• cerebral embolic lesion incidence [ Time Frame: on day 1 post-ablation ]
  incidence of new cerebral embolic lesions measured by magnetic resonance imaging (MRI) post-ablation as compared to pre-ablation imaging studies
• overall neurocognitive function, change [ Time Frame: from baseline (pre-ablation) to 6 months post-ablation ]
  percent change in overall neurocognitive function score from baseline (pre-ablation). The neurocognitive function examination includes items from the Brain Health Assessment, a validated, multi-domain testing battery aims to detect cognitive impairment in older adults. The TRAVERSE Testing Battery will include the following tests: Favorites (Forms A and B), Match (Forms A and B), Favorites Delay (Forms A and B), Favorites Recognition (Forms A and B), Dot Counting (Forms A and B), Flanker, and Running Dots.

• new cerebral embolic lesions, number [ Time Frame: on day 1 post-ablation ]
  number of new cerebral embolic lesions per person, measured by magnetic resonance imaging (MRI) post-ablation as compared to pre-ablation imaging studies
• complications related to the ablation procedure, rate [ Time Frame: post-ablation, through Month 6 ]
  rate of complications related to the ablation procedure
• symptoms specific to VT/ PVC, change [ Time Frame: from pre-ablation to post-ablation, through Month 6 ]
  change in self-reported symptoms specific to VT/ PVC
• quality of life composite score, change [ Time Frame: from baseline (pre-ablation) to 6 months post-ablation ]
  change in quality of life score (composite summary points) measured using the Short Form 12-item Survey (SF-12), a validated measure of health status.
• physical activity (MET-min/week), change [ Time Frame: from baseline (pre-ablation) to 6 months post-ablation ]
  change in total physical activity (MET-min/week) measured using the International Physical Activity Questionnaire (IPAQ) short format questionnaire, validated for physical activity-related energy expenditure.
• recurrent arrhythmias, rate [ Time Frame: at 6 months post-ablation ]
  rate of recurrent arrhythmias determined as part of routine clinical care, measured using ECG and continuous ECG monitoring, if data is available

• Procedure: Transseptal Aortic Approach Catheter Ablation Procedure
  The transseptal approach entails obtaining femoral venous access, and, guided by fluoroscopy and intra-cardiac ultrasound, starting with a transseptal needle or RF device inside the dilator of a long sheath; pulling down until the fossa ovalis in the interatrial septum is engaged on both fluoroscopy and intracardiac echo imaging; once on the left side, the long sheath is advanced over the transseptal needle, the needle and dilator are removed, and the ablation catheter can then be advanced across the mitral valve into the left ventricle.
• Procedure: Retrograde Aortic Approach Catheter Ablation Procedure
  The retrograde aortic approach entails obtaining femoral arterial access and leaving a sheath in the femoral artery. Under fluoroscopy, an ablation catheter is then advanced up the ascending aorta where the catheter tip is curved using an internal mechanism controlled on the handle of the catheter to form a large loop (to prevent the tip from traveling down a coronary artery and causing trauma such as a dissection); the curved loop is advanced around the aortic arch and down the ascending aorta. To cross the aortic valve with this loop, the catheter is typically torqued in various directions until it falls through the aortic valve and into the left ventricle.

• Active Comparator: Transseptal Group
  Transseptal Aortic Approach Catheter Ablation Procedure
  Intervention: Procedure: Transseptal Aortic Approach Catheter Ablation Procedure
• Active Comparator: Retrograde Group
  Retrograde Aortic Approach Catheter Ablation Procedure
  Intervention: Procedure: Retrograde Aortic Approach Catheter Ablation Procedure

Inclusion Criteria:

1. Men and women ≥ 18 years of age
2. Planned/scheduled endocardial ventricular tachycardia (VT) or premature ventricular contraction (PVC) catheter ablation procedure
3. For this patient, the current plan of the operator must be to pursue a catheter ablation target in the left ventricular endocardium that can be accessed by either a transseptal puncture or retrograde aortic approach
4. Life expectancy of at least 1 year
5. Willing and able to undergo pre- and post-ablation MRIs
6. Willing and able to return and comply with scheduled follow up visits (through the 6 month follow-up)
7. Willing and able to provide written informed consent

Exclusion Criteria:

1. Planned epicardial ablation that would include a coronary angiogram (during the index ventricular tachycardia (VT) or premature ventricular contraction (PVC) catheter ablation procedure)
2. Any contraindication to MRI (as defined by the institution performing the MRI)

3. Clinical contraindication to a retrograde aortic approach as determined by the treating physician, including:

   1. Severe Aortic stenosis
   2. Mechanical aortic valve

4. Clinical contraindication to a transseptal puncture as determined by the treating physician , including:

   1. Severe Mitral valve stenosis
   2. Mechanical Mitral valve
   3. ASD or PFO closure device that would preclude a transseptal puncture
   4. Mitraclip or Alfieri mitral valve repair that would preclude a transseptal puncture
5. Planned or known need to perform either a retrograde aortic approach or transseptal approach (such as to target another site during the same procedure)
6. Inability to speak, read, and write in the English language at a 6th grade level (required for the Neurocognitive Function Testing)
7. Current mental impairment or other diagnosis which precludes accurate assessment of neurocognitive function or which may not allow patient to understand the nature, significance and scope of the study
8. Inability to perform neurocognitive function testing after > 24 hours free of sedating medications