Hypertrophic cardiomyopathy (HCM) is the most common primary disorder of cardiac muscle. The incidence is about 1 in 500, which would mean 1.5 crore HCM patients will be living on our planet at any moment. The root cause of pathology is located in 20 odd genes that define cardiac muscle protein integrity. (Myosin, Troponin, Titin, etc) This leads to the bizarre architecture of cardiac muscle, prone to progressive fibrosis.(Paradoxically, 90% of HCM have normal or supernormal contractility till very late stages, proving that the much-dreaded term myocardial disarray has little effect on contractility. It is all the more funny, as we strive hard to suppress this excess contractility caused by disarray with beta-blockers.
SCD is the scary face of this disease. If the incidence of SCD is less than 1 % per year, do a little maths to know how many will succumb every year to this disease. However, It is the symptoms like exertional dyspnea (most common,) followed by syncope and rarely angina that bring HCM patients to the physician. Though the pathology is diffuse and global, I don’t understand why we got stuck with the outflow tract gradients and dynamic obstruction. HCM is an equally a disorder of LV inflow obstruction (rather a restriction). It can be presumed myocardial disarray makes more impact on diastole than systole. The relationship between inflow and outflow gradient is a poorly explored area in HCM. Detailed analysis of E and A velocity profiles along with tissue Dopper will throw more light in symptomatic patients.
The importance of LVOT gradient in HCM was questioned by Criley more than 30 years ago.
There may not be many takers for this concept in spite of our realization, that the major symptom of HOCM is not due to outflow tract obstruction. Further, sudden cardiac death risk is not fully negated by drugs and surgical myectomy. Christopher J. McLeod EHJ 2007) No surprises we require the help of ICD to tackle the SCD risk even after the relief of obstruction.
How to measure the gradient in HCM?
Image source: .Jeffrey B.Geske Assessment of Left Ventricular Outflow Gradient: Hypertrophic Cardiomyopathy Versus Aortic Valvular Stenosis JACC: Cardiovascular Interventions Volume 5, Issue 6, June 2012, Pages 675-681
- Continuous-wave Doppler is to be used for net LVOT gradient.
- Pulse doppler to analyze regional, local gradient profile within LV chambers
- HCM we need to follow up with peak gradient unlike valvular AS because unlike valvular AS gradient is not uniform to be differentiated for MR jet (Ref Jeffrey B.Geske Mayo clinic )
- The lobster claw pattern (M V Sherrid JASE 1997) is academically exciting, as it documents the sign of obstruction. (Please note, pulses bisferiens is clinical lobster claw bite, felt in the neck )
- This is the only entity “standing echo” to be done. compared to sitting and semi-supine position.(Stand echo is the simplest provocation )
- Chronic BB therapy does reduce the gradient.(There is some evidence, disopyramide beats BBs for this purpose )
- Associated systemic hypertension can influence the gradient in a complex manner(meaning either under overestimate )
How to provoke gradient if the resting gradient is low.
- Valsalva maneuver
- Post VPC
- Excercise
Dountaimine stress test should not be used as it can generate pseudo gradients. Should we provoke otherwise asymptomatic zero gradients healthy HCM? It is debatable and can be an unsolicited invitation to imaginary troubles.
Importance of MRI: Morphology can be more important than gradient
It has now become a dictum every patient of HCM must undergo MRI. This not only helps to define the morphology of LV, different subsets of HCM, and risk of SCD , it also guides the surgeon where exactly to resect, and how much mass of myocardium to be removed. MRI defines mitral valve anatomy more clearly and helps whether AMl plication is required or not in addition to myectomy.(Elongated bulky Mel is competing for space in the narrow corridor of LVOT, you know ) MRI clearly helps to avoid over-enthusiastic alcohol septal ablation as well.
Principles of management
- Symptom reduction, risk estimation, SCD risk reduction, and correcting associated arrhythmias like AF /VPDs, etc.
- Beta-blocker help relieves symptoms and control most VPDs or AF. No drug effectively eliminates the risk of SCD. (But, I doubt it’s wrong, BBs must have a positive impact on this we are failing to prove it ).
- ICDs are promoted as a mainstay to prevent SCD.It should be emphasized ICDs can’t reduce the troublesome exertional dyspnea of HCM.It simply prevents(expected to prevent ) SCD after allowing the VT/VF to occur. (ICD do come with its own morbidity and anxiety, Sub-cutaneous ICD is just beginning to be popular, doesn’t have VT control though no ATP algorithm )
- Surgery regresses LVOT gradient and regress symptoms still may be the best option (Dual-chamber pacing, alcohol ablation, (now RF) are mostly interventional excesses with unproven worthiness. Additional mitral valve repair strategy during myectomy has some proven value.
- Mavacamten (the proposed new magic drug ) is shown to steer and stabilize the two-headed myosin interaction with actin , thus reducing the force of contraction at the same time not inhibiting it truly. The mechanism is great on paper, let us see the follow up of EXPLORER study patients)
- Counseling & reassurance( The real risk of SCD is far less than the fear of SCD.I have seen the relatives of HCM patients are more worried than HCM patients with a 30mm IVS. This is amplified by a crazy battery of genetic tests with dubious predictive value. In my opinion, one need not do this even as the current guidelines trying hard to make it appear as a pleasant affair)
Final message
We are taught right from our early days in medical schools, HCM is synonymous with dynamic LVOT obstruction. However, to hang our thoughts exclusively on this hemodynamic concept lands us in management errors. Let us learn to look beyond LVOT gradients in HCM. We need to look at the overall morphology of LV, mitral valves, LA dynamics, etc. Please realize, there is a huge mass of myocardium sitting silently not eliciting any gradients, still good enough to cause symptoms and dictate the natural history.
Reference
Postamble
For the pure academics, please read this.The ultimate advisory from the authoritative source.
