Fetal premature atrial contractions: natural course, risk factors and adverse outcomes. Bet BB, Eijsbroek FC, van Leeuwen E, Linskens IH, Knobbe I, Clur SA, Pajkrt. Ultrasound Obstet Gynecol. 2023 Nov 29. doi: 10.1002/uog.27546. Online ahead of print. PMID: 38030959
Take home points:
- Among fetal patients referred to a tertiary care practice for PACs, 24% resolved before evaluation
- Adverse events (CHD (congenital heart disease), tachyarrhythmias, antiarrhythmic therapy, or death) occurred in 6.8% of the confirmed patients, and CHD specifically diagnosed in 1.5%
- 3.4% had a tachyarrhythmia pre or postnatally, with 25% of those having signs of cardiac failure and 72% requiring antiarrhythmic therapy
- Risk factors for tachyarrhythmia included PACs with short runs of SVT, blocked PACs, PACs in bigeminy, frequent PACs, signs of cardiac failure, and presence of a foramen ovale aneurysm
Commentary from Dr. Jared Hershenson (Greater Washington DC), section editor of Pediatric Cardiology Journal Watch:
PACs are commonly seen in prenatal life, possibly due to physiologic immaturity of the fetal conduction system or stimulation of the atrial wall from the flap valve of a foramen ovale aneurysm. They are most often benign and resolve during fetal life or soon after birth. However, some cases can be associated with congenital heart disease, and others with tachyarrhythmias that could lead to cardiac failure. A retrospective study of patients from 2007-2022 was done at a single center in Netherlands to determine if their management protocol of fetal PACs had merit. All patients with PACs diagnosed by an outside OB were referred for higher level cardiac fetal echocardiogram and had their heart rate monitored weekly. Outcome measurements included pre and postnatally diagnosed CHD, type of CHD, presence and type of tachyarrhythmia, use of antiarrhythmic therapy, and fetal, neonatal, or infant death. PACs were classified as simple, moderate, frequent, blocked, or runs of SVT (see Table 1). Features of cardiac failure included ascites, cardiomegaly, pericardial effusion, pleural effusion, R>L disproportion of chamber sizes, skin edema, and/or tricuspid regurgitation. The presence of PFO aneurysm was also recorded.
1439 patients were referred, but 24.1% of those patients did not have an arrhythmia on the fetal echo. They were not included in the study but were included in the denominator of adverse outcomes calculations. A few other patients who did not have a fetal echo were also excluded. Of the 939 patients included, Table 2 shows the types of PACs present, with most having simple or moderate. 1.4% had signs of cardiac failure noted at the initial visit. 6.8% had an “adverse outcome” which included presence of CHD, tachyarrhythmias, antiarrhythmic therapy, or death. There were 2 fetal deaths, but neither was associated with the PACs. When including the patients without confirmed arrhythmia at time of initial referral, the overall rate drops to 5%. Tachyarrhythmias occurred in 3.4% of patients (2.5% if including all referrals). Of those patients, 25% showed signs of cardiac failure and 72% required antiarrhythmic therapy.
CHD was suspected in 9 patients (1%) prenatally and 8 were confirmed. Another 6 patients were diagnosed postnatally which was 1.5% of the total cases. Most were not significant (eg. L-SVC or small VSDs that closed). One patient had d-TGA and another had Ebstein’s anomaly. The patient with d-TGA had a false negative initial study.
Risk factors for the development of a tachyarrhythmia are shown in Table 5. Notably, atrial bigeminy, blocked PACs, and runs of SVT showed high odds ratios for development of a tachyarrhythmia.
The natural course of prenatal PACs was mostly resolution during the pregnancy (~89%) or by 1.5 months of life if present after delivery (9.7%).
Overall, this study showed that most fetal PACs self-resolve without complications but that there is a higher incidence of associated CHD than in the general population, and 5-7% of patients will have a tachyarrhythmia. Additionally, risk factors for the development of more concerning tachyarrhythmias were shown. Limitations include a possible referral bias, as many simple PACs may have not been sent for higher level assessment. The reason why blocked PACs alone conferred a higher risk is also unclear and not discussed by the authors. They also included one patient with AV block due to SSA antibodies and one who had LQTS diagnosed postnatally, which represent a different subset of patients and a different natural history. Finally, most of the CHD was benign, making this an insignificant “adverse” event.
