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

 

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