Hypertrophic cardiomyopathy (HCM) is a relatively common genetic disorder that presents with ventricular hypertrophy caused by non-systemic or cardiac factors. It occurs in all ethnic groups and in similar proportions in both sexes. In recent years, treatment of symptomatic hypertrophic obstructive cardiomyopathy (HOCM) patients with percutaneous septal myocardial chemical ablation (PTSMA) has been shown to reduce symptoms and improve function and quality of life. Yuan Jiansong, Department of Cardiovascular Medicine, Fu Wai Hospital, Beijing, China
1. Left ventricular outflow tract (LVOT) obstruction
Hypertrophic myocardium divides the left ventricular cavity into a high-pressure zone at the left ventricular apex and a low-pressure zone under the aortic valve. The two form a pressure step difference (PG). Outflow tract obstruction varies widely, and it is now generally accepted that left ventricular outflow tract pressure step difference (LVOTPG) is an important indicator of clinical course. Hypertrophic obstructive cardiomyopathy HOCM has an annual mortality rate of 2-4% and an incidence of sudden death of ≤1%.
2. Percutaneous septal chemical ablation (PTSMA)
The mechanism is to ablate the hypertrophic septum by chemical means, resulting in widening of the left ventricular outflow tract, reduction of cardiac afterload, and increase in cardiac output. In 1995, British physician Sigwart first reported in Lancet the successful treatment of hypertrophic cardiomyopathy by applying 96% alcohol to obstruct septal branches.
2.1 Indications for PTSMA
Clinical indications: (1) Clinically suitable for patients with symptoms despite drug therapy, poor drug therapy or severe side effects, and cardiac function classification ≥ NYHA III/CCS III. (2) Patients with high pressure step difference and high risk factors for sudden death or objectively limited NYHA class II, or with exercise-induced syncope, or reduced mobility, despite their symptoms are not severe. (3) Failure of the original surgical resection or implantation of a DDD pacemaker. (4) Some patients have comorbidities that increase the risk of surgical procedures. Hemodynamic indications in symptomatic patients: LVOTPG > 50 mmHg at rest or inspired LVOTPG > 100 mmHg. Morphologic indications: Ultrasound demonstrates subaortic hypertrophy with SAM-related pressure gradients and midventricular gradients, and papillary muscle involvement and mitral leaflet overgrowth should be excluded. Coronary angiography has appropriate septal branches. At the 2008 European Annual Congress of Cardiology, the renowned German physician Seggewise concluded that a LV pressure step difference >30 mmHg at rest or a stimulated LV pressure step difference >60 mmHg could be an indication for PTSMA.
2.2 Non-indications for PTSMA
(1) Non-obstructive hypertrophic cardiomyopathy. (2) Combined diseases that necessitate cardiac surgery, such as severe mitral valve lesions and triple branch coronary artery lesions. (3) No or only mild clinical symptoms, even if LVOTPG is high, should not be done. (4) The target septal branch cannot be identified or the balloon is not exactly fixed in the septal branch. Although there is no restriction on age, in principle, caution should be exercised in young and elderly patients.
2.3 PTSMA operation technique
The key to the technique is to identify the target septal branch to achieve good hemodynamic improvement while minimizing complications. A temporary pacemaker must be inserted; aortic and left ventricular pressures must be monitored at the same time to exclude pressure gradients caused by valve disease. Preoperatively, 10,000 u of heparin is routinely administered at the Fu Wai Hospital.
