2018A02 Describe the cardiovascular changes that occur with morbid obesity.

 

List:

·         Intro

·         Heart

·         Vasculature

·         Haemodynamics

·         Electrics

 

Intro:

Morbid obesity

·     BMI >35kg/m2

Cause of changes

·     ↑Fat mass

·     ↑Lean mass -> ↑Metabolic rate

·     ↑Blood volume

·     Neurohormonal changes (adipokines, SNS)

·     Comorbidities

Summary of effects

·     Decreased reserve

o High LVEDP and near-maximal SV at rest

o Increase in cardiac output mainly by increase in heart rate

o Poor tolerance of exercise, post-op SIRS, excess IV fluid

o Risk of LV failure independent of cardiomyopathy

·     Increased risk of multiple diseases

o Atherosclerosis

o Sleep-disordered breathing

 

Heart:

LV hypertrophy

·     Present in 80%

·     Eccentric: ↑blood volume -> preload

·     Concentric: only if ↑SVR

·     Cause: leptin, angiotensin 2, resistin, SNS

   -> ↓Compliance -> ↑filling pressure

   -> Risk of type 2 AMI

LV dysfunction

·     Multiple types of cardiomyopathy possible:

o Volume-overloaded -> eccentric

o Obesity-induced (fat infiltration, fibrosis)

o Ischaemic (TNFα, IL-6 -> atherosclerosis)

o Hypertensive (angiotensin 2 -> ↑SVR)

RV hypertrophy

·     Present in 30%

·     Cause: PHTN (e.g. sleep-disordered breathing, leptin, angiotensin 2, resistin)

RV dysfunction

·     Causes: sleep-disordered breathing -> cor pulmonale, congestive heart failure

   -> Poorly tolerate ↓PaO2, ↑PaCO2, ↓pH

 

Vasculature:

Hypervolaemia

·     ↑Lean mass -> ↑VO2 -> secondary polycythaemia

·     ↑Angiotensin 2, aldosterone, ↓ANP -> ↑Na+/H2O reabsorption -> ↑ECF and plasma volume

   -> Absolute blood vol ↑

   -> Relative blood vol ↓(approx. 45mL/kg)

Atherosclerosis

·     TNFα, IL-6 -> metabolic syndrome, T2DM -> ↑rate atherosclerosis

   -> ↑risk AMI, stroke peri-op

Hypercoagulability

·     Inflammatory, procoag state: ↑TNFα, IL-6, PAI-1

   -> ↑risk VTE peri-op

   -> ↑risk AMI, stroke peri-op

 

Haemodynamics:

Cardiac output

·     ↔ HR

·     ↑SV and CO

o ↑Lean mass -> ↑VO2

o ↑Blood volume –> ↑preload

o ↑SNS -> ↑contractility

   -> Minimal change cardiac index

   -> ↑MVO2

   -> ↑risk of ischaemia

SVR

Variable:

·     ↓SVR: ↑lean and fat mass -> addition of parallel circuits

·     ↑SVR: angiotensin 2

mAP

Variable

·     ↔: the case in simple obesity

·     ↑: if ↑SVR

PVR

·     Sleep-disordered breathing -> chronic ↓PaO2, ↑PaCO2 -> ↑PVR

   -> Poorly tolerate further ↓PaO2, ↑PaCO2, ↓pH

   -> Risk RV failure

 

ECG:

Simple obesity

Cause: horizontal displacement by visceral fat

·     Low voltage

·     Left axis deviation of P, QRS and T waves

·     Flat T waves inferolaterally

Obesity cardiomyopathy

Cause: fatty infiltration, fibrosis, lipotoxicity

·     Prolonged QT interval

·     AV block

·     Bundle branch block

   -> Risk of AV block including third degree, trifascicular

Common pathology

·     AF: absent P wave, wandering baseline

·     Ischaemia: ST↑↓, TWI, pathological Q waves

·     Cor pulmonale (OSA, OHS): LAD, RBBB, small voltage

 

Feedback welcome at ketaminenightmares@gmail.com