lec 9 ECG Part II

Flashcards covering ECG rhythm analysis, boxes and sizes, dysrhythmias, J point, and various types of Myocardial Infarction identification based on lecture notes.

What are the two primary learning objectives for the ECG Part II lecture?

Explore rhythm analysis and ECG findings of myocardium ischemia.

In rhythm analysis, what are the three things that should be checked regarding P waves?

If they are present, if they are upright in Lead II, and if they are related to the QRS complex.

What does it mean if P waves and the QRS complex are 'married'?

It means they have a fixed PR interval.

In terms of 'big boxes' on ECG paper, what is the normal duration of a PR interval?

Less than 1 big box ($< 1$ big box).

What is the normal limit for a QRS interval in terms of 'big boxes'?

Less than half a big box ($< 1/2$ big box).

What is the normal limit for a QT interval relative to the RR interval?

Less than half of the RR interval ($< 1/2$ RR).

What is the time duration represented by one little box on EKG graph paper?

$0.04$ second.

What is the time duration represented by one big box on EKG graph paper?

$0.2$ second.

How many millimeters are in one big box on EKG paper?

$5.0\,mm$.

How many big boxes are contained in $2.5$ seconds on an ECG?

$12.5$ big boxes.

Which type of rhythm is associated with a slow rate and transmission from a displaced junctional or nodal location?

Junctional/Nodal rhythms.

What diagnostic abnormality occurs when there are more P waves than QRS complexes?

Heart blocks (slow rate).

Which rhythm category is characterized by a rate that is either fast or absent?

Ventricular rhythms (Ventricular tachycardia, Ventricular fibrillation).

What are two examples of atrial rhythms where the rate varies?

Atrial fibrillation and Atrial flutter.

Diagnosis of arrhythmias depends mainly on what relationship?

The time relations between the different waves of the cardiac cycle.

Why is it important which leads are recorded when diagnosing damage to the Purkinje conduction system?

Because abnormalities of conduction change the ECG pattern in some leads but may not affect others.

Define the 'J Point' in an ECG.

The exact point at which the wave of depolarization just completes its passage through the heart at the end of the QRS complex.

What is the potential voltage at the 'J Point' and why?

Zero voltage, because all parts of the ventricles are depolarized and no current is flowing around the heart.

What serves as the 'Zero Reference Potential' for analyzing Current of Injury?

The J point.

What is the very first sign seen in a normal sinus complex at the onset of myocardial infarction (MI) pain?

The T wave grows taller (Hyperacute T wave changes).

A noticeably elevated ST segment within an hour of pain indicates the onset of what?

Myocardial necrosis (tissue death).

What type of drug should ideally be administered when ST elevation is first noticed?

Thrombolytic (clot-busting) drug.

What specific change on the ECG indicates successful thrombolysis within $90$ minutes?

A $50\%$ reduction in ST segment elevation.

Deep T wave inversion after thrombolysis is a sign of what?

Reperfusion (blood flow returning to the damaged area).

Where would the ST segment typically be $24$ hours after an evolving MI?

Back on the iso-electric line.

How long might T wave inversion persist after an MI?

Days, weeks, or months.

Which ECG wave change is a permanent indicator of myocardial tissue death?

A deep (pathological) Q wave.

Why is a pathological Q wave NOT considered 'time-specific'?

It may be there from a previous heart attack and is not part of the criteria for an Acute Myocardial Infarction.

What are the duration and amplitude criteria usually used to define a 'pathologic' Q wave?

Duration $\ge 0.04\,s$ or $\ge 25\%$ of R-wave amplitude.

What ECG evidence represents transmural injury?

Marked ST elevation with hyperacute T wave changes.

What ECG findings characterize an Inferior MI?

Pathologic Q waves and evolving ST-T changes in leads II, III, and aVF.

In an Inferior MI, in which lead is the pathologic Q wave usually largest?

Lead III.

If an ECG shows ST elevation in leads II, III, and aVF but ST depression in V1-3, what does the depression represent?

True posterior injury.

In an old inferior wall MI, what coronary artery was likely occluded?

Right coronary artery.

What ECG finding in leads V1-3 acts as a 'mirror image' of posterior Q-waves in a True Posterior MI?

Tall R waves.

An old posterolateral MI would show tall R waves and upright T's in V1-3 and a loss of R in which lead?

Lead V6.

In which leads do you look for Q, QS, or QRS complexes to identify an Anteroseptal MI?

Leads V1 to V3 (or V4).

What are the ECG criteria for an Acute Left Main Coronary Artery Occlusion?

ST elevation in lead aVR greater than any in V1, plus ST depression in $7$ or more other leads.

What clinical condition was suspected in the 41-year-old male with 'giant' T-wave inversion in leads I and V4-6 and LVH?

Apical hypertrophic cardiomyopathy (HCM).

List the initial criteria for a Right Ventricular Myocardial Infarction.

