Clinical Biochemistry Aspects of Cardiovascular Disease

Dr Vivion Crowley MRCPath FRCPIConsultant Chemical PathologistBiochemistry DepartmentSt James’s Hospital

Atherosclerosis is a major cause of morbidity and mortality

Clinically manifests as

• Coronary Heart Disease (CHD) angina MI

• Peripheral vascular disease (PVD) Intermittent claudication limb amputation

• Cerebrovascular disease TIA Stroke

Atherosclerotic plaque is the key pathological lesion Underlying the morbidity and mortality associated with atherosclerosis

What are the risk factors for the development of atherosclerotic disease?

ModifiableModifiable Non-Non-modifiablemodifiable

SmokingSmoking AgeAge

*Dyslipidaemia*Dyslipidaemia GenderGender

*Hypertension*Hypertension Family historyFamily history

*Obesity/T2DM*Obesity/T2DM EthnicityEthnicity

Lack of Lack of exerciseexercise

Premature Premature menopausemenopause

Other risk factors for atherosclerosis

•Stress/Personality

•Homocysteine

•Lipoprotein (a)

•Fibrinogen

•Socioeconomic

•Geographic

•? Depressive illness

JBS CVD Risk Assessment Chart - Female

JBS CVD Risk Assessment Chart - Male

European CVD Guideline – SCORE CVD Risk Assessment Charts

How is‘obese’ defined?How is‘obese’ defined?

Body mass index (BMI)= weight/height2 (kg/m2)

Healthy weight

Healthy weight

BMI 20

BMI 25

BMI 30

HealthHazard

HealthHazard

overweightoverweight

Insufficientweight

Insufficientweight

Classification of Obesity & Overweight

0

5

10

15

20

25

1980 1985 1990 1995 1998

Year

USA Germany

UK

Netherlands

data , 1997

Time trends in the prevalence of obesity (BMI > 30kg/m2)

%

WHO MONICA 1997

Central (Visceral) adiposity is associated with a greater risk of developing metabolic syndrome

Criteria for clinical identification of Metabolic syndrome

ComponentComponent Defining valueDefining value

Abdominal obesityAbdominal obesity WC >88cm in femalesWC >88cm in females

>102cm in males>102cm in males

Elevated fasting TriglycerideElevated fasting Triglyceride > 1.65mmol/L> 1.65mmol/L

Reduced HDL cholesterolReduced HDL cholesterol < 1/3mmol/L in females< 1/3mmol/L in females

<1.0mmol/L in males<1.0mmol/L in males

Elevated BPElevated BP SBP ≥ 130mmHg ORSBP ≥ 130mmHg OR

SBP ≥ 85mmHgSBP ≥ 85mmHg

Elevated fasting glucoseElevated fasting glucose 6.0mmol/L6.0mmol/L

Waist circumference is a clinically useful measure of central adiposity

Hypertension

Defined as BP ≥ 140/90

Associated with stroke, CHD, Cardiac Failure, renal failure

Aetiology

- Essential (primary HT) – polygenic disorder

- Secondary HT (consider in younger hyepretensive)

Prevalence

- 33% White males

- 38% Black males

Secondary Hypertension

Renal disease

Renovascular disease (Renal artery stenosis)-Atheroma in older subjects-Fibromuscular dyspalsia in younger subjects

Coarctation of Aorta

Endocrine causes-Primary hyperaldosteronism (Conn’s syndrome)-Cushing’s Syndrome-Phaeochromocytoma

Renal tubular genetic defects-Liddle’s syndrome

Drugs-Streoids-OCP

Dyslipidaemia is a major risk factor for atherosclerosis

Dyslipidaemia refers to any perturbation in lipoprotein metabolism

-Hyperlipidaemia e.g. hypercholesterolaemia

-Hypolipidaemia e.g. hypoalphalipoproteinaemia (low HDL)

The major lipoprotein particles

Very low density lipoprotein (VLDL)VLDL remnant (IDL)Low density lipoprotein (LDL)High density lipoprotein (HDL)

Outline of normal lipoprotein metabolism

LDL accumulates in the atherosclerotic plaque

What is the relationship of plasma lipids and CHD?

