Systolic shoulder in the uterine artery and augmented 2nd systolic peak in the ophthalmic artery may indicate preeclampsia-associated cardiovascular dysfunction: an explanatory model.

Introduction:

The appearance of a systolic shoulder (S) in the Doppler waveform of the uterine artery (UtA) is an ominous sign in severe preeclampsia (PE). Normal ophthalmic artery (OA) Doppler is characterised by a 2nd systolic peak P2, in addition to the main peak P1 and a relative P2 augmentation is observed in PE (de Oliveira 2013). Both waveform features may indicate maternal cardiovascular dysfunction in severe PE.

Objective:

In physiology the concept of pulse wave (PW) propagation and reflection is well established (Berger 1993). Our main objective is to identify an explanatory model for coherent interpretation of systolic UtA-S and OA-P2 augmentation, and second a brief model validation (Burattini 2014).

Patients and methods:

Modelling process: An model describes coherently how PW reflection and transmission act upon UtA and OA Doppler waveforms. The purpose is to get insight in the appearance of the systolic UtA-S and simultaneous OA P2 augmentation. We consulted key publications on hemodynamics and the manual „McDonald's blood flow in arteries” (Nichols 2011) with regard to hemodynamic changes in severe PE (Melchiorre 2014).

Patients: Since January 2017 we performed OA Doppler in addition to UtA Doppler in patients with severe PE. When a systolic shoulder was present, the time to inflection, T-infl, was assessed in both vessels and the augmentation index for OA flow was calculated: AIx =(P2-ED)/(P2-ED); ED: enddiastole.

Results:

Both Doppler waveform features, systolic UtA-S and systolic OA-P2 augmentation may be explained be PW propagation, with increased reflection and secondary transmission to the periphery and recording sites. Both waveform features start with a contour inflection followed by the UtA-S or OA-P2 respectively, indicating the arrival of the reflected PW at the site of Doppler recording.

In 6 singleton pregnancies with severe PE requiring delivery < 32wks, we found a systolic UtA shoulder. Mean gestational age was 29 ± 3wks and delivery by cesarean section was within 1 week in all patients. Mean T-infl (± SD) was 123 ms (± 9 ms) in the UtA and 141 ms (± 14 ms) in the OA. There was no visual change of the UtA shoulder, but the OA AIx increased considerably in the last week (0.61 to 0.83).

Conclusion:

Maternal condition in severe PE is impaired by cardiac dysfunction (Melchiorre 2014) and increased PW reflection (Khalil 2014). This resembles chronic heart failure, with reduced PW generation but increased peripheral reflection and may be monitored using the AIx (Curtis 2007).

This index inversely relates main systolic peak and increased 2nd systolic peak. Thus the AIx of may favour the diagnostic capacity OA Doppler in cardiovascular dysfunction and has the potential to monitor deterioration of PE.

UtA-S and augmented OA-P2 coincide during systole and are the result of increased PW reflection. The timing is within the range of the temporal resolution and agrees with the arrival time of the reflected PW at the site of Doppler recording.