Pacing Percentages

Pacing percentages

by AgentX86 - 2023-07-18 19:55:09

Welcome, unfortunately, to the electric hearts club. Ask anything, someone here has probably been in your exact shoes, may it be biological, technical, or emotional. We've been there.

These are next to useless numbers for us.  The important thing is how you feel. A beating heart is better than one that isn't. All it means, for you (AV block), is that your block is pretty constant and your pacemaker is a very good thing.

A lot of people here are RV paced 100% of the time.  I am, but have a CRT so there is little chance of "cardomyopathy" (enlagement of the heart).  It's not "atrophy", where the heart muscle would get smaller.  Rather, it's the opposite, though neither would be welcome.

The LV is sill pumping but it may not be in sync with the RV. Think of the heart as a water baloon. If you squeeze it on one side, it bulges out the other, then a second later squeeze it on that side and it expands out the top.  Squeezing out the top, in this analogy, is the blood being delivered to the body.

Now, think of the water baloon being squeezed on both sides simultaneously.  The baloon doesn't momentarily expand on one side, rather straight up to the top, pumping the blood immediately.

This happens with the heart, too, except that it's two baloons glued together. When the right side (RV) compresses, it presses into the left side (LV) before the left side contracts, pumping the blood to the body. This is an unnatural sequence that can cause problems. In a very high percentage of the cases, nothing bad happens. 

Your cardiologist simply wants to take an echo-cardiogram (ultrasound) of the heart, once a year, to make sure this is't happening. He measures the amonut of blood from the LV that pumps in each heartbeat. If there us a problem, it's slow to progress (don't worry about the year) and there are solutions, one being the CRT (Cardiac Resynchronizion Therapy) pacemaker.  It's the same thing as what you have now, except that another lead is put in the LV (behind, actually) and the two are timed so both sides of the beat together again.

AgentX86 Balloon

by Stache - 2023-07-18 21:08:19

I must admit, AgentX86 has been instrumental in helping me understand the functioning of the heart with the analogy of a balloon. As someone with 3rd degree heart block and 100% pacing, my work in aerospace as an A&P examiner has provided a unique perspective. In my teaching of Bernoulli's principle and Bernoulli's equation in fluid dynamics, I have come to realize that the same principles apply to our heart as it pumps blood from one chamber to the next and out into our body. AgentX is absolutely right when he emphasizes that as long as the heart keeps beating, that's all that matters.

I have faced mental challenges in dealing with being paced, but revisiting the Bernoulli law has helped me overcome them. It has been 2.5 years now, and I continue to study and learn something new every day. There is still much more for me to explore and understand about our hearts.

right ventricular pacing

by Gemita - 2023-07-19 02:22:20

JLDClancy, firstly, a warm welcome.

You may wish to read the attached abstract links on Right Ventricular (RV) pacing burden which you will need to copy and paste into your main browser to open.  Pacing induced cardiomyopathy (PICM) is defined as a drop in left ventricular ejection fraction (LVEF) due to a high amount of right ventricular (RV) pacing. Although PICM occurs with chronic, and occasionally, acute high burden of RV pacing, the minimum burden of RV pacing inducing PICM is not widely established.

You will see from the first link, a statistically significant decrease in left ventricular ejection fraction was found in patients with more than 40% right ventricular (RV) pacing, but not in patients with less than 40% RV pacing, suggesting that 40% of RV pacing is the likely threshold for producing left ventricular systolic dysfunction and cardiomyopathy.  It has to be said though that not all patients with a high burden of RV pacing will go on to experience a deterioration in their heart function since multiple risk factors for PICM have been found (see second abstract link).

Further my doctor told me that a susceptible patient would likely exhibit signs of loss of synchrony between the two ventricles at a very early stage in their pacing journey (say within the first few years of a high burden of RV pacing) when an upgrade of their pacing system would be offered.  If no early adverse effects were seen, it would likely never happen.

So the take home message is that if RV pacing can be controlled and kept low this would always be beneficial.  However, many members are pacemaker dependent and paced 100% in their RV and have been for years without any difficulty whatsoever.  Providing your doctors keep a close eye on things, you can stay safe.  Here in the UK, in my experience, CRT (cardiac resynchronization therapy) is not routinely offered to someone who is pacemaker dependent unless they show signs of heart failure or other difficult symptoms from a high burden of RV pacing.

I see from your % of RV pacing that your Mobitz block requires a high degree of pacing support to keep you comfortable and safe.  It would therefore be inappropriate to try to reduce the amount of your RV pacing (through settings changes) when you clearly need it.  Your doctor seems to be watching you carefully and will step in should you ever develop a problem.  Report any difficult symptoms promptly too is my best advice.  Good luck

https://www.ahajournals.org/doi/10.1161/circ.144.suppl_1.11902

https://pubmed.ncbi.nlm.nih.gov/34689900/

Gemita, AgentX86 & Stache

by Good Dog - 2023-07-19 10:00:08

There is little more that needs to be said to help answer TIA's (jldclancy) questions and concerns. I never fail to be amazed by Gemita. Her knowledge and the generosity she exhibits with the time she puts into helping others.  

I also have to say that Agent's explanation really struck me as being such a simple, but the most effective explanation I've read that really helps others to understand and grasp what is going-on when the RV and LV are out of sync and the cause of pacemaker syndrome. 

As someone that spent almost my entire career related to so many different aspects of fluid dynamics, Bernoulli's theorem is near and dear to my heart. It has helped me understand issues surrounding my heart in ways I hadn't realized or thought about until I read Stache's sentiments.

long term effects

by Tracey_E - 2023-07-19 11:18:42

I can't top Gemita and Agent's excellent explanations. A high pacing percentage and annual echo are perfectly normal for heart block. 

My ep told me the same as Gemita's told her. If the heart goes a few years paced with no effects on ejection fraction, odds are it will not happen later. I've paced every beat since 1994 and my EF has not changed at all, so my ep said he doesn't expect it to ever change due to pacing at this point. However, he still does an annual echo to keep an eye on things. 

The impact on the heart from not pacing would be much more dangerous than any potential side effects from pacing. 

The exception

by Good Dog - 2023-07-19 11:44:52

In light of Tracey's comment, I just want to say that apparently I am the exception to the rule. I have been paced for over 36 years. My EF did not drop significantly until sometime in the last 10 years. Unfortunately I did not have an echo every year as I should have (I went without one for the previous 10+ years), so I cannot say exactly when it dropped. However, I am very confident by the amount of the AV percent paced increase and my previous EF's that it happened gradually over the previous 10 years. My prior EF's were always 55%+. It is now 40% and my QRS interval is almost twice what it should be. Of course, I have an apical lead placement in the ventricle that certainly contributed to the problem. My recent echo reports very clearly state the fact that my LV is mishaped (a bit oblong) which is the result of the dyssynchrony and the decrease in EF. Actually, many years ago my pacer tech had told me that as I get older and have been paced for a very long time, the possibility of HF becomes much greater. At least in my case I think she was correct. Obviously EP's are much more aware these days of the importance of lead placement. So newer PM patients have the benefit of the knowledge and experience gained over time. Most are doing RV septal placement now or even better, HIS Bundle lead placement to avoid these issues.

Thanks everyone for the info

by Jldclancy - 2023-07-19 11:55:03

All of you are amazing - My cardiologist spent about 5 minutes with me for my annual checkup.  I just don't click with him so i'm going to try to find another doctor.

I have to read the comments a few more times to be able to understand all the new terminology that I'm not familiar with.

It's nice to know I'm right where I'm supposed to be and don't need to worry too much about cardiomyopathy