The plasma lipid profile consists of

•Total Cholesterol (TC)•HDL Cholesterol (HDLC)•LDL Cholesterol (LDLC)•Triglycerides (TG)•TC:HDLC

Raised TC and LDLC levels are positively associated with CHD

HDLC levels are inversely associated with CHD-High level implies lower risk -Low level implies higher risk (M < 1.0mmol/L, F <1.3mmol/L)

Raised Triglyceride levels are independently associated with CHD

LDL cholesterol is calculated using the Friedewald formula

Treatment targets for Plasma lipids

TC <5.0mmol/LLDLC <3.0mmol/L (primary prevention) <2.5mmol/L (secondary prevention)HDL >1.0mmol/L in males >1.3mmol/L in females

Elevated Plasma Cholesterol levels are associated with increased CHD mortality

Plasma Total Cholesterol levels vary with age and gender

CHD-related mortality is in decline over the last 30 years

WHO Classification of Dyslipidaemia is now outdated

Adopted by WHO in 1970

Based on laboratory parameters

- Lipoprotein analysis - Lipoprotein electrophoresis- Serum/plasma appearance

Most practical classification takes account of aetiology and Plasma Lipid pattern

Primary (Inherited)

Secondary (Acquired)

Secondary Dyslipidaemias have multiple causes

LFTs, U/E, TFTs, BMI, WC, Glycaemic status, medications and dietary habits need to be adequately assessed in the context of dyslipidaemia

Diabetes mellitusObesityAlochol abuseHypothyroidism*Nephrotic syndrome*Chronic Renal failure*Cholestasis*PCOSDrugs-Retinoic acid-Diuretics-Steroids-OCP-HAART-Cyclosporin

* Predominant Hypercholesterolamia

Primary Dyslipidaemia should be considered in specific circumstances

Abnormal lipid profile without obvious secondary cause

Premature CVD

Family hx of Premature CVD

Family hx of dyslipidaemia

Identification of primary dyslipidaemia may have implications1. CHD risk2. Clinical management3. Family screening4. Genetic counselling

Primary dyslipidaemias can be sub-classified

Predominantly elevated plasma cholesterol•Polygenic hypercholesterolaemia•Monogenic hypercholesterolaemias e.g. FH, FDB

Predominantly elevated plasma triglyceride•Lipoprotein lipase (LPL) deficiency•ApoC-II deficiency•Familial hypertriglyceridaemia

Mixed (Combined elevated plasma Cholesterol and Trigs)•Familial combined hyperlipidaemia (FCH)•Dybetalipoproteinamia (Type III HPLA)

Very rare dylipidaemias•Low LDL syndromes e.g. abeta-, hypobeta-lipoproteinaemia

•Low HDL syndromes-ApoA-I mutations-Tangier disease-LCAT deficiency

Miscellaneous – Lp(a), Hyperalphalipoproteinamia

Monogenic Hypercholesterolaemias

All known defective genes causing monogenic hyeprcholesteroloaemiaare involved in the receptor mediated uptake of LDL by LDL Receptor (LDLR)

Familial Hypercholesterolaemia (FH) is the most prevalentautosomal dominant inherited disorder

Caused by mutation in the LDLR (Goldstein and Brown)

High genetic heterogeneity (implications for genetic screening of populations)> 700 mutations

Heterozygous 1 in 500

Homozygous/Compound Het 1 in 1,000,000

Biochemical Characteristics of FH

Pathogenesis•Reduction in functioning LDLR decreases plasma LDL catabolism•Also some degree of LDL overproduction - ? increased IDL conversion or direct liver LDL overproduction

Lipid profile

•Increased plasma Total Cholesterol 8-14mmol/L•Increased plasma LDL Cholesterol 6-11mmol/L•Normal or decreased plasma HDL Cholesterol•Normal plasma triglycerides

Lp(a) – may also be increased ( ? Role in increased CHD risk)

Clinical Characteristics of FH

Tendon Xanthomata are a pathognomic feature of FH-Usual sites are extensor tendons on hands, Achilles tendon, pretibial tuberosity-Present in 70% Heterozgotes by 4th decade of life-Present in Homozygotes by age 5 years -Homozygotes also have cutaneous planar xanthomas e.g. inter-digital spaces, buttocks, knees, hands

Corneal Arcus and Xanthelasmata may also be features of FH

FH is associated with markedly increased risk of CHD and premature death

Heterozygotes

•Mean age of onset of CHD is 43yrs (males) 53yrs (females)•Relative Risk (RR) was 8 pre-introduction of statins for Rx FH•RR in statin era is 3-4

Homozygotes

•Symptomatic CHD may be evident before age 10 years•Usually present by 20 yrs•Mean age of death from CHD is 26 yrs

•Due to atheromatous involvement of the aortic root •Usually present by puberty

•In Heterozygotes, aortic valve involvement is not characteristic

Haemodynamically significant Aortic stenosis is a major cause of morbidity in Homozygous FH

How do you diagnose FH?

