This is a very common presentation to paediatric medicine. Cardiac syncope is rare but when syncope occurs on exertion or just after exertion this is suspicious for a primary cardiac cause and warrants careful investigation and discussion even in the presence of a normal ECG.

Certain forms of Long QT for example are most prone to arrhythmia at peak exertion or within five minutes after. This is because the QT interval paradoxically lengthens during recovery. Hypertrophic cardiomyopathy equally is vulnerable to low cardiac output and arrhytmia at higher heart rates on exercise or even mild exertion such as climbing the stairs. Ensure you establish a family history of unusual events including sudden death.

Conversley syncope or pre-syncope (dizziness) is common in relation to postural change or when rising from sleep, especially in teenagers. This is rarely cardiac.

An atypical presentation but one which can be specific for cardiac disease. For us this is in the silver medal position for cardiac specificity.

Consider whether the breathlessness is out of proportion to the exertion. A child who cannot walk up a flight of stairs without stopping is not normal. Cardiac breathlessness is often at lower levels of exercise than you might expect.

This is a common paediatric presentation and does not carry a high specificity in paediatrics. Palpitations are simply awareness of the heart beat. Your role is to establish if these sound like abnormal awareness of normal rhythm (common in anxiety) or normal awareness of an abnormal rhythm. Forceful thudding is often benign whereas rapid fast heart beats with sudden onset 'like a light switch' are more typical of a tachyarrhythmias. Ventricular arrhythmias are thankfully rare outside of those with previous surgery, supraventricular arrhythmias are usually well tolerated and you have time to assess. This is very different if the patient has cardiac instability (collapse or dizziness) with the palpitations. Take a careful history and think about panic attacks as a differential (hyperventilation reduces CO2 and causes dizziness with numbness in extremities).

A very rare symptom of cardiac disease in children, this is more commonly growing pains such as pre-cordial catch or costochondritis. Reassuring features might include sharp, sudden onset and short lived pain with no other associated symptoms. You views on this might change in the context of pleuritic like pain and infection with attention being needed to features of pericarditis.

The pink happy chatty toddler with a soft murmur is in contrast to the teenager with a loud murmur. Remember that flow murmurs are increasingly rare in older children. Be cautious in the youngest children or those approaching secondary school age. This however is an easy one for diagnosis, they just need a scan. Triangulating your other symptoms including subtle tachypnoea or faltering growth together with your ECG can help you work out the priority for that echo (same day, urgent or routine).

On a standard 12 lead ECG, the rhythm strip gives you a ten-second insight. Check each p-qrs complex to confirm sinus rhythm. Sinus rhythm requires an upright P wave of the same shape before every QRS with a normal PR interval.

Check P Wave Regularity: Look along the rhythm strip to see if there is an identical P wave before each QRS? Is the P wave upright in Leads I, II and aVF?

Check P Wave Size: P waves should be small and narrow. That means less than 3 small squares high and less than 2 small squares wide.

Check PR Interval: This represents the time taken for the atria to depolarise so in smaller children with smaller hearts this is naturally shorter. It shortens further at faster rates. It is calculated from the start of the P wave to the start of the QRS. Too short is pre-excitation, too long is heart block. Normally it is about 3 small squares. If it is not check these guideline values

Common Abnormalities

P waves upside down Low atrial rhythm is a normal variant in children. If the sinoatrial node is situated below the normal position then every P wave in Lead II, II and aVF are inverted. Inversion just in Lead III is entirely normal. If only some P waves are upside down then this is an ectopic focus and the patient may be more prone to ectopic tachycardia, refer these.

Narrow QRS without a P wave These are likely supraventricular ectopics. They originate from within the atria but the P wave is typically of a different morphology or not visible hidden in the preceding T wave, sometimes giving a camel-humped appearance. Supraventricular ectopics simply look like QRS complexes without the P wave. All the QRS complexes should however look similar. SVEs are a common variant. You shouldn't have too many (less than 10-20%) and they shouldn't occur in sequence. Don't forget to link with your history.

Wide QRS without a P wave These are likely ventricular ectopics. They arise often from spontaneous depolarisation of the ventricles. This means the ventricles are depolarised directly and not via the fast bundles. This produces a broad QRS complex which looks odd. The abnormal depolarisation also produces discordant repolarisation (ST depression and T wave inversion in leads with a dominant R wave, ST elevation with upright T waves in leads with a dominant S wave) as well as a full compensatory pause (the next R-R interval is double the preceding). As in supraventricular ectopics, unifocal ectopics are easily identified as they are identical, whilst multifocal ectopics have multiple morphologies. Multi-focal VEs warrant a closer look, unifocal VEs are normal in lower percentages around 5-10%.

Slurred QRS without a P wave These are likely junctional ectopics, the half way house of the above. They are far less common than supraventricular or ventricular ectopics. The impulses here arise from the atrioventricular node and are often suppressed by faster impulses originating in the atria. The typical appearance of a junctional ectopic is of a QRS complex with slurring of the upstroke, no obvious p wave and a compensatory pause. These are another normal variant, especially in patients with very low heart rates e.g. eating disorders. A normal echo would help provide reassurance in these cases.

