Safety and efficacy of a low frame rate protocol for PCI for CTOs

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Safety and efficacy of a low frame rate protocol for percutaneous coronary intervention for chronic total occlusions

Chronic total occlusion (CTO)—a complete blockage of a coronary artery lasting more than 3 months—is a common yet challenging heart condition. While percutaneous coronary intervention (PCI) is a key treatment to restore blood flow, it exposes patients and cardiologists to higher radiation than non-CTO procedures. This is a critical concern: long-term radiation exposure is linked to health risks for both groups. Could a low frame rate (LFR) protocol reduce that radiation without hurting procedural success or safety? A 2021 study from Sichuan Provincial People’s Hospital explored this question.

Led by Ming-Huan Fu, Yuan-Yuan Pan, Xue-Fei Tao, Juan Du, and Biao Cheng (Department of Geriatric Cardiology, Sichuan Provincial People’s Hospital, University of Electronic Science and Technology of China), the research analyzed 110 CTO patients who underwent PCI between January 2017 and June 2019. Fifty-three patients were treated with an LFR protocol, while 57 followed the standard protocol. All CTOs were diagnosed by Biao Cheng, a Fellow of the American College of Cardiology (ACC), ensuring expert oversight.

What’s the Difference Between LFR and Standard PCI?

The LFR protocol was designed to cut radiation while maintaining image quality. Key changes from the standard protocol included:

  1. An extra 0.9 mm copper (Cu) filter for fluoroscopy (real-time X-ray guidance).
  2. Lower cineradiography (recorded X-ray videos) frame rate—from 15 to 7.5 frames per second (FPS).
  3. An extra 0.1 mm copper/1.0 mm aluminum (Al) filter for cineangiography (detailed blood vessel imaging).

Study Results: Radiation Reduction Without Compromising Outcomes

Demographically, the two groups were nearly identical. Most patients were men (83% in LFR vs. 81% in standard), and there were no significant differences in age, BMI, heart health metrics (like left ventricular ejection fraction), or CTO complexity (measured via the J-CTO score). The only notable gap: 3.5% of standard protocol patients were asymptomatic, vs. 1.9% in the LFR group.

When it came to the procedure itself:

  • Radiation exposure: The LFR protocol significantly lowered air kerma radiation (a measure of radiation absorbed by tissue)—4.3 Gy vs. 6.9 Gy in the standard group (P=0.010). It also cut radiation per minute by nearly half (75.8 mGy vs. 131.7 mGy, P=0.011). Electromagnetic radiation (another metric) was similar between groups.
  • Procedure metrics: Contrast dye use (327 mL vs. 308 mL), total procedure time (142 minutes vs. 138 minutes), and fluoroscopy time (57 minutes vs. 52 minutes) were all statistically similar.
  • Success and safety: Procedural success—defined as restoring normal blood flow (TIMI grade 3) with <30% residual stenosis and no in-hospital major adverse cardiac events (MACEs)—trended higher in the LFR group (7.5% vs. 5.3%, P=0.072). More importantly, the LFR group had a significantly lower rate of donor vessel dissection (9.4% vs. 10.5%, P=0.020)—a serious complication where the artery used to access the blockage tears. Other risks (like vessel perforation or cardiac tamponade) were similar between groups.

Why This Matters for CTO Patients and Doctors

CTO PCI is inherently higher-risk for radiation exposure than non-CTO procedures. The LFR protocol addresses this by balancing two critical factors: reducing radiation (protecting patients and clinicians) and maintaining image quality (ensuring the procedure is effective).

The study’s findings are promising:

  • Safer for patients: Lower radiation means fewer long-term risks, and a lower dissection rate reduces immediate complications.
  • No trade-offs: Key procedure metrics (time, contrast use) didn’t increase with LFR—so patients don’t face longer procedures or extra dye exposure.
  • Potential for broader use: While the study tested only one LFR protocol, it suggests that adjusting frame rates and filters can make PCI safer without sacrificing success.

Limitations to Consider

Like all research, this study has constraints:

  • Retrospective design: It looks back at past data, which can introduce sampling bias.
  • Small sample size: 110 patients is relatively small—larger, randomized trials are needed to confirm results.
  • Single protocol: Only one LFR approach was tested; other versions might yield different outcomes.

Conclusion

For CTO patients undergoing PCI, the LFR protocol appears to be a safe, effective way to reduce radiation exposure. It doesn’t compromise key procedural metrics and may lower the risk of serious complications like donor vessel dissection. As cardiologists work to make PCI safer, this study adds evidence that LFR could be a valuable tool.

Fu MH, Pan YY, Tao XF, Du J, Cheng B. Safety and efficacy of a low frame rate protocol for percutaneous coronary intervention for chronic total occlusions. Chinese Medical Journal 2021;134(10):1215–1217. doi:10.1097/CM9.0000000000001395

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