February is National Heart Month in the United States, and today is Valentine’s Day, so it seemed appropriate to me to blog about high blood pressure (HBP), especially now that HBP has been redefined, so that 46 percent of U.S. adults allegedly have it, as compared with about 32 percent under the previous definition.
Hypertension is both a consequence of damage or disease in your arteries, as well as a risk factor for cardiovascular disease. It’s also something you have some control over through lifestyle modifications. Changing your lifestyle is always preferable to taking a drug.
Last February, I blogged extensively about the heart, cardiovascular disease, heart-healthy lifestyle factors, and more. To refresh your memory, consider taking another look at my discussions: on 2/1/17, about atherosclerosis, the plaque buildup in your arteries that causes extensive damage to your cardiovascular system; on 2/8/17, about the use of statin therapy in the absence of hypertension; on 2/15/17 and 2/17/17, about the aging heart; on 2/22/17, about the cardiovascular health consequences of insufficient sleep; and on 2/28/17, about the Mediterranean diet and heart-healthy eating.
“Normal” BP is now 120/80 mm Hg and below
No doubt you’ve read recently that the American College of Cardiology, a non-profit medical society of 52,000 members, and the American Heart Association, a voluntary organization, lowered the threshold of what is considered hypertension in new best-practices guideline they jointly issued for the “Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults.”
The ACC/AHA Task Force on Practice Guidelines defined normal blood pressure as below 120/80 mm Hg and “elevated” blood pressure as 120 to 129 mm Hg systolic with a diastolic pressure below 80 mm Hg. (mm Hg. is millimeters of mercury. See below.)
“Stage 1” hypertension is now defined as 130 to 139 mm Hg systolic or 80 to 89 mm Hg diastolic, and “stage 2” hypertension is 140/90 mm Hg or higher.
The old, long-time definition of hypertension was 140/90 mm Hg or higher. What the ACC/AHA is now calling stage 1 hypertension was previously labeled “prehypertension”—a term meant to alert (shake up) patients and to prompt physicians to provide lifestyle education to help delay their patients’ development of hypertension.
Prehypertension is like prediabetes: You don’t actually have the disease, but you could develop it, if you don’t change your exercise, eating, and other lifestyle (e.g., smoking) habits. I’m not fond of diagnoses that predict diagnoses that patients might eventually have, but might not. They seem like scare-tactics medicine to me, and I like to be treated as an intelligent patient, who can reasonably evaluate risk, not as an uninformed patient who needs to be spooked for her own good.
According to two University of Chicago cardiology experts writing in the Feb. 8, 2018 issue of The New England Journal of Medicine: “By reclassifying people formerly considered to have prehypertension as having hypertension, the guideline creates a new level of disease affecting people previously deemed healthy.”
A cynical person may view this change as a way for a member-society of practicing cardiologists to drum up more business for themselves, rather than as a means to increase medical “intervention” and save lives. I can tell you this much. My father, who was an elite cardiologist, never joined the ACC nor did he ever speak of it. As for the AHA, Dad used to throw stacks of its complimentary journals—intended for doctors’ waiting rooms—in the trash, unread. He considered the AHA for laypeople, not physicians.
Being a person who is contrary and skeptical by nature and by nurture, I’ve been waiting for word from the NEJM about the new guideline. Drs. George Bakris and Matthew Sorrentino of Chicago have provided it.
Cutting to the chase, they conclude: “But while a blood-pressure treatment target of less than 130/80 mm Hg makes sense for high-risk patients, for everyone else it seems more reasonable to continue defining hypertension as a blood pressure of 140/90 mm Hg. or higher.”
Cardiac Primer: How the Heart Works
Before I elucidate what constitutes “high risk” and further explain the new guideline, I’m going to repeat a cardiac primer that I’ve previously published. Please skip to the next section if this is ho-hum for you.
Your heart, which is about the size of a fist, has two sides, designated left and right, from your point of view. Each side has two chambers, an upper chamber called an atrium and a lower chamber called a ventricle. The four chambers are muscles, not arteries, as people commonly misunderstand.
A heartbeat begins with an electrical signal that emanates from the pacemaker cells of the sinoatrial (SA) node, a small mass of cardiac muscle fibers located in the rear of your right atrium. The SA node is the natural pacemaker of the heart. When it is functioning normally, it produces what is known as normal sinus rhythm.
Upon being stimulated by an electrical impulse, the atria (the two upper chambers) fill their respective ventricles with blood, which the ventricles, also activated by electrical impulse, propel outward. The two sides of the heart function independently of each other to pump blood into two different circulatory systems. They are the systemic circulation (left side) and the pulmonary circulation (right side). The heart also has its own circulation, which is served by the two main coronary arteries and their branches.
The larger left heart pumps oxygenated blood out into the body (the system), including the head and brain, through big arteries that gradually decrease in size until they end in microscopic capillaries that are wide enough for only one blood cell to pass. It is in the capillaries that the vital exchange of oxygen, carbon dioxide, nutrients, and waste occurs.
Arterial (i.e. oxygenated) blood capillaries exist in beds with venous capillaries, such that you may think of a single capillary as having an arterial end and a venous end. By the time blood reaches the venous capillaries, it is deoxygenated (lacking oxygen). It flows from the venous capillaries into venules and progressively larger veins until it returns to the right atrium of the heart, thus completing the systemic loop. (Veins have nothing to do with blood pressure.)
