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Low Heart Rate and Low Blood Pressure after Bariatric Surgery

Patients typically lose a LOT of weight after Gastric Bypass or Gastric Sleeve, and it’s common after massive weight loss for them to trend toward a Heart Rate (HR) or a Blood Pressure (BP) that’s below the typical normal range. Several natural questions come up:

1- How and why do these vital signs often trend below the normal range?
2- Is it OK for the Heart Rate or Blood Pressure to be below normal? (usually, it is OK)
3- In the cases where it is a problem, what should be done?

The Heart adapts to the strain of excess weight (as well as it can)

The story begins with the fact that the Obesity Disease (prior to weight loss) puts tremendous strain on the heart and the

vascular system. The heart’s job is to pump blood to the body, to supply oxygen and many other essential resources. The body tissues need a significant amount of oxygen for maintenance (just sitting still, or sleeping) and the tissues need extra oxygen for activity such as walking or exercise. Obviously, extra fat mass leads to extra oxygen demand, but in addition, researchers have found that the support structures needed for the extra fat mass (extra muscle, extra liver, extra kidney, etc.) are even bigger factors that increase oxygen demand.

The simple act of walking or going up stairs is a much bigger thing for a person who suffers from the Obesity Disease. Much more energy (oxygen) is required to move the greater mass that obesity sufferers carry. This is simple physics, from the equation: Work = Force x Distance.

The upshot is that the heart of a person with the Obesity Disease is always working overtime even when they are asleep, and when they exercise then their heart must work MUCH harder than it would at a normal weight.

The heart adapts to this excessive demand as much as it can, and there are two mechanism the heart can use to pump more blood. The first of these is to increase the Heart Rate (HR), and the second is to increase the amount of blood pumped out with each “stroke” or each heartbeat. Both of these mechanisms are for a healthy heart to handle exercise or other situations of increased blood flow and oxygen demand. However as we all know from our personal experience during exercise, the heart has an upper limit for the amount

of blood it can pump. This means that the heart can only handle a certain amount of continuous high demand.

An image of a guy carrying an elephant

An interesting process happens if the heart is constantly pushed near its maximum output capacity. Initially the heart does actually become stronger and more efficient – we see this phase quite commonly in our pre-operative patients who are in their 20’s and 30’s. At this early stage of the disease process, the patient can have a heart that is more powerful than average, similar to an athlete. This is sometimes called a “runner’s heart.” However, over time the changes that the heart makes to adapt to the increased strain (such as increased HR or thicker heart wall) become counterproductive and the heart actually begins to weaken under the strain. The Obesity Disease also leads to a many-fold increase in the percentage of hypertension (high blood pressure), and this increased pressure that the heart must pump against is an added burden on the overloaded heart. Eventually, the sustained overload is likely to cause lasting heart damage in the form of Congestive Heart Failure.

Understanding that the heart will eventually fail under increased strain should give us all a sense of urgency about getting the weight down to relieve the heart overload. The good news is that if we achieve massive weight loss before heart damage sets in, then that “runner’s heart” that was adapted to the very weight load will find it easy to handle the normal load of the lower weight.

CP exercise

Weight Loss Leads to lower Cardiac Demand and lower Heart Rate

Weight reduction leads to big reductions in the body’s demand for oxygen and other resources. Furthermore, around 70% of people with hypertension before bariatric surgery have resolution of the high blood pressure and this further reduces the stress on the heart.

Assuming the heart was strengthened and not yet damaged by years of excess weight and excess cardiac load, as the weight comes down the heart finds it easy to keep up with the more normal blood flow demands. The heart does not have to work as hard, and it slows down. It is very common for patients after massive weight loss to have a resting HR in the 50’s, and sometimes down into the 40’s.

Most of the time, a low HR is a good thing. As long as the person has a good energy level and is able to sustain moderate exercise, then the low HR is just a sign that the heart is being calm and efficient. This low HR (especially with a low/normal blood pressure, reviewed below) leads to less “wear and tear” on the heart muscle, its valves, and all the blood vessels. Patients who feel well with a low HR typically have a lower risk of heart attack or stroke.

In a few cases, our patients have a low HR and they do not feel well. They have a lack of energy, exercise intolerance, lethargy, or other symptoms of low cardiac function. In these rare cases, the failure of the heart to respond to current blood flow demands is usually caused by some damage that took place during the Obesity phase, and some patients need a cardiac intervention such as a cardiac pacemaker.

Low Blood Pressure – this Blog is not about Dehydration

A low BP in the first 3-4 weeks after bariatric surgery is usually caused by dehydration, because the healthy reduction in BP that happens with massive weight loss usually takes about 3 months or more to show up. Although this blog is not about dehydration, here are a few tips:

  • If you are struggling to drink enough fluid, contact your bariatric team right away.
  • If you can drink fluids OK, then drink a lot of fluid and add some salty fluids such as broth or pickle juice (salt helps keep fluid in your bloodstream).
  • If you are taking prescribed blood pressure meds and your blood pressure is running low (whether it’s dehydration or a healthy correction of blood pressure), talk to your bariatric team or your blood pressure doc about reducing meds.