The temporary pacing electrodes were implanted preoperatively, and the position and pacing heart rate were adjusted. A 0.014″ guidewire (most commonly used in BMV) is selected and delivered to the target septal branch, and a suitable over the wire balloon is delivered along the guidewire to the proximal segment of the target septal branch. After the balloon is inflated under pressure, the distribution of the septal branch is determined by injecting contrast or ultrasound foam (Levovist) through the central lumen. The contrast agent is observed to enter the anterior descending branch or other vessels through the collateral vessels, and the size of this septal branch distribution area is observed with the ultrasound probe. If contrast is observed on ultrasound to be distributed elsewhere in the posterior ventricular wall of the papillary muscle, alcohol should not be injected. The change in pressure step difference should also be observed during the pressurization of the balloon, and if the pressure step difference decreases by ≥50% or more, anhydrous alcohol injection can be considered. The selection of the ablation area is crucial, especially in those with unclear septal branches of the target vessel, the size and distribution of the first septal branch are highly variable. 20% of patients have the first septal branch supplying the free wall of the right ventricle; 40% of patients have the subvalvular septum not completely supplied by the first septal branch. 5% of patients cannot determine the target septal area. Morphine 3mg is routinely given before anhydrous alcohol injection; the amount of anhydrous alcohol injected is based on the acute hemodynamic effects, the size of the septal branch distribution estimated by ultrasound, and close observation of chest pain and arrhythmias. in principle, as long as the therapeutic effect is achieved, the amount of alcohol should be reduced as much as possible, and the less it is, the less likely complications will occur. The dosage of alcohol is usually 0.5-2.5 ml, and the process of alcohol injection must be carried out under fluoroscopy to observe the balloon filling and the presence of heterotopia. The pressure on the pressure gauge should be closely monitored. Finally, imaging should be performed to determine the presence of coronary artery injury and septal branch obstruction as well as coronary flow status.
The ablation endpoint is a ≥50% decrease in LVOTPG. If there is non-recovery of III° AVB, a DDD pacemaker may be implanted. Myocardial acoustic imaging can significantly reduce PTSMA complications and avoid false ablation. If the symptoms recur after PTSMA and the pressure difference returns, PTSMA can be performed again, but it should be performed three months after the first PTSMA.
3. Clinical efficacy of PTSMA
From December 2000 to August 2008, a total of 106 patients underwent PTSMA at Fu Wai Cardiovascular Hospital, with a successful intervention rate of 81.1%. Two patients (1.89%) died in-hospital, one due to alcohol flow through the traffic branch into the anterior descending branch and right coronary artery, and the other due to pharmacological hepatic necrosis caused by antiarrhythmic drugs. one patient (0.94%) had intraoperative ventricular fibrillation but recovered well after surgery. 55 patients (51.89%) had transient III° AVB, and only one patient had a permanent pacemaker. two patients PTSMA again.
4. Complications of PTSMA
(1) In-hospital mortality in 2-4%. (2) High or III° AVB requiring a permanent pacemaker: 2-10%. Influencing factors: whether to apply myocardial acoustic imaging method. Amount and rate of alcohol. (3) Bundle branch block: about 50%, predominantly right bundle branch. (4) Non-therapeutic myocardial infarction: anterior descending branch tear, alcohol leak, no reflow due to improper injection site, left anterior descending branch or left main stem injury. (5) Emergency surgical procedures: causes: coronary artery injury, acute mitral valve closure insufficiency.
5. Follow-up
PTSMA-treated patients have been followed for up to six years, and the technique was found not to increase the risk of sudden death or arrhythmias. There were no cases of ventricular septal perforation. A significant and sustained decrease in left ventricular outflow tract pressure gradient was an important feature. 56% of patients had a further decrease in resting and excitation pressure gradient at 3 months compared to the acute phase; 43% had a further decrease at 1 year compared to 3 months. 40% of patients had a complete decrease in pressure gradient at 3 months, and this value increased to 62% at 1 year. 90% of patients had a complete elimination of pressure gradient at 43 months. After 43 months, 90% of patients had a complete elimination of the pressure step difference. There was a significant improvement in symptoms and mobility.
6. Disadvantages and limitations of PTSMA
If injury to the left coronary artery requires emergency bypass or stent placement, sometimes the balloon cannot enter the target septal branch. Sometimes the target septal branch cannot be identified. Some young patients have unsatisfactory results of pressure step reduction. Possible reasons: good collateral circulation in the septum; higher degree of septal hypertrophy, higher degree of fibrosis, and poorer scar formation after septal ablation.
Summary
PTSMA treatment in some selected patients with HOCM can achieve clinical symptoms and hemodynamic improvement. Due to the possibility of early and long-term complications, strict and careful patient selection, close intraoperative and postoperative monitoring, and regular follow-up are advisable.