Three established sets of diagnostic criteria

1. The Simon Broome FH Register

2. Dutch Lipid Clinic Network

3. US MEDPED Program

Simon Broome Register FH Criteria

Differential diagnosis of FHDifferential diagnosis of FH

• Polygenic HypercholesetrolaemiaPolygenic Hypercholesetrolaemia

• Familial Combined HyperlipidaemiaFamilial Combined Hyperlipidaemia

• Other monogenic Other monogenic HypercholesterolaemiaHypercholesterolaemia

Screening for FHUniversal Population screening – impractical, not cost effective

Screening within the clinical setting (Opportunistic screening)

•Hyperchol, premature CHD, Fam Hx of CHD or dyslipidaemia

Cascade screening of FH relatives

•Use diagnostic criteria (limited sensitivity)

•Genetic approach -52-76% of patient who meet criteria are LDLR Mutation positive

Management of FH

Heterozygotes:

Effective lowering of LDL Chol can significantly reduce morbidity and mortality

Use of high dose Statins is the first line treatment

Statin may not adequately reduce LDL levels

Consider combination with Ezetimibe (18% further reduction), Resin or Fibrate

If lack of response consider LDL-apheresis + statin (rarely required now)

In females consider contraception if commencing statins or other lipid-lowering drugs

Regular non-invasive testing for silent ischemia (every 1-2 years depending on risk)e.g. stress ECGs, thallium scans

Family screening is mandatory in FH

Dysbetalipoproteinaemia •Type III HPLA•Remnant particle disease

Pathophysiology:-Absence of ApoE R mediated removal of chylomicron and VLDL remnants-Mixed HPLA where plasma Cholesterol and Trigs are elevated to the similar levels-Mean untreated levels of P Chol and Trigs is 8-10mmol/L

Clinical features: Palmar xanthomatosis, tubero-euptive xanthomata

Associated with increased risk of premature CHD and PVD (approx 50%)

Excellent repsonse to Fibrates (± statin)

Genetics of Dysbetalipoproteinaemia

There are several different genetically determined isoforms of ApoE

ApoE2/E2 is present in > 90% Type III HPLA

E2/E2 genotype frequency of 1 in 100However Type III HPLA prevalence is 1 in 5000-10000Further environmental “stresses” required to manifest this pheontypee.g. T2DM, alcohol, hypothyroidism, obesityExample of a gene-environment interaction

Other Mutations in ApoE e.g. R147W-can cause an autosomal dominant form of Type III HPLA

CHD – clinical aspects

Spectrum of clinical presentation

Angina

Acute Coronary Syndrome (ACS) Unstable angina MI

Symptoms of ACS-Severe crushing central chest pain-Dyspnoea-Cold sweat-Pallor-Nausea

Diagnosis of Acute Coronary Syndrome (ACS)

Clinical history

ECG -STEMI or NSTEMI-Q waves appear later

Clinical Biochemistry

“Older” Cardiac Biomarkers for Diagnosis of MI

Creatine Kinase (CK)• muscle enzyme• Nonspecific in that it may originate from skeletal or cardiac muscle• start to increase at 3-8h• Peak level 18-24h• Returns to normal 3-4 days

Aspartate transaminase (AST)• Found in Liver and muscle (an dother tissues)• Nonsepcific• Incraese 6-10h• Paek level 24h• Return to normal 3-5 days

Lactate dehydrogenase (LDH)• Nonspecific (LDH 1 isoform is more cardiospecific)• Peak at 72hrs• Return to normal 8-14 days

Changes CK, AST and LDH after MI

New Cardiac Biomarkers for ACS Diagnosis

CK-MB

•Myocardium has higher concentration of CK-MB, more specific for heart•In ACS similar kinetics to total CK•CK-MB >6%of total CK indicates myocradial origin (Fractionated) •CK-MB mass >5

Troponins

•Regulatory complex in muscle consisting of 3 protein T, C, I•Increases in Troponin T or I are very specific for cardiac muscle damage•In ACS increase at 3-6 hr•Peak 18-24 hr•Can remain elevated for 7-10 days •A Troponin T or I taken at 12 hrs post onset of chest pain is very sensitive

Changes in Troponin I or T and CK-MB post MI

Future Markers for use in diagnosis of ACS

Ischaemia modified albumin

- May fulfil a role as an early sensitive marker of ACS

Biochemical changes in Cardiac Failure

Biochemical abnormalityBiochemical abnormality PathophysiologyPathophysiology

HyponatraemiaHyponatraemia Diuretics, increased AVPDiuretics, increased AVP

HypokalaemiaHypokalaemia Diuretics, 2Diuretics, 2oo hyperaldosteronism hyperaldosteronism

Renal FailureRenal Failure Reduced perfusionReduced perfusion

Biomarkers in Diagnosis of Cardiac FailureNatriuretic peptides

•Atrial Natriuretic peptide

•B-type Natriuretic peptide

-Both are normally produced in atrium-Induce natriuresis (Na loss in urine)

BNP - produced in ventricle in cardiac failure

Measurement of BNP or its cleavage product NT-proBNP-Can facilitate the diagnosis of LVF in acute dyspnoeic patient-Also can assist in identifying patinets with early LVF for echocardiogram

How can NT-proBNP be used in clinical practice?