The impact of coronary chronic total occlusion percutaneous coronary intervention on culprit vessel physiology

Background
Coronary chronic total occlusions (CTOs) are defined as an occluded coronary
vessel with (TIMI) grade flow 0 and a definite or an estimated duration of at
least 3 months . They are frequently encountered in patients undergoing
coronary angiography, and contemporary registries have demonstrated a
prevalence of approximately 25% in patients with obstructive coronary artery
disease .

Percutaneous recanalization of a CTO is challenging due to factors as the
chronicity of the occlusion, the length of the occluded segment and the
difficult visualisation distally to the occluded segment. For the above reasons
in the past, interventional cardiologists were reluctant to tackle CTOs. It is
characteristic that in the landmark SYNTAX trial , the incidence of a CTO was
double in the subjects with incomplete revascularisation in the PCI arm
compared to the ones with complete revascularisation . Furthermore when
attempted the procedural success was low compared to non-CTO PCI .

However, contemporary techniques and equipment lead to a high procedural
success and low adverse events rates in experienced centres. The hybrid
algorithm has incorporated dissection re-entry techniques (antegrade or
retrograde) as planned steps of the procedure that sometimes can be the
first/preferred choice. Using these methods, success rates of at least 80% are
now common when undertaking CTO PCI and complication rates resemble standard
PCI 9.

Rationale
Although, procedural success rate in expert centres is approaching the one of
non-CTO PCI long-term outcomes are not as good as with conventional
angioplasty. For example, contemporary registries showed increased rates of TVR
at one year and there have been no reproducible data supporting a reduction in
MACE. Thus, the focus has shifted in optimising long-term term outcomes and
ways to achieve that should be identified. The use of IVUS/OCT has been shown
to improve long-term outcomes in conventional angioplasty procedures . However,
recovery of blood flow and restoration of vasomotor tone will lead to vessel
remodeling with significant lumen and vessel enlargement weeks or months after
the index procedure. Studies using OCT at short term follow up in conventional
angioplasty have shown high rates of stent strut mal-apposition and incomplete
stent strut coverage . This highlights the unique challenges associated with
stent implantation in CTO vessels.

Fractional Flow Reserve is a validated tool to assess physiological severity of
coronary artery disease and the need for subsequent percutaneous
revascularisation. Recent studies have shown that FFR measurements have a
prognostic role even after PCI. A cut-off point of 0.90-0.93 has been suggested
to correlate with better outcomes.

The aim of the study is to document changes in CTO vessels physiology post PCI
and at 3 months follow up. We intend to look for correlations between
anatomical features identified with intravascular imaging and physiological
parameters, how these develop at follow up and how they relate to the
revascularization technique. These observations will help us to plan methods of
optimising CTO procedures and design randomised studies to test hypotheses
generated from our study observations.

The aim of the study is to document changes in CTO vessels physiology post PCI
and at 3 months follow up. We intend to look for correlations between
anatomical features identified with intravascular imaging and physiological
parameters, how these develop at follow up and how they relate to the
revascularization technique. These observations will help us to plan methods of
optimising CTO procedures and design randomised studies to test hypotheses
generated from our study observations.

Study outcome measures
1. To identify changes in coronary physiology (flow, pressure and resistance)
between index procedure and follow up.
2. To identify changes in anatomy between index procedure and follow up
3. To identify a relationship between anatomical/physiological measurements and
exercise indices
4. To identify a relationship between anatomical/physiological measurements and
quality of life

Prospective observational study

Risks of procedure
Patients will undergo the CTO PCI procedure in line with standard practice and
international guidelines. After successful stenting, research measurements of
anatomy and physiology. Follow up angiography will take place as a research
procedure (complication rate of 1/1000), unless this is clinically indicated by
the operator at the time of PCI.

Pressure wire risks
The measurement of physiological parameters requires passing a small pressure
measuring wire into the stented vessel with a complication rate of 1/1000.

Use of adenosine
The risk of using adenosine is usually very small. It is short acting and
pharmacological effect continues for 3-5 seconds after discontinuation of the
infusion. The effects of adenosine include bradycardia and hypotension. As
these patients will be stable elective patients, there should be very few
instances where adenosine use is contraindicated. In these cases, it will not
be given.

Use of additional contrast
FD-OCT measurements will require the use of a small volume additional
contrast. As patients with a significant burden of renal impairment would not
be enrolled, the risk of this additional contrast is unlikely to result in
contrast nephropathy.

Additional radiation exposure
Consultant Cardiologists involved in the study are acting as Radiation
Practitioners under the Ionising Radiation Medical Exposure Regulations (IRMER
2000).

Additional fluoroscopic time to place the pressure wire at the end of the case
is small/negligible and unlikely to make any measurable change in radiation
exposure.