Rightward Shift in Axis or Right Axis Deviation?

December 31, 2006

>Editor’s note: To clearly illustrate the difference between arightward shift of axis and right axis deviation, Dr RichardHarrigan, associate professor of emergency medicine atTemple University School of Medicine in Philadelphia anda regular contributor to CONSULTANT’s “ECG Challenge”feature, provided the 3 ECGs shown here.

Editor's note: To clearly illustrate the difference between arightward shift of axis and right axis deviation, Dr RichardHarrigan, associate professor of emergency medicine atTemple University School of Medicine in Philadelphia anda regular contributor to CONSULTANT's "ECG Challenge"feature, provided the 3 ECGs shown here. The ECG belowshows right axis deviation in a patient with primary pulmonaryhypertension. The 2 ECGs on the following page,from a patient with pneumothorax, show a rightward shiftin the QRS axis.This ECG is from a young woman who presented with dyspnea and was found to have primarypulmonary hypertension. The tracing is notable for borderline sinus tachycardia and evidence ofright ventricular hypertrophy (qR pattern in lead V1 with repolarization abnormality [arrow]; S > Rwave amplitude in lead V6 [asterisk]). There is also evidence of right axis deviation, which in thiscase is a result of the patient's right ventricular hypertrophy. The major QRS vector is negative inlead I and positive in lead aVF (circled complexes). Therefore, the frontal plane QRS axis falls in thequadrant of right axis deviation (somewhere between +90 and 180 degrees). Since lead II (boxedcomplex), with a vector of +60 degrees, features the most isoelectric QRS complex, the frontal planeQRS axis is approximately 90 degrees perpendicular to the +60 degree vector, and somewhere between+90 and +180 degrees; this makes it approximately +150 degrees.These 2 ECGs are from the same patient, at 2 different points in time. In the first tracing (A),the frontal plane QRS axis is approximately +60 degrees. The major QRS vector is positive in leadsI and aVF (circled complexes), which signifies that the QRS axis lies somewhere between 0 and+90 degrees (the vectors of leads I and aVF, respectively). Lead aVL (boxed complex) is almost isoelectric--ie, the positive and negative deflections of the QRS complex are roughly equal. Thus, thefrontal plane QRS axis vector lies roughly 90 degrees perpendicular to the vector of aVL (which is-30 degrees)--within the normal axis quadrant (between 0 and 90 degrees); this yields an axis of+60 degrees.In the second tracing (B) the QRS axis is approximately -10 degrees. In contrast to the firsttracing, the major QRS vector is still positive in lead I but now is just barely negative in lead aVF(circled complexes); thus the QRS axis lies somewhere between 0 and -90 degrees. In this tracing,lead aVF is also the closest to being an isoelectric complex (boxed complex). Therefore, thefrontal plane QRS axis vector is roughly 90 degrees perpendicular to the vector of aVF (which is+90 degrees) within the left axis quadrant (between 0 and -90 degrees). This yields an axis ofroughly -10 degrees, which was the patient's baseline frontal plane QRS axis.This rightward shift in QRS axis--to +60 degrees in A from a baseline of -10 degrees, asshown in B--was the result of a right-sided pneumothorax. The first tracing (A) was recordedwhen the patient presented with chest pain and an unsuspected spontaneous pneumothorax. Thesecond tracing (B) was taken after a chest tube had been placed. Rightward QRS axis shift can beseen with acute pulmonary processes, such as pneumothorax and pulmonary embolism.