Reduction of diastolic blood pressure: Should hypertension guidelines include a lower threshold target?

Analysis of Energy and Pressure in the Sinus with Different Blood Pressures after Bioprosthetic Aortic Valve Replacement

PURPOSE

To investigate the effect of changing systolic and diastolic blood pressures (SBP and DBP, respectively) on sinus flow and valvular and epicardial coronary flow dynamics after TAVR and SAVR.

METHODS

SAPIEN 3 and Magna valves were deployed in an idealized aortic root model as part of a pulse duplicating left heart flow loop simulator. Different combinations of SBP and DBP were applied to the test setup and the resulting change in total coronary flow from baseline (120/60 mmHg), effective orifice area (EOA), and left ventricular (LV) workload, with each combination, was assessed. In addition, particle image velocimetry was used to assess the Laplacian of pressure (∇ 2 P ) in the sinus, coronary and main flow velocities, the energy dissipation rate (EDR) in the sinus and the LV workload.

RESULTS

This study shows that under an elevated SBP, there is an increase in the total coronary flow, EOA, LV workload, peak velocities downstream of the valve,∇ 2 P , and EDR. With an elevated DBP, there was an increase in the total coronary flow and∇ 2 P . However, EOA and LV workload decreased with an increase in DBP, and EDR increased with a decrease in DBP.

CONCLUSIONS

Blood pressure alters the hemodynamics in the sinus and downstream flow following aortic valve replacement, potentially influencing outcomes in some patients.

Blood pressure goals: A moving target

Clinical guidelines on hypertension have evolved over the past several decades. Each recommends varying blood pressure (BP) cut-offs which define hypertension, determine the thresholds to initiate pharmacotherapy, and guide treatment targets. In addition, different techniques of measuring BP in clinical trials may further contribute to the discrepancies in the achieved BP targets. Physicians find it difficult to navigate through different recommendations for hypertension management based on studies among different age groups and patients with a variety of co-morbidities and target organ involvement. In 2003, JNC 7 recommended a BP goal of < 140/90 mmHg in the general population and < 130/80 mmHg in those with diabetes mellitus or renal disease. JNC 8 re-set the BP target at < 140/90 mmHg for all adults under the age of 60 regardless of co-morbidities, and an even higher target of < 150/90 mmHg for those 60 years or older without diabetes or chronic kidney disease. The more recent results of the Systolic BP Intervention Trial (SPRINT) have a significant influence on the 2017 American College of Cardiology (ACC) and American Heart Association (AHA) guideline which redefines hypertension as BP ≥ 130/80 mmHg. It emphasizes individualized cardiovascular risk assessment and recommends a more aggressive BP target of < 130/80 mmHg and a treatment threshold based on the age, co-morbidities, and cardiovascular risk. The 2017 ACC/AHA guideline also advocates proper BP measurement and provides the estimates of corresponding BP values for clinic, home, and ambulatory BP monitoring measurements. A higher prevalence of hypertension is expected based on the ACC/AHA 2017 guideline. Its implementation may potentially lead to better BP control through enhanced awareness, improved adherence, and more timely initiation and intensification of pharmacologic therapy. Although there is no one-size-fits-all BP target, the ACC/AHA 2017 guideline is simple, inclusive and practical. Nonetheless, more studies are warranted to help further individualize BP goals for elderly patients and those with certain co-morbidities or multiple cardiovascular risk factors.