Misplacement of precordial leads

Tracing 4A: Reversal of electrodes V1 and V5 with a tall R wave in V1 and poor R wave progression in the precordium in V5;

Tracing 4B: Inversion of V1 & V2

Reversal of electrodes V1 and V2; the pattern is more difficult to identify; the R wave is taller in V1 than in V2 contrary to the S wave;

Tracing 4C: V1 &V2 Two intercostal spaces too high

Placement of V1 and V2 electrodes two intercostal spaces too high; incomplete right bundle block pattern with rSr’ complexes;

Tracing 4D: V1 & V2 Two intercostal spaces too low

Placement of electrodes V1, V2, V3 two intercostal spaces too low; early transition with R/S ratio > 1 from V2 onward;

Comments: Misplacement of precordial electrodes is common and can be divided into reversal of two precordial electrodes and displacement of one or more electrodes one or two intercostal spaces above or below the recommended sites. They can lead to misdiagnosis, the leads no longer exploring the desired area.

• a reversal in the placement of two precordial electrodes (e.g. V1 with V2, V4 with V5 or V1 with V5) can be suspected in the absence of smooth R wave progression from V1 to V5 or by the absence of the usual pattern of morphology progression in the precordium (from a rS pattern in V1-V2 to a Rs pattern in V5-V6); the more remote the inverted electrodes (V1 with V5 for example), the more abrupt the change in QRS morphology compared to the previous complex with a return to the expected morphology on the following complex; the electrical pattern can thus appear highly pathological and lead to a misdiagnosis (false right ventricular hypertrophy if reversal between V1 and V5 with presence of a prominent R wave in V1);
• the misplacement of one or several precordial electrodes (usually one or two intercostal spaces too high or too low) is more difficult to detect; an electrode can be placed directly on the rib and not in an intercostal space, an electrode can be placed in the wrong intercostal space, electrodes V1 and V2 can be placed too high and electrodes V4 to V6 too low or too posterior; the displacement of electrodes V1 and V2 upward can simulate an anteroseptal infarction or incomplete right bundle branch block (rSr’ pattern); the displacement of electrodes V1, V2, V3, V4 downward produces less prominent changes but may lead to a delayed R wave progression pattern;

Take-home message: A reversal between 2 precordial electrodes is suspected in the absence of smooth R wave progression from V1 to V5.