Comprehensive Guide to Tachyarrhythmias: ECG Analysis and Classification

Hi friends, I am Dr. Mayilananthi. In  this session, we are going to discuss   on tachyarrhythmias. So, what is the objective  of this session? At the end of this session,   you will be able to find out the abnormal  rhythm given in an ECG. For example,  

I have given 2 ECGs to analyse the rhythm.  One is given here, the other one is at the   end of the class. So, what is the definition  of tachyarrhythmia? It is self-explaining;   arrhythmia means abnormal rhythm; and tachy means,  the heart rate is more than 100 beats per minute.

We use tachycardia in place of tachyarrhythmias,  but the 2 terminologies are different. We commonly   use tachycardia when there is problem within the  sinus node, there is increased rate in the sinus   node; it may be physiological or pathological.  Whether the this rhythm is normal or abnormal? We  

do not see any P waves. And the QRS complexes,  they are bizarre. Is there any tachycardia or   not? So, we have to calculate the heart rate.  How are we going to calculate the heart rate? 300 divided by number of large boxes between  two R waves. So, how many large boxes  

are there? 1 and 2; 300 divided by 2, the rate  is 150. Yes, this ECG shows tachyarrhythmia.   We are go going to analyse this ECG in a stepwise  manner to find out the rhythm. This image shows   normal impulse formation and conduction.  Tachyarrhythmias can happen if there is  

problem in impulse conduction.  Usually, there will be reentry. There will be circus movement of the  electrical activity around a part of the heart;   for example, around the tricuspid band annulus  in atrial fibrillation. It may also happen  

if there is problem in impulse formation.  For example, if the subsidiary pacemakers,   for like, for example, in the atrium, if it starts  firing at a rate higher than the SA node rate,   you come across tachyarrhythmia. The  commonest cause for tachyarrhythmia  

is reentry. This is the commonest  cause in day to day practice. A simple classification of tachyarrhythmia  is based on the sight of origin of   impulses. It may be ventricular tachyarrhythmia  or supraventricular tachyarrhythmia. We are more  

worried about ventricular tachyarrhythmias,  because they are associated with poorer   prognosis if not recognised and treated early.  Supraventricular tachyarrhythmia are further   classified as atrial tachyarrhythmia or junctional  tachyarrhythmia. In junctional tachyarrhythmia,  

the impulses start from the  AV node or the adjacent area. But the proper way to classify  tachyarrhythmia is based upon the   duration of the QRS complexes. So, what  is the normal duration of the QRS complex?  

It is less than 100 milliseconds. So, if the  QRS duration is less than 120 milliseconds,   we are going to say it is a narrow-complex  tachyarrhythmia. If it is more than 120   milliseconds, you are going to say it is a  wide-complex or broad-complex tachyarrhythmia.  

In narrow-complex tachyarrhythmia, the impulses  start from the atrium or from the AV node and   they activate the ventricles simultaneously with  the resultant normal or near normal QRS duration. In wide-complex tachyarrhythmia, the impulses  may start from the ventricles. The impulses  

will then propagate via the myocytes. It takes  longer time to activate both the ventricles,   with the resultant prolongation of the  QRS complexes. Or, the impulses may start   from the atrium or AV node; then they will  travel via an abnormal His bun His bundle;  

that means, the patient has either RBBB or  LBBB. Or there may be an accessory pathway.   We are going to discuss about  this accessory pathway later. So, whether this ECG shows narrow-complex  tachyarrhythmia or broad-complex tachyarrhythmia;  

let us calculate the QRS duration. In V6,   this is the beginning of the R wave  and this is the end of the S wave.   So, what is the total duration? It almost occupies  a large box. That means, it is 200 milliseconds.  

So, it is an example of wide-complex  tachyarrhythmia. This wide-complex as well as   narrow-complex tachycardia are further classified  based on the regularity of the QRS complexes. If the QRS complexes are going to  occur at regular interval, we are  

going to say it is regular NCT or regular  WCT. If they occur at irregular interval,   we say it is irregular NCT or irregular  WCT. So, whether this one is a regular   wide-complex tachyarrhythmia or  irregular wide-complex tachyarrhythmia?  

So, in rhythm strip, we are going to assess  the distance between the QRS complexes. So,   they occur at regular interval. So, this  is a regular wide-complex tachyarrhythmia. First we are going to discuss on  narrow-complex tachyarrhythmia.  

