Clin Med II: Exam 9: Conduction Disorders

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myocardial cells

cells of the heart with contractility and extensibility.

Electrical cells

cells that initiate electrical activity, exitability, and conductivity in the heart.

Depolarization

Loss of a state of polarity; loss or reduction of negative membrane potential

Repolarization

Return of ions to resting state Muscle cells relaxed (J point, ST segment, T waves, and U wave) (recharging to prepare to fire again)

Sinoatrial node -->

AV node-->

Bundle of His-->

Bundle Branches-->

Purkinje fibers

Describe the normal impulse conduction.

0.7-.12

What is the duration of the P wave?

.07-.11

What is the normal duration of the QRS complex?

0.12-0.20

What is the normal duration of the PR interval?

SA node is depolarizing slower than normal, but impulse conducted normally.

What is the etiology of sinus bradycardia?

increased vagal tone

What is the most common cause of sinus bradycardia?

True

T/F, sinus brady is usually an incidental finding.

beta-blockers, digitalis, calcium channel blockers, amiodarone, cimetidine, lithium

Others:SLE, collagen vasc diseases

infiltrative diseases (sarcoid, amyloid)

What are some drugs that could cause sinus brady?

Normal aging

Acute MI esp. affecting inferior wall

Hypothyroidism

Hypothermia

Hypokalemia

What are some other medical causes of sinus brady?

micturation and coughing

In what situations might sinus brady present?

Sick sinus syndrome, but survival rates can improve with a pace maker

Sinus brady has a poor prognosis in pts with what?

•Most often asymptomatic.

•Syncope

•Dizziness

•Lightheadedness

•Chest pain

•Shortness of breath

•Exercise intolerance

•Pertinent elements of history

What are the most common symptoms of sinus brady?

Decreased LOC

Cyanosis

Peripheral edema

Pulmonary vascular congestion

Dyspnea

Poor perfusion

Syncope

Other than slow, regular heart rate, what might be seen on PE in sinus brady?

Electrolyte levels

Glucose

Calcium

Magnesium

Thyroid function tests

Toxicologic screen

12 lead EKG

What diagnostic studies can be done for sinus brady?

True

T/F, no tx is needed for sinus brady is it is asymptomatic.

direct is at the underlying cause

If a pt comes to the ER with sinus brady and they are hemodynamically stable, what should tx be directed at?

-atropine

-endotracheal intubation and transcutaneous or transvenous pacing

-continuous cardiac monitoring and IV access

If a pt comes to the ER with sinus brady and they are hemodynamically unstable and present with syncope, cheat, and pain, what should tx be directed at?

True

T/F, tx for sinus brady should only be done for hemohynamic unstable/symptomatic (hypotension, altered mental status, ischemic chest pain, and acute HF).

Calcium chloride 10% IV in 100-500mg boluses

What should be used in sinus bradyin cases of CCB toxicity?

Glucagon IV in 2-4 mg boluses

What should be used in sinus brady in cases of B-blocker toxicity?

•Atropine sulfate IV 0.5-1.0mg boluses

•Isoproterenol IV 1-4 mcg/min

•Calcium chloride 10% IV in 100-500mg boluses for cases of CCB toxicity

•Glucagon IV in 2-4 mg boluses in cases of B-Blocker toxicity

Describe the overall tx for hymodynamic unstable/symptomatic sinus brady?

True

T/F, in sinus tachycardia the SA node is depolarizing faster than normal.

False, sinus tachy is a response to physical or psychological stress, NOT a primary arrhythmia.

T/F, sinuc tachycardia ia a primary arrythmia.

-Fever

-Hyperthyroidism

-Effective volume depletion

-Anxiety

-Pheochromocytoma

-Sepsis

-Anemia

-Exposure to stimulants (nicotine, caffeine) or illicit drugs

-Hypotension and shock

-PE

-Acute coronary ischemia and myocardial infarction -

If Post MI-poor prognostic sign

-Heart failure

-Chronic pulmonary disease

-Hypoxia

What are some various causes of sinus tachy?

decreases cardiac output

In patients with organic disease/sustained tachycardiac, the increase in HR _____________ the cardiac output by shortening ventricular filling time.

exacerbates coexisting myocardial and/or valvular heart disease

In patients with organic disease/sustained tachycardiac, the increase in HR exacerbates coexisting what?

increases

In patients with organic disease/sustained tachycardiac, the increase in HR ___________ myocardial oxygen consumption.

reduces coronary blood flow (b/c the heart recieves blood during diastole)

In patients with organic disease/sustained tachycardiac, the increase in HR reduces what?

True

T/F, the management of sinus tachycardia is mainly based on underlying cause.

beta blockers

If sinus tachycardia is present, but no etiology is found but is bothersome to the patient, how can you treat it?

sinus arrhythmia

What arrhythmia presents with variations in the cycle lengths between p waves/ QRS complexes. It will often sound irregular on exam. Normal p waves, PR interval, normal, narrow QRS.