Inferior wall MI, ST elevation greater in lead III than II, and ST elevation in V1.

In Right Ventricular MI, what is the significance of ST depression in V2?

It cannot be more than half the ST elevation in aVF.

How much ST elevation is required in right-sided leads ($V4R$ to $V6R$) to suggest RV MI?

More than $1\,mm$.

What are the three steps for evaluating ST segment elevation?

1. Locate the J-point. 2. Identify the isoelectric line. 3. Compare the ST segment level to the isoelectric line.

At what specific time interval after the J point should the ST segment be measured?

$0.04$ to $0.08$ seconds after the J point.

What is the threshold for significant ST elevation in contiguous leads?

More than $1\,mm$ (one small box).

What shape of ST elevation usually indicates acute injury?

Coved shape.

What shape of ST elevation is often benign, especially in asymptomatic patients?

Concave shape.

What defines 'contiguous leads' in the limb leads?

Limb leads that 'look' at the same area of the heart.

What signifies 'ischemia' on an ECG according to 12-lead variations?

Tall or inverted T waves; ST segment may be depressed.

What signifies 'injury' on an ECG according to 12-lead variations?

Elevated ST segment; T wave may invert.

What signifies 'infarction (age unknown)' on an ECG?

Abnormal Q wave, while the ST segment and T wave have returned to normal.

Which leads are used to localize an inferior AMI?

Leads II, III, and aVF.

Which leads are used to localize a septal AMI?

Leads V1 and V2.

Which leads are used to localize an anterior AMI?

Leads V3 and V4.

Which leads are used to localize a lateral AMI?

Leads I, aVL, V5, and V6.

What baseline is used for measuring ST-segment deviation?

PR baseline.

If a patient shows ST elevation in II, III, and aVF but ST depression in I, aVL, V2, V3, and V4, what is the diagnosis?

Inferior wall MI.

Where are leads V7-V9 placed on a patient?

On the patient's back at the $5^{th}$ intercostal space.

In the evolution of AMI, what is the first change seen in the 'first few minutes'?

Tall T wave.

What does the Q wave represent in the evolution of AMI?

Tissue death (permanent marking).

How does 'ischemia' differ from 'infarction' in terms of heart tissue?

Ischemia is the initial myocardial insult/hypoxia, whereas infarction is actual tissue death.

Why does dead tissue from an infarction affect heart function?

Dead tissue no longer contracts; the amount of dead tissue relates to the degree of muscle impairment.

Measurement for significant ST elevation should occur how many seconds after the J-point?

$0.04$ seconds.

Some define alternative significant elevation in limb leads as how many millimeters?

Greater than $2\,mm$ ($2$ small boxes).

Does a normal EKG rule out an acute MI?

No, a normal EKG does not rule out acute MI.

What percentage of patients with inferior MIs also have right ventricular infarcts?

$40\%$.

Why must you watch for hypotension when administering nitrates or morphine to an Inferior MI patient?

Because right ventricular damage may affect contraction, and these drugs can worsen hypotension.

What are the most common heart blocks associated with Inferior MI?

First degree and second-degree Type I (Wenckebach).

Which type of MI is referred to as the 'widow-maker'?

Anterior wall MI.

Why is an Anterior Wall MI called the 'widow-maker'?

Because of the potential for massive sized infarction, cardiogenic shock, and ventricular dysrhythmia.

Which heart blocks are more common in Anterior Wall MI?

Second degree Type II and 3rd degree.

What are 'peaked' T waves?

Pointed T waves that are symmetrical, often seen as the first sign of tissue injury.

What are the normal height limits for T waves in limb and chest leads?

Less than $5\,mm$ in limb leads and $10\,mm$ in chest leads.

Why might T waves become peaked during early injury?

Likely due to potassium leaking through damaged cell membranes (similar to hyperkalemia).

If a patient has ST elevation in II, III, and aVF with a heart rate of $30\,bpm$, what is the rhythm?

Sinus bradycardia (associated with inferior wall MI).

What is the anatomical area 'looked at' by leads I and aVL?

Lateral wall.

What is the isoelectric reference for the ECG?

The line before the P wave or the PR segment.

At the 'J point', how much current is flowing around the heart?

None.

What is the clinical significance of a $50\%$ reduction in ST elevation?

It is a good indicator of successful thrombolysis.

What is the duration of a small box on ECG paper in milliseconds?

$40\,ms$ ($0.04\,s$).

If ST elevation is seen in V2 to V5, what is the location of the infarction?

Anterior infarction.

What is the standard measurement unit for ST segment deviation?

Millimeters ($mm$), with $1\,mm$ equal to one small box.

What condition besides injury causes peaked T waves on an ECG?

Hyperkalemia.

In an Anteroseptal MI, which leads show the most significant evolution of ST-T changes?

V1 through V3.

What is the textbook reference used for the BMS 595 - Human Physiology lecture notes?

Guyton and Hall Textbook of Medical Physiology, 14th Edition.