We have already subclassified this  narrow-complex tachyarrhythmia into 2 types,   regular and irregular. Let us discuss on regular  narrow-complex tachycardia. So, what are the   causes? Sinus tachycardia is the commonest  cause for regular narrow-complex tachycardia.  

It may be physiological or pathological.  It has been dealt already. The second cause   being junctional tachycardia, where the impulses  starts from the AV node or the adjoining area. This has been already discussed earlier.  So, what are the other causes for regular  

narrow-complex tachycardia? AV nodal reentry  tachycardia, atrioventricular reentry tachycardia,   atrial tachycardia, and finally, atrial flutter.  We are going to discuss these arrhythmias one by   one. This image shows all the common causes  for regular narrow-complex tachyarrhythmia.  

First we will discuss on AVNRT. So, what  is the problem or where is the problem?   There is problem within the AV  node. Let us see what is it. In patients who are prone to have AVNRT,  there will be 2 pathways within the AV  

node. This is a slow pathway which conducts  very slowly but has a short refractory period.   And this is a fast pathway which conducts  fastly, but it has a long refractory   period. That means, it takes some times  to conduct another impulses. Normally,  

the impulses will be conducted via the fast  pathway with the resultant normal PR interval.   So, during the episode of AVNRT, what happens?  An atrial ectopic occurs at critical time. So, this ectopic enters the AV node. And at  the upper part of the AV node, it finds out  

that the fast pathway has not yet recovered after  conducting an impulse. So, it will not conduct an   impulse right now. So, the impulses will pass  via the slow pathway to activate the ventricles   with the resultant widening of the PR  interval. In the lower part of the AV node,  

it finds out that the fast pathway is  now ready to conduct an impulse. So,   this impulse will go retrogradely through the  fast pathway to the upper part of the AV node. From the upper part of the AV node, the impulses  will be conducted back to the atrium to activate  

the atrium, as well as, via the slow pathway  to activate the ventricles. This cycle goes on,   unless you are going to give some drug to block  the AV node. Here you have to see one thing.   The atrial activity happens simultaneously with  ventricular activity. So, what is the implication  

of this one? So, you will not be seeing a P wave  during tachycardia if the patient has AVNRT. So, the P waves are often hidden within the  QRS complexes. So, you do not see any P waves.   Or sometimes, the atrial activity happens  just after the ventricular activity,  

and the P wave will be abnormal because it is  conducted from the AV node to the atrium. So,   there will be negative P wave in lead 2, lead  3, aVF happening after the QRS complexes. So,   this is known as pseudo S pattern. And  there will be positive P wave in lead V1.  

You can see this one, know; so,  this is known as pseudo r dash. Next, we will discuss about AVRT. So, what is  AVRT? It is atrioventricular reentry tachycardia;   the classical example for this being WPW  syndrome, Wolff-Parkinson-White syndrome.  

In Wolff-Parkinson-White syndrome, there will  be an abnormal pathway known as bundle of Kent.   So, this connects the atrium to the ventricle,   and this pathway has a has the property to conduct  the electrical impulses. So, the electrical  

impulses will be conducted from the atrium to  the ventricles or from ventricles to the atrium. Normally, the AV conducts the  impulses from the atrium to the   ventricles. The other part of the AV  groove are electrically impermeable.  

So, in patients with AVRT, the electrical  impulses either enter via the AV node, that   is known as orthodromic AVRT; or it enter via the  bundle of Kent, that is known as antidromic AVRT.   First we will discuss on orthodromic AVRT.  So, in orthodromic AVRT, impulses from the  

atrium or from the SA node enters the  AV node. This activate the ventricles. After activating the ventricles via the bundle of  Kent, the electrical impulses travel back to the   atrium to activate it. Then it enters the AV node,  and the cycle goes on, unless you are going to  

give some drugs to block the AV node. Antidromic:  There will be abnormal conduction via the bundle   of Kent to the ventricles. The impulses will  return to the atrium via the His Purkinje system.   So, what are the ECG manifestations? The rate  is usually around 200 to 300 beats per minute.  

In this example, so, that is  tachycardia, you look at V1. There is some abnormality in the top of the  T waves. So, this is caused by retrograde P   waves that is falling on the T waves. So, whenever  you come across tachycardia and if you are not  

going to find out P wave, you carefully look  at the QRS complexes, ST segment and T wave for   any deformity. The deformity may be produced  by superimposition of the P waves. And next,   we are going to discuss on ectopic atrial  tachycardia. So, there is atrial impulses formed.

