CVS Changes with Obesity

Describe the cardiovascular changes that occur with morbid obesity

Obesity is a multisystem disorder defined by an elevated body mass index (BMI):

• Normal: BMI < 25
• Overweight: BMI 25 - 30
• Obese: BMI > 30
• Morbidly Obese:
  • Obesity related disease and a BMI > 35
  • BMI > 40

Characteristics of obesity include:

• Complex genetic and environmental causes
• Increased caloric intake
• Increased metabolic rate (normal for BSA)

The effect of obesity on the cardiovascular system is complex, and can be classified into:

• Hormonal changes
  Abdominal visceral fat is responsible for secreting a large number of hormones which affect cardiovascular parameters:
  • Increased leptin
    Contributes to cardiac remodelling and LVH.
  • Angiotensinogen
    Leads to systemic hypertension and LV remodelling.
    • Small amounts are produced in adipocytes, which increases as fat volume increases
  • Plasminogen activator inhibitor-1
    Reduces fibrinolysis and predisposes to VTE.
  • Inflammatory adipokines
    Impair endothelial function, leading to increased SVR.
  • Catecholamines
    Increased contractility, SVR, and worsen endothelial function.
    • Released with:
      • Hypoxia
      • Hypercapnea
      • Negative intrathoracic pressure
      • Fragmented sleep
        Due to OSA.

• Changes in key cardiovascular parameters
  • Increased VO₂
    Due to increased LBM and fat mass.
  • Increased Blood Volume
    Due to increased angiotensin II and aldosterone.
  • Increased Stroke Volume
    Due to:
    • Increased preload (major factor)
    • Increased contractility (minor factor)
      Due to increased circulating adrenal hormones.
  • Increased Cardiac Output
    To maintain DO₂.
    • Initially with preserved ejection fraction

• Cardiac changes
  • Diastolic dysfunction
    Due to myocardial fibrosis impairing relaxation.
  • Fatty infiltration of myocardium and conducting system
    • Predisposes to arrhythmias
      Risk is worsened by change in myocardial architecture, hypoxia, and increased circulating catecholamines.
  • Biventricular hypertrophy as a response to increased afterload
    • LV afterload increased due to systemic hypertension
      LVH is much more common than RVH.
      • Eccentric hypertrophy due to volume overload
      • Concentric hypertrophy due to pressure overload or hormonal changes
    • RV hypertrophy due to:
      • LV diastolic failure
      • Increased PVR
        • Hypoxia
          Due to:
          • Effects of OSA
          • Increased shunt through collapsed lung bases
        • Acidosis

References

1. Alvarez A, Brodsky J, Lemmens H, Morton J. Morbid Obesity: Peri-operative Management. Cambridge: Cambridge University Press. 2010.
2. Lotia S, Bellamy MC. Anaesthesia and morbid obesity. Contin Educ Anaesth Crit Care Pain 2008; 8 (5): 151-156.