodynamic and autonomic state. Any significant symptoms are often related to the severity of the underlying heart disease. Patients with isolated heart block and no other evidence of conduction system or structural heart disease have a favorable outcome, and supportive pacing during pregnancy is usually not necessary. In contrast, during delivery, temporary pacing is recommended for all women with complete heart block because of the high incidence of syncope and bradycardia resulting from Valsalva (68), and to allow for adequate heart rate response to increased cardiovascular stress.

For patients with symptoms associated with complete heart block or other bradyar-rhythmias during pregnancy, placement of a permanent pacemaker is preferable to prolonged temporary pacing. There are recent reports of permanent pacemaker implantation during pregnancy. Antonelli et al. reported a successful implant of a dual-chamber pacemaker guided by transesophageal echocardiogram (69). Other methods employed to minimize radiation exposure include electrocardiographic and transthoracic echocardiogram guidance (70,71). The issues regarding radiation exposure are similar to those addressed previously, and radiation risk is low after 8 wk gestation.

Syncope During Pregnancy

In most pregnant patients without structural heart disease, syncope is benign, although occasionally it can be a manifestation of a more serious problem. When syncope occurs late in pregnancy while the patient is supine, it is usually caused by impaired venous return to the heart, the result of IVC compression by the gravid uterus, the "supine hypotensive syndrome" (72). Symptoms usually subside when the patient rolls over on her left side, which confirms the diagnosis. Syncope may also occur after standing upright suddenly or after long periods of time, because of a fall in venous return as the result of increased venous pooling associated with pregnancy.

When caval compression or changes in body position cannot explain recurrent syncope, other etiologies must be considered and managed immediately. A complete evaluation of the patient is mandatory, including physical examination, ECG, and laboratory tests. As in nonpregnant patients, multiple potential etiologies must be considered, including tachyarrhythmias, bradyarrhythmias, dehydration, and hypoglyce-mia, among others. In addition, rare causes reported that are specific to pregnant women include abruptio placenta and bleeding caused by ruptured ectopic pregnancy (73,74).

Supraventricular Tachyarrhythmias

Patients with a prior history of SVT should be advised about the possibility of increased symptoms during pregnancy. Sustained SVT should be treated promptly because it can result in impaired fetal blood flow and even fetal demise (75). Adenosine is the drug of choice for acute termination of SVT; the initial dose is 6 mg iv, followed by 12 or even 18 mg, as indicated. For patients who require long-term suppressive therapy, P-adrenergic antagonists should be considered because they have the longest record of safety (with the exception of atenolol, which has been reported to cause decreased birthweight when given early during pregnancy) (40). Digoxin is safe during pregnancy but is less effective; it is probably most useful in combination with P-adrenergic antagonists, achieving better efficacy while minimizing side effects by allowing lower doses of two drugs. Calcium-channel blockers may also be effective, although the potential for fetal bradyarrhythmias has caused some concern with these agents. Procedures that involve fluoroscopic radiation should be avoided, but can generally be performed at low risk after 8 wk gestation. There is a case report of radiofrequency catheter ablation successfully performed during pregnancy in a patient with the WPW and refractory PSVT, using only 70 s of fluoroscopic time and with no complication or evident adverse effects on the fetus (76).

Anticoagulation for AF During Pregnancy

AF during pregnancy in the absence of structural heart disease is rare. It can be seen occasionally in patients with thyrotoxicosis, pulmonary embolism, congenital heart disease, and cardiomyopathy, but it is most common in the setting of rheumatic heart disease (77). Szekely et al. reported AF to be present in 8% of pregnant women with rheumatic heart disease, and systemic thromboembolism was reported in 27% of them (78). Mendelson et al. reported systemic thromboembolism in 23% of pregnant patients with chronic AF and rheumatic mitral-valve disease (79). Since these are high-risk patients for embolic events, despite the lack of adequate prospective studies targeted to this specific population, we believe that they should be fully anticoagulated throughout pregnancy.

Controversies regarding anticoagulation in pregnant women arise mainly from concerns about safety to the mother vs potential damage to the fetus. Coumarin derivatives cross the placenta and can cause an embryopathy, which consists of nasal hypoplasia and/or stippled epiphyses after exposure during the first trimester, and CNS abnormalities after exposure during any trimester (80). Heparin does not cross the placenta and is safe to the fetus, but prolonged heparin use causes osteoporosis; a reduction in bone density is reported in up to one-third of women who receive heparin (81). Low mol-wt heparins (LMWH) also do not cross the placenta and have benefits over unfractionated heparin, such as longer half-life, more predictable dose-response, and a decreased risk of heparin-induced thrombocytopenia (82,83). A recent study showed LMWH to be safe and effective when used in 61 pregnant women at risk of embolic events, although concerns about bone density were raised in this study (83).

