1. Interpreting blood tests and the ECG: practical risk assessment
Cardiovascular courses
29th October 2008
Interpreting blood tests and the ECG: practical risk assessment
Dr T S Dhanjal PhD MRCP

2. Aims of the talk Understand why we do blood tests.
What to the blood tests mean?
The importance of risk stratification.
The Electrocardiograph (ECG).

3. Why investigate ? To detect the secondary causes of hypertension.
Assess for the consequences of hypertension.
Risk stratification to determine overall cardiovascular risk.
Monitoring of treatment.
Detection of disease association.

4. Detection of secondary hypertension
Serum Potassium
Low
Lowish
Normal
High
3.7 – 4.0
3.7 – 5.2 mEq/l
Hyperaldosteronism
Renal Failure
Primary (Conn’s)
Secondary (RAS)

7. Biochemical Conn’s Serum measurements Potassium Sodium Renin
Aldosterone
Conn’s syndrome
Serum measurements
Secondary hyperaldosteronism
(RAS, renin secreting tumours)
Liquorice
(11b DHD inhibitor)
Liddle’s syndrome

9. Hyperkalaemia May develop in Renal Failure. Drugs ACE I ARBs
Potassium sparing diuretics

10. Serum Sodium High / highish Primary hyperaldosteronism Low / lowish
Secondary hyperaldosteronism (Malignant Hypertension or renal disease)
Diuretic overuse

11. Urea & Creatinine Creatinine
breakdown product of creatine phosphate in muscle.
usually produced at a fairly constant rate by the body.
Filtered by the kidney and not re-absorbed.
If the filtering of the kidney is impaired then blood levels will rise.
Used to determine Creatinine Clearance which estimates the Glomerular Filtration Rate (GFR).

12. Monitoring Creatinine levels
Isolated essential hypertension rarely results in renal impairment.
But concomitant disease (diabetes) or treatment (ACE I / ARB) can exacerbate.
Intrinsic renal disease can cause hypertension.
Serum creatinine only rises with marked damage to nephrons so not a good test to detect early stage kidney disease.
Problem with measuring creatinine clearance is a 24 hour urine collection is required.

13. Is eGFR the answer ?
NSF for renal sevices requires laboratories to estimate GFR using the MDRD formula.
Fundamentally based on serum creatinine measurments so why should it be any better?
Just as sensitive as measuring serum creatinine over time.
BUT variability of eGFR increases as actual GFR improves.

14. Poggio et al 2005

15. Reciprocal creatinine chart

16. Blood Glucose
Type 2 DM increases risk of cardiovascular, renal, retinal and neuropathic complications.
Screen in hypertensive patients:
Random glucose > 11.1 mmol/l.
OGTT.
Is it more important to aggressively control hypertension ?
UKPDS trials

17. Other serum biochemical tests
Uric acid
40% of patients with hypertension.
Increased with alcohol, thiazide diuretics.
Liver function tests
Excess alcohol intake.
Steatohepatitis – diabetes, metabolic syndrome.
Serum calcium
Hypocalcaemia secondary to CRF.
Hypertension associated with 1˚ Hyperparathyroidism.
Hypercalcaemia also associated with thiazide diuretics.

18. 24 hour urine collection
Young, thin patients with paroxysmal symptoms.
Urinary metanephrines.
Metabolite of epinephrine created by action of catechol-O-methyl transferase on epinephrine.
Creatinine Clearance using the Cockroft & Galt formula.
Sodium excretion to quantify salt intake.
Degree of proteinuria - renal biopsy ?

19. Pheochromocytoma

20. Haematology Detection of polycythaemia Raised RBC, Hb & RBC volume.
Primary (PCV) or secondary (hypoxia).
Gaisbok’s syndrome.
Mean Cell Volume
Increased by alcohol and hypothyroidism.
Connective tissue disease
Platelets, ESR, autoimmune antibodies etc.

21. Lipid profile
For assessment of cardiovascular risk.

22. Cardiovascular risk assessment
JBS 2: Joint British Societies' guidelines on prevention of cardiovascular disease in clinical practice, Heart, 2005.
Prepared by: British Cardiac Society, British Hypertension Society, Diabetes UK, HEART UK, Primary Care Cardiovascular Society, The Stroke Association.
The specific objective to reduce the risk of CVD and its complications in high risk patients.
3 categories:
Any form of established atherosclerotic CVD.
Diabetes mellitus (type 1 or 2).
Asymptomatic people without established CVD but who have a combination of risk factors which puts them at high total risk (estimated multifactorial CVD risk 20% over 10 years) of developing atherosclerotic CVD for the first time.
Measure total cholesterol AND HDL

23. Joint British Societies' cardiovascular disease (CVD) risk prediction chart: non-diabetic men.
Prepared by: British Cardiac Society, British Hypertension Society, Diabetes UK, HEART UK, Primary Care Cardiovascular Society, The Stroke Association, Heart 2005;91:v1-v52

24. Assessment of end-organ damage
Kidneys
Urinalysis.
Microvasculature
Retinopathy.
Heart
ECG.
Echocardiography.

25. Left Ventricular Hypertrophy
LVH is one of the earliest manifestations of hypertensive heart disease.
Leads to diastolic dysfunction and heart failure secondary to systolic dysfunction.
Other cardiac complications:
Myocardial Infarction.
Atrial Fibrillation

28. Electrocardiographic assessment of LVH (1)
Sokolow-Lyon index:
There are two criteria with these widely used indices:
* Sum of S wave in V1 and R wave in V5 or V6 >/= 3.5 mV (35 mm)
and/or
* R wave in aVL >/= 1.1 mV (11 mm)
Cornell voltage criteria – These more recent criteria are based upon echocardiographic correlative studies designed to detect a left ventricular mass index >132 g/m2 in men and >109 g/m2 in women.
For men: S in V3 plus R in aVL >2.8 mV (28 mm)
For women: S in V3 + R in aVL >2.0 mV (20 mm)
Cornell voltage-duration measurement
QRS duration×Cornell Voltage > 2440 ms × mV

29. Electrocardiographic assessment of LVH (2)
Sensitivity and specificity for selected ECG criteria of LVH
Criterion
Sensitivity (%)
Specificity (%)
Sokolow Lyon Voltage 22
100
Cornell Voltage Criteria 42 96
Cornell Voltage Duration Criteria 51 95
RaVL > 11 mm 11
Romhilt-Estes > 4 points 54 85
Romhilt-Estes > 5 points 33 94

30. Summary Potassium Diuretics, renal disease, Conn’s. Sodium
Primary hyperaldosteronism.
Creatinine
Monitor renal function.
Glucose
Screen for diabetes mellitus.
Urate
Diuretics, alcohol.
LFTs
Alcohol.
Calcium
Primary hyperparathyroidism
Total Cholesterol / HDL
Calculate cardiovascular risk.
Haemoglobin
Polycythaemia, CRF.
Mean cell volume
Platelets
Connective tissue disease.
Urinalysis
Proteinuria, Haematuria, Glycosuria.
ECG
Left ventricular hypertrophy.