Gradual Long-term Decrease in Blood Pressure

There seem to be many reasons for the Obesity Disease to cause high blood pressure, and one of these is an excess of fluid retained in the body. This fluid is found throughout the body tissues, and people with the Obesity Disease also have an abnormally high volume of circulating blood. Imagine the blood vessels (the arteries and especially the veins) as the “container” for this enlarged circulating blood volume. The capacity of the blood vessels is enlarged in the Obesity Disease, just as the skin “container” has to enlarge to handle the bigger volume of fatty and structural tissues.

As weight comes down to normal, the circulating blood volume diminishes substantially. This is not bleeding, it is a healthy response to weight normalization. The blood vessels (especially the veins) have some ability to shrink to “fit” the reduced blood volume but the shrinkage is very slow just as the shrinkage of the loose skin is slow. This means that at 6 months after bariatric surgery, our patients usually have a reduced (healthy) circulating blood volume that is running through pipes (the blood vessels) that are a bit oversized for the amount of circulating blood. Since the system is “loose,” blood pressure runs toward the low side.

Similar to the HR discussion above, most of the time a low BP is a good thing. Low HR and low BP mean low stress on the system, with less hardening of the arteries and lower rates of kidney disease as well as lower rates of cardiac disease and stroke as mentioned above. As long as the person feels well and is able to be active, there is no medical problem with having a BP that runs below the typical normal range.

However, in a few rare cases the blood pressure runs low and the patient feels weak, tired, or lightheaded. There are a couple of things that the bariatric team and/or colleague physicians can do, so if this happens you should reach out to your bariatric team.

A Special Situation at about 6 months: Orthostasis and Postural Hypotension

Around 10% of our patients have a transient problem with low BP that shows up around 6 months after their bariatric operation. These folks find that when they go from a low position (lying down, squatting for garden work, or sometimes sitting) to a standing position that they feel lightheaded. Sometimes they describe the sensation as dizziness, or the room closing in, or a feeling like they might “black out.” Most often, they feel fine after a few moments though in a few rare cases our patients have actually fainted unexpectedly. This is a special case of temporary low BP, which can happen in patients who have a normal BP most of the time. I’ve included the fancy medical terms for this condition in the sub-head, in case you’d like to Google more resources.

The underlying mechanism begins with the same mismatch between the reduced/healthy circulating blood volume, and the overly capacious veins (especially in the legs) that have not had a chance to shrink to a smaller appropriate size. When we go from a low position to standing, the action of gravity tends to draw all our blood down into the legs. This effect exists in everyone but the body has compensating mechanisms so it ends up being a small effect when the blood volume is properly matched with the vein “pipes.” However, if the vein “pipes” are oversized in comparison to the amount of circulating blood, then the effect of gravity upon standing can pull a substantial part of the blood volume into the legs where the veins are largest. This is not a loss of blood, it’s just that the excess blood volume in the legs causes a shortage of blood at the level of the heart, so that the heart has less blood it can pump to the brain. When the brain runs short of blood for even a few moments, consciousness becomes dim. For the vast majority of patients, the blood gets back to the heart after a few moments and full blood flow to the brain is soon restored.

This condition always resolves after a few weeks or months, as the veins get time to shrink and “catch up” with the appropriately reduced blood volume. While waiting for it to get better on its own, there are several actions a patient can take to reduce the impact in their own case:

  • More hydration (you probably guessed that, right?)
  • Add salt to everything. Again, salt helps increase circulating blood volume and this situation that’s a good thing.
  • Weird move #1 – when you stand up don’t begin walking. Hold on to something for stability, and do a couple of “tippy-toes.” The tippy-toes will contract the muscles in your calves which serves as pump to push the blood out of the veins in the legs back up to the heart where that blood needs to be.
  • Weird move #2 – at the same time you are holding onto something, do at least one fast big deep breath, pulling air in through your nose. This move creates negative pressure in your chest, which pulls the blood up to your heart where it needs to be.
  • If it’s a really big problem, your bariatric team can get you connected with medical colleagues who can arrange medical compression stockings for your legs. This is kind of an external/artificial way of shrinking the leg veins so the blood cannot “pool” there as much.
  • There are actually meds that raise blood pressure if necessary, though these are rarely used.

So in summary…
1- The Obesity Disease is really bad for the heart in the long run, but it can make the heart stronger temporarily
2- Once the heart is relieved of excess demand caused by excess weight, it naturally slows down and this is almost always a good thing.
3- Once the body is relieved of the multiple factors in the Obesity Disease that push toward high blood pressure, the blood pressure tends to fall toward normal. It’s really common to see the blood pressure trend below normal due to healthy changes in fluid balance. Blood pressure below the typical normal range is also a good thing in the vast majority of cases.