cardiac 1

SA node 60-100bpm>>internodal pthways-carry impulse from SA node to AV node (slows impulse, allows atria to fully empty b/f contraction of ventricles, can initiate an impulse of 40-60 bpm when SA node isn't functioning>>Bundle of His-connects AV node to RBB and LBB on either side of intraventricular septum>>Bundle branches carry impulses to Perkinje fibers-terminal branches of conduction system initiating contraction through myocardium causing ventricular contraction, can initiate impulses of 20-40 bpm when SA and AV node can't

• fast 6 hrs before study
• an IV is started for administration of sedative and any pharmacologic stress testing medications
• moderate sedation
• pts throat is anestitized b/f probe is inserted
• pt is asked to swallow until correctly positioned in esophagus
• BP, ECG, resp., and O2 sat is monitored
• fast 2 hrs after, sore throat for 24 hrs, if outpatient, someone must transport pt home

• represents the electrical impulse starting in the sunus node and spreading through the atria
• therefore, it represents atrial depolarization
• normally 2.5 mm or less in height and 0.11 sec. or less in duration

• represents ventricular depolarization
• not all QRS complexes have all three waveforms
• the Q wave is the first negative deflection after the P wave
• the Q wave is usually less than 0.04 sec. in duration and less than 25% of the R wave is the first positive defelction after the P wave, and the S wave is the first negative deflection after the R wave
• when a wave is less than 5 mm in height, small letter (qrs) are used, when a wave is taller than 5 mm (QRS) is used
• the QRS complex is normally less than 0.12 sec. in duration

• represents ventricular repolarization of the Purkinje fibers, but it sometimes is seen in pts with hypokalemia, HTN, or heart disease
• if present, the U wave follows the Twave and is usually smaller then the P wave
• if tall, it may be mistaken for an extra P wave

• represents ventricular repolarization when the cells regain a negative charge
• also called resting state
• it follows the QRS complex and is usually the same direction as the QRS complex
• atrial repolarization also occurs but is not visible on the ECG b/c it occurs at the same time as the QRS

• measured from the beginning of the P wave to the beginning og the QRS complex and represents the time needed for sinus node stimulation, atrial depolarization, and conduction through the AV node b/f ventricular depolarization
• in adults, the PR interval normally ranges from 0.12-0.20 seconds in duration

• represents early ventricular repolarization, lasts from end of the QRS complex to the beginning of the Twave
• the beginning of the ST segment is usually identified by a change in the thickness or angle of the terminal portion of the QRS complex
• the end of the ST segment is usually identified by a change in the thickness or angle of the terminal portionof the QRS complex
• the end of the ST segment may be more difficult to identify b/c it merges into the T wave
• identifies cardiac ischemia whether above or below the iso-electric line

• represents the total time for ventricular depolarization and repolarization, is measured from the beginning of the QRS complex to the end of the T wave
• varies with HR, gender, and age, and the measured interval needs to be corrected for these variables through specific calculations
• the interval is usually 0.32-0.40 sec. in duration if the HR is 65 to 95 bpm
• if prolonged, the pt may be at risk for a lethal ventricular dysrhythmia called torsades de pointes

• measured from the end of the T wave to the beginning of the next p wave, an isoelectric period
• when no electrical activity is detected, the line on the graph remains flat, this is called the isoelectric line
• the ST segment is compared with the TP interval to detect changes from the line on the graph during the isoelectric period

• measured from the beginning of one P wave to the beginning of the next
• the PP interval is used to determine atrial rhythm and rate
• the RR interval is measured from one QRS complex to the next QRS complex
• the RR interval is used to determine ventricular rate and rhythm

• a 1 min. strip contains 300 large boxes and 1500 small boxes
• HR=small boxes w/i RR interval and divide 1500/10=150 or 1500/25=60

• anpther method is to count the # of RR interval in 6 seconds and multiply by 10
• RRs are counted instead of QRS complexes
• can also use PP interval for atrial rate-so RR=ventricular rate, and PP=atrial rate

• causes:
• lower metabolic needs-sleep, athletic training, hypothyroidism
• vagal stimulation-vomiting, suctioning, severe pain, extreme emotions
• medications-calcium channel blockers,amiodarone, beta-blockers
• ICP, myocardial infarction (MI) esp of inferior wall

• remember H's and T's:
• H's-hypovolemia, hypoxia, hypoglycemia, hypothermia
• T's-tamponade, tension pneumothorax, thrombosis, and trauma (hypovolemia and IICP)

• tx- prevent further vagal stimulation (defecation, vomiting)
• may have to withhold a medication (beta-blocker)
• if results in SOB, acute alteration of mental status, angina, hypotension, ST segment changes, or premature ventricular complexes
• tx is directed at inc. HR
• tropine 0.5 mg is given rapidly IV to block vagal stimulation, allowing a normal HR to occur
• Rarely, catecholamines and emergency transcutaneous pacing also are implemented