True

T/F, sinues arrhythmia is usually due to a respiratory cause.

inspiration

In sinus arrhythmia shows an increase in heart rate during _____________.

children

Sinus arrhythmia is usually exaggerated in ___________, young adults and athletes. It decreases with age.

seen in digitalis toxicity

What is one of the main non-respiratory causes of sinus arrhythmia?

Sick Sinus Syndrome (SSS)

What arrhythmia presents as sinus bradycardia (rate of about 43 bpm) with a sinus pause?

True

T/F, sick sinus syndrome is often a result of tachycardia-bradycardia syndrome.

tachycardia-bradycardia syndrome

•A burst of atrial tachycardia (such as afib) is then followed by a long, symptomatic sinus pause/arrest, with no breakthrough junctional rhythm.

•Sinus node fibrosis,

•SNode arterial atherosclerosis,

•Inflammation (Rheumatic fever, amyloid, sarcoid)

•Occurs in congenital and acquired heart disease and after surgery

•Hypothyroidism

•Hypothermia

•Drugs: Digitalis, lithium, cimetidine, methyldopa, reserpine, clonidine, amiodarone

What are some common causes of sick sinus syndrome?

False, most are elderly, and may or may not have symptoms.

T/F, most pts that present with sick sinus syndrome are young.

•Address and treat cardiac conditions

•Review med list,

•Labs such as CBC, TSH, etc

•Pacemaker for most is required: Refer to cardiology

What is the management of sick sinus syndrome?

-premature atrial contractions (PACs)

-premature ventricular contractions (PVCs)

What are the two types of premature beats?

in the atria, but NOT in the SA node

The contour of the P wave, the PR interval, and the timing are different than a normally generated pulse from the SA node

Where do PACs originate from, describe what a PAC looks like?

Excitation of an atrial cell forms an impulse that is then conducted normally through the AV node and ventricles

What is the etiology of PACs?

atrial fibrillation

What might PACs lead to in pts with heart disease?

•Most often asymptomatic.

•Palpitations

•Palpation of the peripheral pulse will demonstrate either premature pulse waves or pauses related to PACs

•May lead to atrial fibrillation in pt's with heart disease

•Early sign of CHF or electrolyte imbalance in pt with MI

What are symptoms of PACs?

no therapy is required

What is the tx for PACs in an asymptomatic pt?

True

T/F, you should tx the underlying cuase of the PACs.

•Reassurance of benign nature of PAC

•Determine trigger and tailor pt education

•Discontinue potential precipitating factors

•Caffeine , ETOH or smoking cessation

•Stress reduction techniques

Describe the tx of PACs in symptomatic pts.

a beta blocker

If necessary, medical therapy for PACs should begin with what?

Type II second degree AV block

*P-P interval is regular in Type II block*

Make sure to not confuse a PAC with what?

Preventricular Contraction (PVC)

•Ectopic beats originate in the ventricles resulting in wide and bizarre QRS complexes.

uniform

What is it called when there are more than 1 PVC premature beats and they look alike?

multiform

What is it called when PVCs look different?

irritability

One cause of PVCs is electrical ___________ in ventricular conduction.

cardiac cycle

Ectopic PVC beat can occur early or late in the _________ _______.

superimposed on the T wave of preceding complex - "R-on-T"

*may initiate V tach or V fib in pts with underlying heart disease*

What would you expect on ECG with an early ectpic beat?

abnormally conducting through the ventricles

In PVCs one or more ventricular cells are depolarizing AND the impulses doing what?

men> women, african american compared to whites, and in those with organic heart disease

Who are PVCs more frequent in?

-hypokalemia

-hypomagnesemia

-hypertension

PVCs are increased with age and in the presence of what other factors?

80%

24hr holter will show PVCs in up to _______% of healthy persons monitored.

True

T/F, PVCs are seen in 58-89% of pts with mitral valve prolapse.

Couplets or triplets

Multiformed

Bigeminy or Trigeminy

R on T phenomenon in pts with an acute event

Describe the dangers of PVCs.

•Palpitations

•Syncope in patients with bradycardia

•Presyncope

•Dizziness

•Hypotension

•Auscultated compensatory pause

What are the S&S of PVC?

•CBC

•TSH

•Electrolytes if on diuretics

•CXR

•Echocardiogram

•Treadmill stress test

•Holter

•Event monitor

What diagnostic studies should be done for PVCs?

-presence of underlying structural disease: Beta blockers prior MI or HF, antiHTN therapy to induce regression of LVH

-symptomatic: beta blocker and amiodarone

What is included in the PVC management?

•Frequent, symptomatic, and monomorphic PVC's refractory to medical therapy or pt chooses to avoid long-term medical therapy.