The PR Interval is too short This can be a normal variant but suggests pre-excitation which is a precipitant of SVT. WPW is the extreme version here where the P wave is slow close to a slurred QRS (delta) that they actually touch. A short PR in association with palpitations warrants a review. All WPW (Even if asymptomatic) should be referred.

The PR Interval is too long This is first degree heart block. It is really common at lower heart rates, in healthy children or with high vagal tone. The PR interval is the same for every beat.

The PR Interval is getting longer This is second degree heart block (Mobitz 1, Wenckebach). Again really common at lower heart rates, in healthy children or with high vagal tone. This is frequently seen at night in resting children, in that situation it is rarely sinister.

The PR Interval is normal but some beats are skipped This is second degree heart block (Mobitz 2). It is much less common in children although can again occur with high vagal tone. Worth chatting to a friendly cardiologist about this one.

The P-QRS is totally irregular Third degree or complete heart block represents no conduction through the AV node, and is seen as a complete dissociation between P waves and QRS complexes. If you are not sure then simply using the term AV dissociation makes you look clever and is also true. AV dissociation is never normal and always warrants investigation.

Tall P wave P pulmonane, suggestive of right atrial dilatation.

Prolonged or bifid P wave P waves that are prolonged (wide) or bifid - P mitrale - are suggestive of left atrial dilatation.

Prolonged PR interval is suggestive of first degree heart block. Often this represents a normal variant. However, 1st degree AV block is also seen in myocarditis, drug toxicity, congenital heart disease, hyperkalaemia and ischaemia. A progressive lengthening of the PR interval, before a QRS complex is missed represents Mobitz type 1. It is most commonly seen in sleep and found in ECGs of asymptomatic individuals. While all these patients need further investigation following discussion with a paediatric cardiologist, most will be found to remain in a safe rhythm and require no active treatment.

Calculating and interpreting the rate is a straightforward process and uses information from the rhythm strip. Whilst the rate will likely be automatically calculated on the ECG in front of you, it is always worth double checking, especially in the context of any irregularity.

Check Paper Speed: The standard paper speed for a twelve lead ECG is 25mm/second. In practice, this means that when looking at an ECG one small square represents 40 milliseconds. If it is not standard speed then all the normal calculations below don't apply.

Check Rate: Assuming standard paper speed, count the number of QRS complexes on one ECG and multiply by 6. There are other ways but this is quick and allows for rhythm irregularity.

Compare Rate: Use the table below to check if your rate is normal.

If there is variable or no relationship between P waves and QRS complexes (such as in heart block) then the atrial (count the P waves and multiply by 6) and ventricular (count the QRS complexes and multiply by 6) rates should be calculated separately.

Interpreting the axis is a intimidating. Let's make it easy. Remember the ‘normal’ axis varies with age. The QRS axis is found by comparing the R and S wave in a limb lead. Mostly in paediatrics you should find that in Lead II there is a dominant R wave and only a small or no S wave. Newborns are a bit of an exception.

Look for a limb lead (not a V1-6) where there is almost a pure R wave and no S wave. The axis is exactly in the direction of that lead. Compare it to the picture below.

You can check this with more rules: If there is only an S wave, then it is directly opposite. If the R wave and S wave are equal then it is at 90° to that lead. For nearly all children the normal cardiac axis is down and to the left (in the direction of lead II). Now adapt that principle for the age of your child: Newborn infants - axis is more rightward (almost no S wave in lead III). Young adults - axis is more leftward (mostly positive in lead I and II)

Check the following don't apply:

Superior Axis - Lead I, II and aVF are nearly all negative.

Right Axis - Lead I is negative, lead II is balanced, III is nearly all upward. This is normal in newborns.

Left Axis - Lead I is positive but lead III is heavily negative.

Here is the full list for normal axis values:

QRS amplitude represents the voltage generated on depolarisation of the ventricles. Large voltages occur with more muscle mass and varies with age. Body habitus is also important and in larger children hypertrophy may only be apparent not by complex size but by the relative size of R and S waves. Equally slim children often have large complexes, especially in V3 and V4 which is why we don't use these leads for normal value checks. We recommend you check this every time. It is too easy to miss subtle LVH.

Don't forget all of this assumes you are using normal voltages and not half lead voltage. Normal voltage is 10mm/mv.

Now measure the size of your R and S wave in V1 and V6 and check against the table for that age.

This is a relatively easy assessment. The width represents the speed of conduction in the ventricles from the first to the last myocyte. It should always be less than 120 milliseconds (3 small squares). It actually reduces with age. If you want the average and upper limit of normal these are below. When you find a prolonged QRS then there is abnormal transmission through the conduction bundle delaying depolarisation.

Be aware that in children the shape of the QRS is often not just a simple R then a simple S wave. Changes can occur to give two R waves (RSr) or even two S waves (sRs). We've even seen four RSrs. If you have ever wondered about the letter size then we use little letters to denote a small complex and capitals to indicate a large complex. See the abnormalities section for the variations of these.