The right atrium primes its ventricle with this return venous blood, which is not only lacking oxygen, but now contains carbon dioxide that must be expelled into the air via the lungs. The right ventricle pumps this return blood through the pulmonary trunk, which branches to form the right and left pulmonary arteries that go to their respective lungs. Through the respiratory exchange process, this blood releases carbon dioxide and receives oxygen. Oxygen-enriched blood then flows through the four pulmonary veins—two from each lung—into the heart’s left atrium, thus completing the pulmonary circulatory loop.
Generally speaking, arteries carry blood away from the heart, and veins transport blood back. The pulmonary arteries, which carry deoxygenated blood from the right heart, and the pulmonary veins, which supply the left heart with oxygenated blood, are the exceptions.
To understand a blood-pressure reading, you must understand the “cardiac cycle.” This cycle begins with an electrical signal from the SA and consists of three phases: 1) a first phase of relaxation, when both the atria and ventricles are in what is known as diastole; 2) a second phase when the atria contract to fill the ventricles and ventricular systole starts; and 3) a third phase when ventricular ejection occurs. All of this happens in the span of just one heartbeat, which lasts only 0.85 seconds. (Thus, systole is during contraction; diastole during relaxation.)
Traditionally registered on the mercury column of a sphygmomanometer, a blood-pressure reading consists of the highest (systolic) arterial pressure during a given heart beat, expressed over the lowest (diastolic) pressure, the difference being the pulse pressure. If your blood encounters resistance as it circulates in your arteries—for example, from fatty plaque buildup in arterial walls (read about atherosclerosis, 2/1/17)—your heart will have to work harder to propel it. When your heart pumps harder, pressure increases.
Calculating Cardiovascular Risk
Unlike previous ACC-AHA guidelines, Bakris and Sorrentino explain, the 2017 guideline “emphasizes individualized cardiovascular risk assessment and aggressive management of blood pressure at levels of 140/90 mm Hg or higher in patients with a 10-year risk of cardiovascular events of more than 10%. [My emphasis added.]
“Patients with blood pressures of 130 to 139/80 to 89 mm Hg would still receive nonpharmacologic treatment, unless they had a 10-year risk above 10%; in that case, a single antihypertensive agent is recommended in concert with lifestyle changes [quit smoking; start exercising; eat healthier, etc.]”
I have previously published links to a cardiovascular-risk calculator, such as the following: http://www.cvriskcalculator.com/. In order to calculate your risk, you need to know your total and HDL cholesterol levels and your average blood pressure. (My father never put much stock in risk-calculation formulae in which you fill in the numbers. “That’s not medicine,” he would say.)
Bakris and Sorrentino take issue with the 10% 10-year-risk designation because it is not based on randomized, controlled trials, and, thus, lacks supporting evidence. It also differs from the definition of high risk that was applied in the Systolic Blood Pressure Intervention Trial (SPRINT), a prominent multi-center randomized clinical trial sponsored by the National Heart, Lung, and Blood Institute. There, high-risk patients were defined as having a 10-year risk of cardiovascular events of 15% or higher.
SPRINT enrolled more than 9,000 patients over age 50 who had a blood pressure of 130/90 or higher and at least one cardiovascular risk factor. It released results last year.
An Individualized Approach to Hypertension
Bakris and Sorrentino also take issue with other changes suggested in the guidelines, including the elimination of beta blockers from first-line therapy for patients with primary hypertension and no co-existing conditions that require beta-blocker therapy. Some patients, generally younger patients, they observe, “may have an excellent blood-pressure response with appropriately used beta-blockers.”
Not surprisingly, these practitioners believe an individualized approach to hypertension can “help determine the best choice for first-line therapy.” Although they acknowledge that a “detailed discussion of individualized therapy may be beyond the scope of general guidelines,” such as those propounded by the ACC-AHA, “it’s possible to consider general patient profiles [such as patients who are obese or have diabetes] in recommending more efficient ways to lower blood pressure.”
I quote from their conclusion:
“[I]t is problematic to shift the threshold for hypertension to 130/80 mm Hg. Some people with blood pressures of 130 to 139/80 to 89 mm Hg who are at higher cardiovascular risk may benefit from earlier intervention, but though such a broad-brush approach may be fine from a public health perspective, it could overburden our primary care physician workforce. [Amen to that! PCPs are already burning out and quitting medicine at an alarming rate.]
“Proper blood-pressure measurement is critical but time-consuming. The unintended consequence may be that many people, now labeled as patients with hypertension, receive pharmacologic therapy that’s unlikely to provide benefit given their own absolute risk, and they may therefore experience unnecessary adverse events.” [Not to mention incur more cost for drugs that they don’t need.]
I conclude from Bakris’s and Sorrentino’s review of the new blood-pressure guidelines that if it ain’t broke, don’t fix it. There’s no reason to lower the threshold of hypertension from 140/90 to 130/80, across the board. If you have a 10-year risk of a cardiovascular of 15% or higher, the University of Chicago hypertension experts consider it “prudent” to select 130/80 as your target pressure, rather than 120/80 or 140/90. Intervention, as a matter of medical practice, not public health, should be patient-by-patient.
Happy Heart Day.