And these impulses will be conducted  to the atrium to activate it,   as well as the ventricles, via the AV node. As the  impulses start not from the SA node, but from some   other part of the atrial tissue, there will be  abnormalities in the P wave. You must be knowing  

that P wave should be upright in lead  2, lead 3 and aVF. If the P waves are   inverted in lead 2, lead 3 and aVF, you  have to suspect ectopic atrial origin   of the impulses. So, commonly, this ectopic  or focal atrial tachycardia starts from the  

right lower part of the atrium, so, with the  resultant negative P waves in lead 2, lead 3, aVF. But when you look at the rhythm strip, all the P  waves are similar; even though they are inverted,   they are similar. It means, the impulses start  from single focus. Finally, we are we are going  

to discuss on atrial flutter. In atrial flutter,  the electrical activity will be moving around the   tricuspid valve annulus. That is a typical  atrial flutter. So, the impulses will activate   the atrium as well as the ventricles via  the AV node. So, what are the ECG changes?

So, there will be regular atrial activity.  It will be around 300 beats per minute,   but not all the impulses will be conducted to the   ventricles. There will be block at the level of AV  node. So, the, there will be block within the AV  

node. The block maybe at in the pattern of 2 is to  1, 3 is to 1 or 4 is to 1. If the block is fixed,   you get regular narrow-complex tachyarrhythmia. If  the block is variable, sometimes it conducts with   2 is to 1 block, sometimes with 4 is to 1 block,  you get irregular narrow-complex tachyarrhythmia.

To say atrial flutter, there should be negative  flutter waves in lead 2, lead 3, aVF. Do you see?   So, this is the negative flutterwave.  It resembles sawtooth waves.   So, in lead 2, lead 3, aVF, there  should be sawtooth pattern. And  

in V1, you see uprigh upright flutterwaves.  They resemble normal P waves. So, when you come   across an ECG with regular narrow-complex  tachycardia, you are going to look for P   waves. If they are, you are unable to find  out the P waves, you have to suspect AVNRT.

If the P wave is there, now calculate the  atrial rate. If the atrial rate is greater   than the ventricular rate, you suspect atrial  flutter or ectopic atrial tachycardia. If not so,   you are going to analyse the RP interval. So,  what is the meaning of this RP interval? It means,  

from the beginning of R to the beginning  of P wave during normal sinus rhythm.   This is PR interval, beginning of P to the  beginning of R; this is PR interval. You   compare this PR interval with RP interval, from  the beginning of R to the beginning of P wave.

So, during normal sinus rhythm, the PR  interval is short compared to the RP interval.   But during some arrhythmias, we have discussed  about AVNRT, the PV happens immediately after the   QRS complexes. So, the RP is very short compared  to the PR interval. So, if the RP interval is less  

than 90 milliseconds, you have to suspect AVNRT.  So, we have discussed about regular narrow-complex   tachyarrhythmia. Now, we are going to discuss  on irregular narrow-complex tachyarrhythmias. There are only 3 common causes for this one.  The commonest cause for irregular narrow-complex  

tachyarrhythmia being atrial fibrillation. There  is no organised atrial activity. You see multiple   atrial wavelets, but they do not activate the  atrium as such. So, there is no coordinated   atrial activity; so, there will be no P wave. But  if there is no atrial contraction, there will be  

stagnation of blood. Whenever there is stagnation,  there is increased risk of clot formation. This clot can dislodge, can enter any part of  the body, either the systemic circulation or   pulmonary circulation. If it enters the cerebral  circulation, this leads to cardioembolic stroke.  

We have already discussed about atrial  flutter. If there is atrial flutter and   variable block at the AV node, you get  irregular narrow-complex tachyarrhythmia.   The last one being multifocal atrial tachycardia;  there are multiple areas of impulse formation  

within the atrium. But these impulses, they  activate the atrium as well as the ventricles. To say multifocal atrial tachycardia,  at least you have to find out   3 different P wave morphology. This is 1; this  is 2; this is third. You see all the P waves,  

they are different. This multifocal atrial  tachycardia is commonly associated with   obstructive airway disease like COPD, chronic  obstructive pulmonary airway disease and   pneumonia. So, when you see an ECG with  irregular narrow-complex tachyarrhythmia,  

look at the P wave. If the P wave is absent, you  are going to say this is atrial fibrillation. So, you do not see any P wave; this is QRS  complexes, T wave; there is no P wave at all.   But sometimes, you come across ECG with a  coarse baseline. These are fibrillating waves,  

but not the P waves. You should not confuse  fibrillating with, fibrillating waves with   P waves. This happens in patients  with recent onset atrial fibrillation.   To say atrial flutter, there should be flutter  waves in sawtooth pattern, in lead 2, lead 3, aVF.  

