Cardio investigations

Question 1

Reporting an ECG

Answer 1

Introduce, caliberation, rate, rhythm and axis.

P wave, PR interval, QRS complex, QT Interval, ST segment, T wave and additional waves,

Question 2

ECG - Introduce

Answer 2

Patient name, age, date of ECG and current cardiovascular symptoms and medications.

Question 3

ECG - Caliberation

Answer 3

Say that ‘the paper speed is 25mm/second and the sensitivity is set to 10mm/mV’.

Question 4

ECG - Rate

Answer 4

300 divided by the number of squares per R-R interval or times total number of R waves by 10.

• >100 bpm = sinus tachycardia – anaemia, anxiety, exercise, pain, pyrexia, sepsis, heart failure, hypovolaemia, pregnancy, thyrotoxicosis or sympathomimetics e.g. caffeine or nicotine.
• <60 bpm = sinus bradycardia – physical fitness, vasovagal attack, sick sinus syndrome, acute MI, drugs e.g. β-blockers, digoxin, amiodarone, hypothyroidism or hypothermia.

Question 5

ECG - Rhythm

Answer 5

If cycles are not clearly regular use the ‘card method’ – a sinus rhythm is P followed by QRS.

Question 6

ECG - Axis

Answer 6

The normal axis is between -30° and +90° - look at leads I and aVF and if both are positive the axis is normal but if aVF is negative then need to look at lead II – if positive then the axis is normal.

• Left axis deviation – left anterior hemiblock, inferior MI, VT from LV focus or WPW syndrome.
• Right axis deviation – RVH, PE, anterolateral MI, left posterior hemiblock or WPW syndrome.

Question 7

ECG - P wave

Answer 7

A P wave should precede each QRS and should be <0.12 seconds (<3 small squares).

• Absent P waves – atrial fibrillation, sinoatrial node block or junctional (AV nodal) rhythm.
• Dissociation - between the P waves and QRS complexes suggests complete heart block.
• P mitrale – a bifid P wave caused by left atrial hypertrophy e.g. mitral stenosis.
• P pulmonale – a peaked P wave caused by right atrial hypertrophy e.g. in chronic lung disease.

Question 8

ECG - PR Interval

Answer 8

Start of P to start of QRS and should be 0.12 – 0.2 seconds (3-5 small squares). Prolonged PR suggests delayed conduction in heart block and short PR suggests an accessory pathway e.g. WPW.

• 1st degree heart block – PR interval is prolonged due to a delay in conduction – may be a sign of coronary artery disease, digoxin toxicity, electrolyte disturbance or acute rheumatic carditis.
• 2nd degree heart block – excitation fails to pass through the AV node intermittently:

Mobitz type 1 aka Wenckeback – progressive lengthening of PR then non-conduction.

Mobitz type 2 – PR interval is constant but 1 P wave is not followed by a QRS complex.

2:1 or 3:1 heart block – P wave and QRS is followed by 2 or 3 non-conducted P waves.

• 3rd degree heart block – there is no association between P waves and QRS complexes.

Question 9

ECG - QRS Complex

Answer 9

Normal duration is <0.12 seconds - if prolonged suggests ventricular conduction defect e.g. bundle branch block and if large amplitude suggests ventricular hypertrophy.

The Q wave should be <0.04 seconds in duration and <2mm tall – pathological Q waves may occur within hours of an MI.

Question 10

ECG - QT Interval

Answer 10

Start of QRS to the end of the T wave and varies with rate – prolonged in acute myocardial ischaemia, myocarditis, bradycardia, head injury, hypothermia or electrolyte imbalance.

Question 11

ECG - ST Segment

Answer 11

Should be isoelectric - >1mm elevation in infarctionand >0.5mm depression inischaemia.

Question 12

ECG - T wave

Answer 12

Normally inverted in aVR, V1 and V2, peaked in hyperkalaemia and flattened in hypokalaemia.

Question 13

ECG - Additional Waves

Answer 13

• J waves – seen in hypothermia, subarachnoid haemorrhage and hypercalcaemia.
• U waves – an upward deflection after the T wave and before the next P wave – previous MI.

Question 14

Exercise ECG

Answer 14

A graduated treadmill exercise test with continuous 12 lead ECG and blood pressure monitoring.

Bruce protocol – there are 6, 3 minute stages that range from 1.7 to 5.5 mph and 10-20% graduation.

Question 15

Exercise ECG - Indications

Answer 15

To confirm a suspected diagnosis of ischaemic heart disease, assessment of cardiac function or exercise tolerance, prognosis following MI, evaluation response to treatment (e.g. medication, angioplasty or bypass grafting) or assessment of exercise induced arrhythmias.

Question 16

Exercise ECG - Contraindications

Question 17

Exercise ECG - Difficulties

Answer 17

In some circumstances the test may not be possible:

• Performing – e.g. in patients with osteoarthritis, COPD, stroke or other limitations to exercise.
• Interpreting – e.g. in patients with complete heart block, LBBB, a pacemaker or taking digoxin.

Question 18

Exercise ECG - Stop the Test if . .

Answer 18

Chest pain, dyspnoea, cyanosis, pallor, danger of falling e.g. feeling faint, ST elevation >1mm, atrial or ventricular ectopics, fall in blood pressure >10 mmHg from baseline, failure of BP or HR to rise with effort, SBP >230 or DBP >115 mmHg or 90% maximal heart rate for patients age achieved.

Question 19

Exercise ECG - Interpretation

Answer 19

A positive test can only assess the probability that the patient has IHD – 75% of patients with significant coronary artery disease have a positive test but so do 5% of patients with normal arteries. Down sloping ST depression is much more significant than up sloping ST depression.

Question 20

Ambulatory ECG Monitoring

Answer 20

• With a Holter monitor – continuous ECG monitoring may be used to identify paroxysmal arrhythmias.
• However 70% of patients will not have symptoms during monitoring, 20% will have a normal ECG during symptoms and only 10% will have an arrhythmia coinciding with symptoms.
• As an alternative patients can be given a ‘loop recorder’ that they can activate during an episode.