Ventricular Rhythms



Introduction To The 12-Lead EKG

-Anatomy of coronary circulation

-The right coronary artery originates from the right side of the aorta and passes along the atrioventricular sulcus between the right atrium and right ventricle

-The left coronary artery originates from the left side of the aorta and consists of the left main coronary artery that divides into two main branches—the left anterior descending artery and the left circumflex artery

-Hexaxial reference system- represents all of the frontal plane leads with the heart in the center and is the means used to express the location of the frontal plane axis

-Normal axis- 0 to + 89 degrees

-Right axis deviation- + 90 to + 180 degrees

-Left axis deviation- - 1 to -90 degrees

-Indeterminate- “no mans land” or “extreme right axis deviation”, -91 to -179 degrees

-Two-lead method- use leads I and aVF, using QRS direction in the following leads

-Normal- leads I and aVF positive

-Left- leads I positive and aVF negative

-Right- leads I negative and aVF positive

-Indeterminate- leads I and aVF negative

-Ischemia- when the hearts demand for oxygen exceeds its supply from the coronary circulation, represented by changes in T wave an ST segment depression (More than 1 mm below baseline), and reciprocal changes are seen in opposite leads

-Injury- when the period of ischemia is prolonged more than just a few minutes, represented by ST elevation (More than 1 mm above baseline in limb leads an 2 mm in precordial leads), and reciprocal changes are seen in opposite leads

-Infarction- actual death of injured myocardial cells, represented by Q waves, and reciprocal changes are seen in opposite leads

-Non-ST-segment elevation (non-Q-wave) myocardial infarction- the ST segment may be depressed in the leads facing the surface of the infracted area, can only be diagnosed in conjunction with elevations of serum cardiac markers

-R-wave progression- when viewing the precordial leads in a normal heart, the R wave becomes taller and the S wave becomes smaller as the electrodes is moved from right to left

-In V1 and V2, the QRS is predominantly negative

-In V5 and V6, the Q wave is small and R wave is tall

-Poor R-wave progression- R wave that decreases in size from V1 to V4

-Localization of infarctions

-Later wall- leads I, aVL, V5, and V6, usually supplied by the circumflex branch of the left coronary artery, and reciprocal changes in lead V1

-Inferior wall- Leads II, III, and aVF, supplied by the posterior descending branch of the right coronary artery, and reciprocal changes in leads I and aVL

-Septum- Leads V1 and V2, normally supplied by the left anterior descending artery

-Anterior wall- Leads V3 and V4, normally supplied by the diagonal branch of the left anterior descending artery, and reciprocal changes in leads II, III, aVF

-Posterior wall- no leads directly view the posterior wall, can be viewed with tall R waves an ST segment depression, it is supplied by the right coronary artery

Intraventricular conduction delays- are best identified using leads MCL1, MCL6, V1, and/or V6, blood supply is form the left anterior and posterior descending coronary arties

-To identify bundle branch block, QRS must be more than 0.12 seconds and QRS complexes produced by supraventricular activity

-Incomplete right or left bundle branch block- QRS measuring 0.10 to 0.12 seconds

-Complete right or left bundle branch block- QRS measuring more than 0.12 seconds

-To determine right vs. left

-view lead V1 or MCI1

-move from the J point back into the QRS complex and determine if the terminal portion of the QRS complex is a positive or negative deflection

-Right- terminal portion of the QRS is positive

-Left- terminal portion of the QRS is positive

-Atrial enlargement

-Right atrial enlargement- abnormally tall initial part of the P wave, 2.5 mm or more in height

-Left atrial enlargement- the latter part of the P wave is prominent, the P wave is more than 0.11 seconds in duration and often notched

-Ventricular enlargement

-Right ventricular enlargement- right axis deviation and reversal of normal R-wave progression are indications of right ventricular enlargement

-Left ventricular enlargement- deep S waves an small R waves in V1 an V2 also tall R waves an small S waves in V5 an V6, if S wave amplitude in lead V1 added to the R wave amplitude in V5 is greater than or equal to 35 mV, R wave amplitude in lead aVL greater than or equal to 12 mV, and may be accompanied by left axis deviation

-Left ventricular enlargement is not always obvious and many methods are needed to confirm it

-Hypercalcemia- prolonged PR interval and QRS complex also shorted QT interval

-Hypocalcemia- long / flattened ST segment and prolonged QT interval

-Hypermagnesemia- prolonged PR interval an QRS complex and elevated T wave

-Hypomagnesemia- diminished voltage P waves and QRS complexes, flattened T waves, slightly widened QRS complexes, and prominent U waves

-Hyperkalemia- tall / peaked T waves, widened QRS complexes, prolonged PR intervals, flattened ST segments, and flattened or absent P waves

-Hypokalemia- depressed ST segment, flattened T waves, prominent U waves

-Analyzing the 12-lead EKG

-Rate: atrial and ventricular

-Rhythm: atrial and ventricular

-Intervals: PR interval, QRS duration, Qt interval

-Waveforms: P waves, Q waves, R waves (R-wave progression), T waves, U waves

-St segments: elevation, depression

-Axis

-Hypertrophy / chamber enlargement

-Myocardial ischemia, injury, infarction

-Effects of medications and electrolyte imbalances

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