To determine if the origin of an ventricular ectopic lies within the RVOT look at the inferior leads and the initial R wave in the precordial leads. . All three of the inferior leads use a positive recording electrode located below the heart.  A ventricular ectopic originating in either outflow track will have a positive deflection in these leads.

          The second step is to determine right or left breakout. This is done using the precordial leads, V1-V6. The key to differentiating RVOT from LVOT lies in where the first R wave is visualized in these leads. If an R wave can be seen in V1 or V2, it suggests that the point of breakout lies within the LVOT. If the R wave does not present itself until V3, then a breakout within the right ventricular output is indicated.

          This is an alternate view of the 12 lead with all the leads shown in a vertivle display. This view is often used during EP studies.

          On either of the 12 lead recordings used, the positive deflection in the inferior leads and the transition in the precordial leads should be noted.

          These indicators help confirm RVOT breakout.

          A single run of VT is displayed using a faster sweep speed. This allows us to read the cycle length measured by the EP recording system easier.

          Most RVOT PVC's and VT's are focal in nature and are thus, a result of an abnormality of automaticity. (For more info, see the section of Focal Tach's.) Note the cycle length changes during this run of VT. The initial rate is 380ms. This decreases to 400ms, then to 420ms, 450ms and finally to 550ms where the run terminates. Whenever you see a tachycardia that displays variable rate of this type, you can be pretty certain you are dealing with a focal tach.

              It is also worth noting what happens to the arterial pressure during tachycardia. While many patients may tolerate RVOT VT without a significant pressure drop, it is also possible that patients experience a hemodynamically signifficant decrease in pressure.

          Another interesting event on the preceeding recording is a catheter induced PVC that is referred to as a "bump". When the RF catheter is being positioned and inadvertantly "bumps" the wall, it often causes an ectopic that is different from the recorded morphology.

          In the displayed leads, the morphology of the third beat is notably different that the other recorded beats. It also occurs significantly earlier and "out of sync" with the other beats in this run. An analysis of the timing between the onset of signal at the RF catheter and the onset of surface ECG show that the intracardiac signal initiates much ealier than the onset of surface for this beat only! This is a good indication of an ectopic caused by moving the RF catheter.

          One of the conventional mapping tools used in determining the origin of focal ectopics is a pacing maneuver referred to as pace mapping. This technique is performed by pacing from the RF catheter when it is believed to be at, or close to, the suspected location of breakout for the beat of interest. (For more information on pace mapping, see the page on Pacing Maneuvers.)

          Pace mapping is performed by splitting the review screen into two windows. The first window is a recording of the surface 12 lead of the clinical VT. The second window shows a 12 lead of the paced morphology. Each lead of the two recordings is reviewed to determine if a 12 of 12 match is obtained. In this case, there is substantial difference between the two displays. We are not at the ideal location to target ablation energy.

          By moving the ablation catheter around and pacemapping at a number of different locations, a good 12 of 12 match is located.

          This degree of correlation between the paced recording on the right and the original morphology on the left indicates a prime target for successful ablation.

          All outflow track PVC's will have strong positive deflections in leads II, III and aVF. To distinguish if the origin is right or left, look to the precordial leads V1 - V3.

        The LVOT lies posterior to the RVOT. To reach the positive electrodes of the first three precordial leads, the electrical wavefront must travel a greater distance from the LVOT than it would if it originated from the RVOT. This extra distance causes an R wave to appear in V1 or V2. The more pronounced the R wave in these leads, the more posterior the origin lies.

          This image shows the complete endocardial surface of the heart. The blue right ventricle is the most anterior structure in the heart. The outflow track connects the main chamber of the right ventricle to the Pulmonary Artery (PA).

          The left ventricle is shown in red and lies posterior to the right ventricle. The LVOT is tucked in behind the RVOT. Thus, the wave front of depolarization from beats originating in the LVOT must travel further to reach leads V1 and V2. This is what causes the positvie deflection in these leads..

          Here is an alternate look at the right and left ventricular outflow tracks. In this image, the right atrium is no longer visible allowing the viewer unobstructed look of the relationship of the RVOT and LVOT.

          Note how the RVOT is anterior to the LVOT. When performing an outflow track case where there is any indication of LVOT possabile origin such as small R waves in V1 or V2, consider using unipolar EGM's to map the AO valve annulus. This is especially true when the earliest activation is found in the posterior septal aspect of the RVOT.

          This image is useful in helping to visualize how much further an electrical wave front (orange arrow) would have to travel to reach the anterior location of the early precordial leads.