•Ventricular arrhythmia storm that is consistently provoked by PVCs of a similar morphology.

When would ablation for PVCs be indicated?

•Atrial Fibrillation

•Atrial Flutter

•Paroxysmal Supraventricular Tachycardia

What are included as supraventricular arrhythmias?

irregularly irregular

What is the characteristic rhythym of AFib?

False, it is common.

T/F, AFib is rare.

P waves

*impulses are NOT originating form the sinus node*

Afib has no organized atrial depolarization, so no normal ____ waves.

True

T/F, AFib atrial activity is chaotic, resulting in an irregularly irregular rate.

due to multiple re-entrant wavelets conducted b/t the R & L atria.

*OVERALL, impulses are formed in a totally unpredictable fashion*

What do recent theories suggest for the etiology of AFib?

•Advanced age

•Emotional stress

•Surgery

•Exercise

•Fever

•Acute alcoholic intoxication

•Prominent surge of vagal tone (i.e., vasovagal response)

•Metabolic or hemodynamic derangements

•Acute hypoxia

•Cardiovascular disease

•COPD

•Thyrotoxicosis

•Pneumonia

•Pulmonary embolism

What are some risk factor for AFib?

•Palpitations

•Dyspnea

•Chest pain

•Dizziness

•Syncope

•Fatigue

•Exercise intolerance

Although Afib may be asymptomatic, what could be some presenting symptoms?

Systemic embolization (e.g., stroke)

Anxiety secondary to palpitations

Irregular, rapid pulse

Hypotension

Loss of: a waves in the jugular venous pulse (from the loss of atrial kick)

Irregularly irregular rhythm on auscultation

Variation in intensity of first heart sound

What are some signs of Afib on PE?

•Toxicologic screen: ALCOHOL (some tox screens don't include alcohol), Cocain, etc.

What is a KEY diagnostic study when a pt presents with AFib, especially if they are younger in age?

•CBC

•Electrolyte levels

•Glucose

•Calcium

•Magnesium

•Thyroid function tests

•Toxicologic screen: ALCOHOL (some tox screens don't include alcohol), Cocain, etc.

•12 lead EKG

What are the diagnostic studies that should be done for a pt with AFib?

•Assess onset of sxs—

•In the last 24-48 hours?

•Sudden onset?

•Associated symptoms? (sob, chest pain, etc) Or no sxs?

•Assess heart rate, edema (signs of failure)

What are important questions in the H&P for AFib?

echo

What diagnostic test could be done in a pt with AFib to evaluate valvular and overall function?

SYNCHRONIZED cardioversion with heparin

What is the recommended tx for Afib if onset is within last 24-48 hrs?

anticoags FIRST

-need 4-6 weeks of anticoagulation therapy prior to cardioversion and then warfarin for 4-12 weeks after

What is the recommended tx for AFib if unable to DEFINITELY conclude onset in last 24-48 hrs?

SYNCHRONIZED cardioversion STAT

What is the tx for a pt with AFib that is unstable?

TEE b/c the pt is high risk for thrombus

If pt with AFib has possible valvular disease, what is needed?

True

T/F, overall Afib is a stable rhythm and can be managed with RATE CONTROL PLUS chronic anticoags.

•Beta-blockers (atenolol and metoprolol)

•Calcium channel blockers (verapamil or diltiazem)

•Digoxin: Recommended for rate control, especially if hypotensive and HF.

What types of medications can be used in Afib for rate control?

•LMWH and then change/bridge over to warfarin

•Can use aspirin if CI to warfarin, but not as effective

•Sometimes on combination of antiplatelets and anticoagulation (heparin and warfarin)

What is the recommended anticoagulation for pts with Afib?

2.5 (2.0-3.0)

What is the INR goal for Warfarin (Coumadin) anticoag?

True

T/F, radiofrequency ablation is also a possible tx for Afib.

clot formation and subseguent thromboembolic events --> STROKE

•In elderly patients with AF, the attributable risk for stroke approaches 30%.

What is the MAIN complication with Afib?

•Hypotension

•Cardiac ischemia

•Syncope

•Heart failure

•Other arrhythmias

•Pulmonary edema

•Cardiomyopathy (tachycardia-induced)

Other than clot formation and possible stroke, what are some other possible complication of Afib?

sawtooth pattern on EKG

What is characteristic of Aflutter?

True

T/F, usually every other impulse is conducted through the AV node in Aflutter.

250-350 bpm

What is the typical range for rate in Aflutter?

•Reentrant pathway in the right atrium with every 2nd, 3rd or 4th impulse generating a QRS

What is the etiology of Aflutter?

COPD, rheumatic or coronary heart disease, heart failure, ASD, surgical repair of congenital heart disease.

What things are most often associated with Aflutter?