Despite the high risk for thrombotic events in women with mechanical valves, considerable controversy exists on the optimal choice of anticoagulation in this high-risk group (84). The controversy arises from the belief that the superior anticoagulation afforded by warfarin outweighs its risk to the fetus; it should be noted that this apparent superiority can be attributed to prior studies using insufficient heparin dosage in high-risk patients (84). Until more studies are available, we suggest that pregnant women with AF at high risk of embolic events (such as rheumatic heart disease) are treated with full-dose heparin, initiated at doses of 17,000-20,000 subcutaneously every 12 h and adjusted to prolong the activated partial thromboplast in time (APTT) into the therapeutic range (see Table 3). Similar therapy is recommended for patients with mechanical valves (82). Based on limited data, LMWH may be a reasonable alternative (82,83).

Ventricular Tachyarrhythmias and Sudden Cardiac Death

Sustained ventricular tachycardia can also occur during pregnancy. Most commonly described is idiopathic VT originating from the right ventricular outflow tract (RVOT) in women with structurally normal hearts. This group of patients may respond to beta-blockers, such as metoprolol. As recently reported by Rashba et al., an increased incidence of adverse cardiac events is observed during the postpartum period in patients

Table 3

Recommendations for Anticoagulation in Patients with AF During Pregnancy

Subcutaneous (SC) heparin initiated in doses of 17,500-20,000 U ql2h and adjusted to prolong a 6-h postinjection APTT into the therapeutic range. LMWHs are probably reasonable substitutes, but more studies are necessary or

Adjusted-dose SC heparin until the 13th wk, warfarin (target INR range 2.5-3.5) until the middle of the third trimester, then adjusted-dose SC heparin until delivery

INR = international normalized ratio; APTT = activated partial thromboplastin time; LMWH = low mol-wt heparin.

(Adapted from: Ginsberg J, Hirsh J. Use of antithrombotic agents during pregnancy. Chest 1998;114: 524S-530S.)

with the long QT syndrome (LQTS) (85). The authors found that therapy with beta-blockers reduced the incidence of cardiac events, and suggested that patients with LQTS who become pregnant should be treated continuously with beta-blockers.

When necessary for immediate termination of VT, direct current (DC) cardioversion has shown to be safe at all stages of pregnancy with no significant ill effects to the mother or fetus (86). Fetal arrhythmias have been reported, so fetal monitoring is advised; however, effects on the fetus are rare, perhaps related to the high mammalian fetal fibrillation threshold, or the fact that the uterus is outside the shocking vector and receives relatively little electrical current. For acute pharmacologic therapy of VT, patients with structurally normal hearts may respond to beta-blockers. If a membrane-stabilizing agent is required, both lidocaine and procainamide have been shown to be relatively safe. For chronic therapy, a beta-blocker is appropriate for the VTs that occur in the setting of a structurally normal heart. When class I or III agents are required, procainamide offers a favorable profile in terms of safety and efficacy.

Therapy with an implantable cardioverter defibrillator (ICD) is a reasonable alternative in patients who have not responded to medical therapy and are at high risk for sudden cardiac death. A recent series reported the experience of 44 women with ICDs in place during pregnancy (87). There was no increase in ICD-related complications or number of ICD discharges during pregnancy, and there were no complications resulting from ICD shocks. Thus, the ICD should be considered an option for women with life-threatening arrhythmias who plan to conceive in the future, since exposure to potentially toxic drugs can be obviated.

The treatment of cardiac arrest during pregnancy (which is fortunately rare, occurring about once in every 30,000 deliveries) was recently reviewed in a statement from the International Liaison Committee on resuscitation (88). In addition to the standard causes, unusual etiologies for arrest should be considered in pregnant women such as amniotic fluid embolism, pulmonary embolism, bleeding, peripartum cardiomyopathy, and aortic dissection. If cardiopulmonary resuscitation (CPR) is necessary, it should be performed as in the nonpregnant state except for modification to avoid compression of the aorta and inferior vena cava (IVC) by the gravid uterus (see Table 4). Thus, it is recommended that CPR be performed either with the patient in the left lateral decubitus position, with a wedge placed under the right flank, or with the uterus displaced manually to

Table 4

Management of Cardiac Arrest in Pregnant Women

Key Interventions To Prevent Arrest

Place the patient in the left lateral position or manually displace uterus Give 100% oxygen Give fluid bolus

Evaluate recently administered drugs

Modifications During Cardiac Arrest

Relieve aortocaval compression by manually displacing gravid uterus, or by using a wedge or position the patient's back on the rescuer's thighs Consider additional etiologies unique to pregnancy, such as amniotic-fluid embolism or pulmonary embolism Involve obstetric and neonatal personnel as early as possible

If all measures are failing and fetal viability exists, consider immediate perimortem cesarean section

(Adapted from: Kloeck W, Cummins RO, Chamberlain D, Bossaert L, Callanan V, Carli P, et al. Special resuscitation situations: an advisory statement from the International Liaison Committee on Resuscitation. Circulation 1997;95:2196-2210.)

the left. The patient should be administered 100% oxygen and fluid boluses, and the recent administration of drugs must be evaluated. Cesarean section should be considered and undertaken promptly (ideally within 5 min of the arrest) if the fetus is viable.

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