QIA14Fast & Easy ECGs A Self-Paced Learning ProgramHypertrophy, Bundle Branch Block and Preexcitation

HypertrophyCondition in which muscular wall of the ventricle(s) becomes thicker than normal

Dilation or EnlargementOccurs as result of volume overload where chamber dilates to accommodate increased blood volume

Hypertrophy or EnlargementEnlargement associated with atriaP wave changes used to identify atrial enlargement Hypertrophy associated with ventriclesQRS complex changes used to identify ventricular hypertrophyI

Normal P WaveDuration 0.06 0.10 secondsAmplitude 0.5 2.5 mm First portion represents right atrial depolarizationTerminal portion represents left atrial depolarization

Atrial EnlargementCaused by various conditions Chronic pulmonary disease may cause right atria enlargement in response to the need for greater filling pressures in the right ventricle Mitral valve prolapse may result in blood being forced backwards into the left atria causing it to enlargeA

Atrial EnlargementLeads II and V1 used to assess atrial enlargementI

Right Atrial EnlargementIncrease in amplitude of the first part of the P wave

Left Atrial EnlargementIncreased amplitude in the terminal portion of the P wave in V1Increased duration or width of the P waveI

Ventricular HypertrophyCommonly caused by chronic, poorly treated hypertension Because there is more muscle to depolarize there is more electrical activity occurring in the hypertrophied muscle Reflected by changes in the amplitude of portions of the QRS complexI

Ventricular HypertrophyV1 electrode normally positiveWave of depolarization moving through LV moving away from electrode Produces mainly negative QRS complexes (short R waves with larger S waves)

Right Ventricular HypertrophyMost common characteristic in limb leads is right axis deviationI

Right Ventricular HypertrophyIn precordial leads R waves are more positive in leads which lie closer to lead V1

Left Ventricular HypertrophyIncreased R wave amplitude in precordial leads over LVS waves that are smaller in leads over LV (lead V6) but larger in leads over RV (lead V1) I

Bundle BranchesBundle of His divides into right and left bundle branches Left bundle branch divides into septal, anterior and posterior fasciclesI

Normal QRS Complex Narrow - < 0.12 seconds in durationElectrical axis between 0 and +90I

Bundle Branch BlockLeads to one or both bundle branches failing to conduct impulses Produces delay in depolarization of the ventricle it supplies I

Bundle Branch BlockWidened QRS complexRR configuration in chest leadsI

Right Bundle Branch BlockLook for RR in leads V1 or V2

Left Bundle Branch BlockLook for RR in leads V5 or V6

HemiblocksOccur when one of fascicles of LBB blocked Key to detecting is a change in the QRS axis I

Left Anterior HemiblockI

Left Posterior HemiblockI

Preexcitation SyndromeAccessory conduction pathways sometimes exist between atria and ventriclesBypass AV node and bundle of His and allow early depolarization of ventriclesResults in a short PR interval

Wolff-Parkinson-White (WPW) Syndrome PR interval < 0.12 seconds Wide QRS complexes Delta wave seen in some leads Patients with WPW are vulnerable to PSVT

Lown-Ganong-Levine (LGL) Syndrome Intranodal accessory pathway bypasses normal delay in AV node PR interval < 0.12 seconds , normal QRS complex

Practice Makes PerfectDetermine the type of conditionI

Practice Makes PerfectDetermine the type of conditionI

Practice Makes PerfectDetermine the type of conditionI

SummaryIn hypertrophy the muscular wall of the ventricle(s) becomes thicker than normal. Dilation or enlargement of a chamber occurs because of volume overload where the chamber dilates to accommodate the increased blood volume.

Enlargement is associated with the atria while hypertrophy is associated with the ventricles.

SummaryThe P wave is used to assess for atrial enlargement.

The QRS complex is examined to identify ventricular hypertrophy.

Indicators of enlargement or hypertrophy include an increase in the duration of the waveform, an increase in the amplitude of the waveform and axis deviation.

Leads II and V1 provide the necessary information to assess atrial enlargement.

SummaryDiagnosis of right atrial enlargement is made when there is an increase in the amplitude of the first part of the P wave.

Two indicators of left atrial enlargement are (1) increased amplitude in the terminal portion of the P in V1 (2) increased duration or width of the P wave.

In limb leads, right axis deviation is most common characteristic seen with right ventricular hypertrophy.

SummaryIn precordial leads, right ventricular hypertrophy causes the R waves to be more positive in leads which lie closer to lead V1.

Left ventricular hypertrophy is identified by increased R wave amplitude of those precordial leads overlying the left ventricle and S waves that are smaller in the leads overlying the left ventricle (lead V6) but larger in the leads (lead V1) overlying the right ventricle.

