Hi @npfl, and welcome to Mayo Clinic Connect.
I learned something from you! I had no idea 10-12% of HCM patients end up with pacemakers!
I hope somebody from our little group can answer your question...in the meantime, has your care team referred you to Mayo in Jacksonville? Have they indicated this rapid progression of your heart conduction is related to HCM or is it in addition?

I found this online, but I am not sure it the same situation as yours:

Search Assist

Rapid progression of conduction disorders in the heart, affecting both the atrioventricular (AV) and sinoatrial (SA) nodes, can lead to serious arrhythmias and may result in symptoms like dizziness, fainting, or even heart failure. It is crucial to seek medical evaluation and treatment if such symptoms occur, as these conditions can be life-threatening.
Merck Manuals National Institutes of Health

Overview of Conduction Disorders
Conduction disorders affect the heart's electrical system, which controls the heartbeat. The two main types are:

Atrioventricular (AV) Block: This occurs when the electrical signals between the atria and ventricles are delayed or blocked.
Sinoatrial (SA) Node Dysfunction: This involves issues with the heart's natural pacemaker, which can lead to irregular heart rates.
Symptoms of Conduction Disorders
Symptoms can vary widely, but common signs include:

Slow or fast heart rate
Heart palpitations
Dizziness or lightheadedness
Extreme tiredness
Fainting
Shortness of breath
Chest pain or discomfort
Diagnosis and Progression
Diagnosis typically involves:

Medical History: Understanding symptoms and family history.
Physical Exam: Checking for signs of heart issues.
Tests: Electrocardiograms (EKGs) and possibly genetic testing.
Conduction disorders can progress rapidly, especially in cases of AV block or SA node dysfunction. Factors influencing progression include:

Age: Older adults are more susceptible to these disorders.
Genetics: Some conditions, like Brugada syndrome, are hereditary and can worsen over time.
Underlying Health Issues: Conditions such as heart disease can exacerbate conduction problems.
Management
Management strategies may include:

Monitoring: Regular check-ups to track heart function.
Medications: To manage symptoms or underlying conditions.
Pacemaker: In severe cases, a pacemaker may be needed to regulate heart rhythm.
Understanding these aspects can help in recognizing and managing conduction disorders effectively.

National Institutes of Health
Wikipedia
How are you feeling? When is your next appointment?

My heart-block situation sounds less complicated than yours, npfl, but some readers may find my story instructive.

I was advised before my septal myectomy and mitral valve repair surgery in July that in about 5 to 8 percent of septal myectomies, the surgery itself causes heart block because the cutting of the heart muscle interrupts neural/electrical pathways that control the heartbeat.

Turns our I am among that 5-8%. My post-op heart rate slowed to about 40 beats or less per minute, so 4 days after surgery a pacemaker was installed. My resting heart rate with the pacemaker is now in the low 70s. I was not told the specific type of heart block I experienced but from my online (amateur) research it seems like the AV type.

The pacemaker sends data daily to a computer. After about a week I was told the pacemaker was detecting atrial fibrillation so I am now taking a blood thinner, apixaban (brand name Eliquis), to protect against blood clots. (I do not feel any symptoms from the a-fib.)

The docs and I will see whether the a-fib resolves itself in the next few months, in which case I may be able to discontinue the apixaban.

Good luck addressing your issues, npfl; maybe someone on here has had a similar experience.

@baystater101 wrote a detailed and understandable explanation about ICDs after a septal myectomy. After my septal myectomy in 7/22, I did not need an ICD. It was probably around 2 or 3 weeks later that I began experiencing times of dizziness and giddiness (I felt like I was being lifted up), when moving around. My cardiologist and colleagues could not find anything - well - looking back on it, I should have had a modified stress test just to see what was going on. After a syncope 10/22 I wore a Holter for a month, I had to press a button each time I was dizzy. before the results came back, I had another syncope. Once the results were in, it was apparent that I was experiencing arrythmias! It was a great day when my ICD was installed - no further dizziness again. Hearts undergo trauma during surgery and then heal; there is scar tissue which can interfere with the electrical functioning. I told my cardiologist that I think I should have had a Holter after a couple of weeks of dizziness, his response was that they are obliged to follow protocol, upon examination, one was not warranted. He is well versed in HCM and one to consult with colleagues and medical literature - I hope everyone learned something here from my experience. It was NOT FUN!