And multiple P wave morphologies  suggest multifocal atrial tachycardia. Now, we are going to discuss on wide-complex  tachycardia. So, what are the causes for   wide-complex tachycardia? We have already  divided the wide-complex tachycardia into  

regular and irregular WCT. So, what are the common  causes for regular WCT? Ventricular tachycardia,   this is the commonest cause; or supraventricular  tachyarrhythmia with aberrant conduction.   What is the meaning of aberrant conduction?  There is problem either the there is right  

bundle branch block or left bundle branch  block or there may be an accessory pathway. These are the 2 common causes for regular WCT.  And irregular WCT may be caused by polymorphic VT.   It means there are multiple foci of  impulse formation within the ventricles.  

Or, atrial fibrillation with aberrant  conduction; you know the meaning of aberrancy.   We have already discussed that this ECG  shows regular wide-complex tachyarrhythmia.   So, what are the differential  diagnosis? Either this is VT  

or SVT with aberrant conduction. Can you  differentiate VT from SVT by looking at the ECG? Yes, there are so many criterias  to differentiate VT from SVT,   the commonly used one being Brugada's.  So, if you come across an ECG with regular  

wide-complex tachyarrhythmia, look at the QRS  morphology and compare it with the QRS morphology   of the previous EC ECG that was  taken during normal sinus rhythm.   If both are similar, you say it is SVT  with aberrant conduction. If the previous  

ECG is not there, you look for typical RBB or LBB  pattern. If it is there, you are going to say SVT. If both are not there, then you are going  to apply the Brugada's algorithm. I have   taken only few points of Brugada's algorithm. You  have to read fully about the Brugada's algorithm.  

It says, you look for concordance.  What is the meaning of concordance?   You look at the chest leads from V1 to  V6. You look at all the QRS complexes.   Here, all the QRS complexes are negative  or below the baseline. So, this is known  

as negative concordance. In the second example,  all the QRS complexes are above the baseline. You are going to call it as positive  concordance; uniformity, you can say uniformity.   So, if there is concordance pattern, it is  diagnostic of VT. If it is not there and you are  

going to find out any RS complexes, what we are  going to do? If there is RS complexes from V1 to   V6, you are going to assess the distance between  the beginning of R; this is the beginning of R; to   the nadir of S wave. So, assess the distance. If  it is more than 100 milliseconds, it is diagnostic  

of VT. And if there is slurring at the lowermost  point of SV, it is also diagnostic of VT. You have to apply all other criterias  to say whether it it is VT or SVT. So,   what are the contributing factors? You look for AV  dissociation. You must be knowing the terminology.  

The atrium; the star says atrial activity.   So, these are the atrial activation, and these  are the ventri uh uh QRS complexes caused by   ventricular activation. There is no relationship  between atrial activity and ventricular activity.  

Atrium is contracting on its own,  and the ventricles are contracting   on their own; no relationship between  atrial and ventricular activity. If it is there, it is diagnostic of VT. And  you look for capture or fusion beat. So,  

what is the meaning of capture beat? You  compare these QRS complexes with this one.   Compared to this QRS complex, this QRS  complex is narrow and it is preceded by a   P wave. So, what is the meaning of capture  beat? It means, during the episode of VT,  

the sinus impulse may be conducted  via the AV node and temporarily   captures the ventricle. That means, the  ventricle is activated by the sinus impulse. So, you see P wave, normal PR interval  and normally looking QRS complexes;  

it is diagnostic of VT. And you look for  fusion beat. What is the meaning? The   ventricles are activated partly by the  conducted impulses from the sinus node   and partly by the ventricular ectopic.  So, it is fusion between the two.  