SummaryBundle branch block is a disorder that leads to one or both of the bundle branches failing to conduct impulses. This produces a delay in the depolarization of the ventricle it supplies.

In bundle branch block a widened QRS complex and a RR configuration is seen in the chest leads.

To diagnose right bundle branch block check for an RR in the right chest leads; leads V1 or V2.

SummaryTo diagnose left bundle branch block check for an R, R in leads V5 or V6.

Hemiblocks cause axis deviation.

Preexcitation syndromes occur in some persons because accessory conduction pathways exist between the atria and ventricles which bypass the AV node and bundle of His and allow the atria to depolarize the ventricles earlier than usual.

SummaryCriteria for WPW include a PR interval less than 0.12 seconds, wide QRS complexes and a Delta wave seen in some leads. In LGL there is an intranodal accessory pathway that bypasses the normal delay within the AV node. This produces a PR interval less than 0.12 seconds and a normal QRS.

**Instructional point: The atria dilate more than they hypertrophy. Indicators of enlargement or hypertrophy include an increase in the duration of the waveform, an increase in the amplitude of the waveform and axis deviation.*To demonstrate the mitral valve conditions show the following animation: Mitral Valve Stenosis.

*Instructional point: While P wave changes are given specific names such as P Pulmonale for right atrial enlargement and P Mitrale for left atrial enlargement their presence or absence on the ECG is not diagnostic of any underlying medical condition and should be confirmed by more specific testing such as echocardiography. *Instructional point: Because the duration of time to depolarize the left atria is longer than normal the P wave duration will exceed 0.04 seconds. The P wave may be notched if so the terminal or second portion of the P wave will have a higher amplitude than the initial portion. The P wave may also be biphasic with the terminal portion dipping below the isolectric line. *Instructional point: In patients with thin chests and in particular the young healthy patient the precordial complexes may meet the criteria for hypertrophy with hypertrophy does not exist. This is occurs because of the lower resistance of the thin chest between the heart and the electrode. In this case you may also use the limb leads to further confirm you suspicion. *Instructional point:Rare conditions such as pulmonary hypertension and pulmonary valve stenosis can result in right ventricle hypertophy. When this occurs the primary ECG evidence is right axis deviation as the enlarged right ventricle overshadows the electrical activity of the left ventricle. *Instructional points: Because of the greater mass of the hypertrophied left ventricle the amplitude of the QRS complexes across the precordial leads is most affected because they predominantly overlie the left ventricle. The electrical axis remains normal since the energy of the QRS complex remains downward and to the left.The duration of the QRS may be slightly prolonged in both right and left ventricular hypertrophy. However, it is rarely greater than 0.1 seconds more than normal.*Instructional point: The first and smallest fascicle innervates the interventricular septum and for this reason it is called the septal fascicle. The anterior fascicle carries the impulse to the anterior and superior portion of the left ventricle. The posterior fascicle carries the impulse to the posterior and inferior portion of the left ventricle.*Instructional point: Interruption of normal impulse conduction through either bundle is referred to as a bundle branch block. If one or more of the fascicles is blocked we call this a hemiblock.1 refers to the conduction that continues uninterrupted through the unaffected bundle branch.2 refers to the impulse that activates the intraventricular septum.3 refers to the impulse that activates the other ventricle.For further description see Figure 14-12 of textbook.*Instructional point:The shape of the QRS complex is determined by which bundle branch is blocked. *Instructional points: The most common hemiblocks occur in either the anterior or posterior fasicles.Because the area of impulse blockade is relatively small the QRS duration is generally not affected in either left anterior or left posterior hemiblock.*Instructional point: When the left anterior fascicle is blocked the predominant depolarization of the left ventricle is from the anterior wall around the bottom of the heart and to the left and upwards. This shifts the axis to the left resulting in an axis between 0 and -90 degrees. Lead I will be positive and aVF will be negative. *Instructional point: When the left posterior fascicle is blocked the predominant depolarization is from left right but still in a downward direction. This shifts the axis to the right between +90 and +180 degrees. Lead I will be negative and aVF will be positive. Notes on board pertaining to LVH:R wave V5 or V6 + S wave V1 or V2 >35 mR wave in V5 > 26 mR wave in V6exceeds R wave in lead V5AVL**Answer: Left anterior hemiblock (left axis deviation in the absence of left ventricular hypertrophy).

*Answer: Left ventricular hypertrophy (R wave in V5 + S wave in V2 = 35 mm).

*Answer: Left posterior hemiblock (right axis deviation in absence of right ventricular hypertrophy).