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Sinus Bradycardia after bariatricsurgery

Sinus Bradycardia and Hypotension post Bariatric Surgery

Last Updated: April 25, 2023 | Dr Reza Moazzeni

Introduction

The connection between weight loss and improved health is well-documented, with years of comprehensive research and numerous trials reinforcing this robust correlation. After recognising the transformative effects of shedding pounds, various diets, medical interventions, and surgical procedures have been developed and advocated, which has evolved the weight loss industry into a multi-billion dollar sector. However, weight loss demands substantial mental fortitude and commitment, leading many to struggle. Drastic lifestyle changes are often necessary, prompting numerous individuals to opt for surgical alternatives, such as Gastric Sleeve or Bypass, which have become increasingly popular as shortcuts to bypass these challenges.

Nevertheless, bariatric surgery carries certain short- and long-term risks, like all invasive medical procedures. Some lesser-known complications of weight loss surgery include asymptomatic bradycardia and hypotension (with syncope). This discussion will examine two case studies that highlight these concerns.

Case 1: Sinus Bradycardia

A 48-year-old man with asymptomatic bradycardia was referred for a cardiac evaluation. He visited his General Practitioner, reporting general fatigue and lethargy that had persisted for about six months. The patient had no other symptoms, such as chest pain or dyspnea, and had never experienced syncope or presyncope. Despite his symptoms, he remained physically active and fit.

The patient’s medical history revealed that he had undergone weight reduction surgery approximately 12 months prior to this presentation. Before the surgery, he weighed 106 kg (BMI 35), and at the time of presentation, his weight had dropped to 70 kg (BMI 23). The details surrounding his surgery were unclear, but he mentioned that he had been physically active before the surgery and wanted to lose weight to make exercising easier.

His physical exam showed a low blood pressure of 105/60 mmHg and a low pulse rate of 36 bpm but no other remarkable findings. Blood test results, including hemoglobin, iron, ferritin, vitamin B12, folate, TSH, and renal and liver function, were all within normal ranges. He did not drink alcohol or smoke. An ECG was performed as part of a routine check-up. Bradycardia

Given the marked sinus bradycardia and his father’s history of coronary artery bypass surgery at 60, he had additional cardiac investigations, such as an echocardiogram and a stress test. His heart was structurally normal, and he exhibited excellent exercise tolerance. He could run on a treadmill according to the Bruce protocol for 15 minutes, equivalent to 14.8 METs, without any abnormalities or symptoms. This high level of exercise tolerance is comparable to that of professional athletes.

Case 2: Hypotension and Syncope

A 26-year-old woman, who was 22 weeks pregnant, was referred due to experiencing dizziness and several episodes of syncope at home. Her first syncopal episode occurred when she was eight weeks pregnant, on a warm day, as she stood in the backyard holding a tray. Without any warning signs, she found herself on the ground. Fortunately, her husband was present and quickly helped her to sit up. She recovered rapidly from the incident. The patient had no prior or subsequent cardiac or neurological complaints related to the event.

Following the initial incident, she experienced several episodes of dizziness and presyncope, which occurred when she assumed an upright position, causing her to feel faint. Her symptoms persisted despite multiple visits to the emergency department, three unremarkable Holter Monitors, and a normal echocardiogram. She did not report any chest pain or dyspnea and was not taking any regular medications. She maintained an active lifestyle, going to the gym three times a week and walking 15,000 steps daily. She had been committed to regular exercise even before her pregnancy. ECG post weight loss surgery

She had a notable medical history, including a Gastric Bypass Surgery (Roux-en-Y) performed one year before her current presentation. Before surgery, her weight was 156 kg (BMI 55), which had since decreased to 100 kg (BMI 36). She neither smoked nor had diabetes or hypertension.

During her physical exam, her heart rate was 72 bpm, and her blood pressure measured 103/68 mmHg when lying down and 95/68 mmHg when standing. No other remarkable findings were observed in the exam. Her blood test results, including iron and ferritin, were all within normal ranges. Additionally, her ECG showed no abnormalities.

Discussion:

The examples provided illustrate the complex physiological transformations that occur following bariatric surgery and a rapid, substantial reduction in weight. Numerous studies have demonstrated that Cardiac Output (CO) begins to drop as early as six weeks post-surgery, primarily due to a decline in Heart Rate rather than a change in Systemic Vascular Resistance (SVR).