• causes:
• physiologucal stress-acute blood loss, anemia, shock, hypervolemia, hypovolemia, HF, pain, hypermetabolic states, fever, exercise, anxiety
• medications that stimulate the sympathetic response-catecholamines, aminophylline, atropine
• stimulants-caffeine, alcohol, nicitine
• ilicit drugs-amphetamines, cocaine, ectasy
• enhanced automaticity of the SA node and/or excessive sympathetic tone-inappropriate sinus tachycardia
• Postural Orthostatic Tachycardia (POTs)-tachycardia w/o hypotension w.i 5-10 min. of standing with head upright and tilt testing

• characteristics:
• ventricular and atrial rates >100 but ususally <120
• rhythm-regular
• QRS-usually normal, but maybe regularly abnormal
• P wave-normal and consistent shape, always in fromt of QRS, but may be buried in T wave
• PR interval-consistent interval btwn 0.12 and 0.20 sec.
• P:QRS ratio-1:1

• as rate inc., diastolic filling time dec. resulting in syncope, dec. BP, pulmonary edema
• tx-abolish cause, beta-blockers and calcium channel blockers, although rarely used, may be administed to reduce HR quickly

catheter ablation, inc. sodium and fluid intake and compression stockings to prevent pooling in lower extremities-tx for POTS

• sinus node creates an impulse at an irregular rhythm, usually the rate inc. with inspiration and decreases with expiration
• other causes:
• heart disease, valvular disease, does not cause any significant hemodynamic effect and usually is not treated

• rate-60-100
• rhythm-irregular
• QRS-usually normal, may be regularly abnormal
• P wave- in front of QRS, normal and consistent
• PR-0.12-0.20
• P:QRS-1:1

• a single ECG complex that occurs when an electrical impulse starts in the atrium b/f the next normal impulse of the sinus node
• may be caused by caffeine, alcohol, nicotine, stretched atrial myocardium-as in hypervolemia, anxiety, hypokalemia, hypermateabolic states-pregnancy, atrial ischemia, injury, or infarction

• PACs are often seen with sinus tachycardia and have the following characteristics:
• rate-depends on underlying rhythm-e.g. sinus tachycardia
• rhythm-irregular from early P waves, shorter PP interval followed by longer PP interval (noncompensatory pause)

• P wave-early and different P wave may be seen or hidden in the T wave, other P waves in the strip are consistent
• PR-early P wave has shorter than normal PR interval, but still btwn 0.12-0.20 sec.
• P:QRS-usually 1:1
• QRS-follows early P wave and usually normal nut may be abnormal (abberantly conducted PAC), may even be absent (blocked PAC)
• PACs are common in normal hearts, pts say" my heart skipped a beat", apical and radial pulses may be difererent
• if infrequent-no tx
• frequent->6 per min.=worsening disease>>AFIB, tx is directed toward cause

• rate-25-400 times per minute
• b/c atrial rate is faster than the AV node, can conduct, not all atrial impulses are conducted int o the ventricle, causing a therapeutic block at the AV node
• this is an important feature of the dysrhythmia, similar to AFIB
• rate-250-400 atrial rate, usually ventricular rate btwn 75-150
• rhythm-atrial=regular, ventusually reg. but may be irreg. due to change in AV conduction
• QRS-usually normal, may be abnormal or absent
• P-saw toothed-Fwaves
• PR-difficult to determine b/c of F waves
• P:QRS-2:1, 3:1, or 4:1

• s/s:
• chest pain, SOB, dec. BP
• if pt is unstable, electrical cardioversion is indicated
• in addition, rapid atrial pacing (overdrive atrial pacing-atrium paced at a faster arte than that in atrial flutter-may be an alternative to cardioversion esp. in pts who've had cardiac surgery)
• if pt is stable and the QRS is narrow and RR is regualr-give 6 mg of adenosine with 20 ml saline flush and elevation of arm to promote rapid circulation
• if doesn't convert to NSR w/i 1-2 min.-12 mg bolus and repeated if needed w/i 1-2 min
• if adenosine fails or RR interval is irregular, Cardizem or Beta-Blocker IV to slow vent. rate
• these can slow conduction through AV node

• amiodarone, Rhythmol, Tambocor, digoxin, Catapres, or magnesium are given in acute onset
• if med therapy is unsuccessful-electrical cardioversion
• if longer than 48 hrs and TEE has not confirmed absence of atrial clots-anticoag. b/f cardioversion (electrical or chemical ablation)
• after-flecainide, propafenone, amiodarone, or beta-blocker may be given to prevent reoccurance

• causes rapid, disorganized, and uncorrdinated twitching of atrial musculature
• linjked to stroke, HF, dementia, and premature death, and is considered a growing health problem in developed countries
• may be transient and occuring for a short time (paroxysmal), or it may be persistent requiring tx to terminate the rhythm or control ventricular heart disease, coronary artery disease, HTN, HF, DM, hyperthyroidism, pulmonary disease, ETOH, or after open heart surgery
• "lone AFIB"-no underlying pathophysilogy