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Ventricular Tachycardias - Outflow Track Tachycardias


Usually focal in nature.

May be an indicator of early stages of ARVD.

Activation is high to low as shown in the inferior leads.

Transition of the precordial leads helps to determine RVOT vs LVOT origins.

Chart for different locations

A Look at RVOT VT

          The following images were collected from one procedure. The images selected provide some valuable insight to RVOT arrhythmias. To the right of each image is an explanation of what the image displays and what role the information displayed plays in the overall procedure. Note that the first image is a standard surface 12 lead recording. When ectopy presents itself at the start of any procedure, it is important to record a 12 lead. Many times it is difficult to reproduce focal arrhythmias in the lab once a patient is supine or sedated. If you have a 12 lead recording based upon the lead placement within the lab, then you can always resort to pacemapping if the rhythm is not induceable once the procedure starts.

          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.

          As the case progresses, the ablation catheter is moved closer to the area where the origin is believed to be based upon the surface ECG. In essence, this is an early form of intracardiac mapping. By comparing timing on the onset of the surface QRS, it is easy to see that the RF distal catheter starts later than the onset of surface. We know that the catheter is not yet in position for ablation. If this were a good target for ablation, the onset of the RF signal should preceed the onset of surface QRS by around 30ms.

          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.


A Look to the Left.... (LVOT)

            Now that we know how to identify RVOT origins of PVC's / VT, let us compare this to the morphology of ectopics that originate from the Left Ventricular Outflow Track.

          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.


The images above provide a good look at some of the events and techniques used in outflow track mapping. Some of the key points to take away from this page are as follows;

  1. Both the RVOT and LVOT are located high in the heart.
  2. Outflow track tachycardias are identified by the significant high to low activation as visualized in the inferior leads.
  3. The RVOT lies anterior to the LVOT.
  4. The difference between RVOT and LVOT may often be determined by looking at the R wave transition in the precordial leads. A transition to a positive R wave in V1 or V2 is often indicative of LVOT origin. A transition in V3 or later is indicative of RVOT origins.
  5. As outflow track tachycardias are almost always focal in nature, keep an eye out for the cycle length ramping up or ramping down.
  6. Remember it is always a good idea to have an art line for these cases.
  7. In any procedure it is possible to "bump" the endocardium and generate a "false" ectopic. Identify these by differences in timing and morphology.
  8. Pacemapping provides a good tool to help verify if the location you are at may represent a viable ablation target.


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