Leptin

Leptin, a hormone produced by adipose cells, can elevate sympathetic activity and heart rate in individuals with obesity. Leptin levels typically correlate with the amount of fat in the body. As body fat increases, so do leptin levels, signalling the brain to reduce appetite and increase energy expenditure. Leptin levels drop significantly after bariatric surgery.

The two key factors contributing to a slower heart rate after bariatric surgery include diminished oxygen demand and a shift in the sympathovagal balance towards greater parasympathetic control (enhanced vagal tone). Some studies propose that a decline in Leptin levels following surgery could be the primary cause of increased vagal tone. 

Reduced cardiac output can lower blood pressure for all individuals, irrespective of their pre-surgery blood pressure levels. If a person undergoing bariatric surgery already has a lower baseline heart rate and blood pressure, these changes may be more pronounced post-surgery, resulting in more noticeable bradycardia and hypotension.

Case 1

In the first case, the patient had a normal heart rate, blood pressure, and a marginally increased BMI before surgery. Following a weight loss of 36 kg in under six months (33% of body weight), his body’s requirement for stroke volume significantly decreased, which could be accommodated by a heart rate as low as 36. As demonstrated in the image below, his heart rate reached only 133 bpm after 12 minutes of exercise on the Bruce Protocol, indicating a high level of fitness and vagal tone.

Reduced heart rate after weight-loss surgery

Since he is asymptomatic, his bradycardia does not require any particular intervention. The future need for a pacemaker will depend solely on his symptoms rather than just the heart rate. Nonetheless, he requires more frequent follow-up and monitoring due to his initial significant bradycardia.

Case 2

The second case illustrates the combined impact of bariatric surgery and pregnancy on inducing orthostatic hypotension, dizziness, and syncope. The heart rate accelerates throughout pregnancy, and Systemic Vascular Resistance (SVR) decreases due to elevated hormone levels, such as Estrogen, Progesterone, and Relaxin. This decline in SVR leads to the “physiological hypotension of pregnancy,” with systolic measurements potentially dropping as low as 90 mmHg.

The patient became pregnant six months after undergoing Gastric Bypass surgery, having lost more than 56 Kg (35% of body weight), significantly reducing her heart rate and blood pressure. After becoming pregnant, her blood pressure decreased further due to the physiological hormonal changes associated with pregnancy and reduced SVR. Her fainting incident occurred on a warm day, which likely exacerbated the situation through dehydration. Consequently, the cumulative effects of bariatric surgery, pregnancy and likely dehydration led to dizziness, symptomatic orthostatic hypotension, and even syncope.

Management

In the first case, the patient received reassurance and will undergo routine follow-up appointments with their general practitioner. In the second case, the patient was advised to maintain a relaxed approach during pregnancy, ensuring adequate rest and hydration until the pregnancy concludes. Following delivery and the reversal of pregnancy-related hormonal changes, the patient’s blood pressure and symptoms improved, and no specific medical or device therapy was deemed necessary.

The key takeaway from these two cases is the importance of understanding the physiological changes that occur following weight loss surgery, such as bradycardia and hypotension. Thoroughly assessing a patient’s condition and fitness level prior to surgery allows for better judgment regarding post-surgical changes. The distinction between physiological and pathological changes can help prevent unnecessary investigations and alleviate anxiety and stress for patients.

References

  1. Shah, R., Bansal, N.(2014). A woman who lost weight at the cost of her heartbeat. BMJ case reportshttps://doi.org/10.1136/bcr-2014-205359
  2. van Brussel PM,  van den Born BH. Blood pressure reduction after gastric bypass surgery is explained by a decrease in cardiac output. J Appl Physiol (1985). 2017 Feb 1;122(2):223-229. doi: 10.1152/japplphysiol.00362.2016. 
  3. Sanghavi M, Rutherford JD. Cardiovascular physiology of pregnancy. Circulation. 2014 Sep 16;130(12):1003-8
  4. Malik MG, Franklin SM, Whigham LA, Castellanos A, Fontaine JM. Asymptomatic sinus bradycardia following bariatric surgery. Am J Cardiol. 2014 Mar 15;113(6):1049-53

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