So, in ECG with VT, you may also find out axis  which is north-west. And you assess the duration   of the QRS complexes. When the duration is more  than 160 millisecond, it is also suggestive of VT. So, we are finally coming to the end. So, whether  it is VT or SVT with aberrant conduction? So,  

we are going to apply the Brugada's. Is  there any concordance? No concordance.   Some of the complexes are positive. And  predominantly, here you see negative complexes.   But you see RS complexes from V1 to V6. So, now  we are going to assess the RS interval. It means,  

from the beginning of R wave. So, this is the  beginning. I am sorry, this is the beginning. This is the beginning of the R wave, to the  nadir of S wave. So, you 1, 2, 3, 4; so,   it is more than 100 milliseconds. It is diagnostic  of VT. So, when you come across an ECG like this,  

you have to alert your team immediately. Probably  the patient may be having myocardial ischemia   or infarct. You have to recognise  it and treat it promptly. To sum up.   So, we are going to see an ECG and  find out that the rhythm is abnormal.  

So, this is an abnormal rhythm. We do not see any P waves. Okay. This  is an abnormal rhythm. You are going to   find out the rate. So, how are we going to  calculate the rate? Here, the QRS complexes  

occur at irregular interval or haphazardly.  So, here you cannot use 300 divided by   number of large boxes or 1500 divided by  number of small boxes between the R waves.   So, you have to calculate the number of QRS  complexes in 30 large boxes and multiply it  

by 10. This has been discussed already.  So, how many QRS complexes are there? Approximately 14; and multiply it by 10; so, the  rate is 140. So, this is tachyarrhythmia. So,   first find out what is the rate; then, whether  whether the rhythm is normal or the rhythm is  

abnormal. If there is tachyarrhythmia, you  are going to approach in stepwise manner.   So, you are going to see whether this  is a narrow-complex tachyarrhythmia or   a broad-complex tachyarrhythmia. Let us calculate  the QRS duration. It is less than 2 small boxes.  

Okay. So, it is less than 120. So, this is  a regular narrow-complex tachyarrhythmia. If it is regular narrow-complex  tachyarrhythmia, you are going to   find out whether the QRS complexes occur  at regular interval or irregular interval.  

These QRS complexes occur  at irre irregular interval.   So, this is a, this is an example for irregular  narrow-complex tachyarrhythmia. What are the   differential diagnosis? Only 3 possibilities.  Atrial fibrillation when the commonest cause;  

atrial flutter with variable AV block  and multifocal atrial tachycardia. So,   we are going to look for P waves if there  is irregular narrow-complex tachyarrhythmia. So, in the rhythm strip, we are going  to look for P waves. Do you see any P  

wave? This is a QRS complex, ST segment and  T wave, no P wave; QRS complex, ST segment   and T wave. You see some coarse baseline,  especially in V1, you see coarse baseline, they   are actually not P waves. So, it is indicative  of atrial fibrillation, probably of recent onset.  

So, this is about tachyarrhythmias. Next, we are  going to discuss on premature ventricular complex. It is self-explaining. There is a  premature beat starting from the ventricle   and activate both the ventricles. We  usually call it as ventricular ectopics.  

How are we going to find out  the ventricular ectopics?   You look at all the QRS complexes, 1, 2, 3,  4, 5, 6, 7; after 7, 2 complexes are abnormal.   The remaining 5 complexes are normally  conducting sinus impulses as manifested by  

P wave under normally appearing QRS  complexes. So, this QRS complex is broad. You calculate the duration; 1, 2, 3;  so, it is more than 120 millisecond.   So, there is a broad QRS complex and it  occurred early. We expect the normal sinus beat  

here, but this ectopic has happened early.  And you look at the ST segment and T wave.   Compared to the ST segment and T waves  of the normally conducted sinus beat,   these ST segment and T waves are bizarre.  

These are known as secondary ST tegment,  secondary ST segment and T wave changes. Where do you come across primary ST segment  and T wave changes? In patients with   myocardial ischemia. And look for compensatory  pause. What is the meaning of it? You are going  

to assess the distance between the sinus  rhythm which happened before the ectopic   and after the ectopic. This duration will be twice  that of the normally conducting sinus impulse. So,   where do you come across incomplete compensatory  pause? In patients with atrial ectopic.

These are the few terminologies used  to describe ventricular ectopics. What   is the meaning of unifocal ectopics? In a  rhythm strip, all the QRS complexes will be   similar. Okay. This means, they have started  from single focus. And multifocal VPCs, in  

in a rhythm strip, the QRS morphologies will  be different. It means there are multiple foci   within the ventricles. And what is the meaning of  bigemini? It is associated with digoxin toxicity. There will be a normal sinus rhythm, ectopic  and a pause, sinus rhythm, ectopic and pause;  

this goes on. This is bigemini.  And then, trigemini; 2 normal   sinus beat followed by an ectopic and  pause; this cycle goes on. Thank you.