The incidence of hypertrophic obstructive cardiomyopathy (HOCM) is known to be about 0.2%, while recently a few researches revealed that it could be higher . The hypertrophy of septum and the anterior wall, mitral valve systolic anterior motion constitute the left ventricular outflow tract (LVOT) obstruction. In the circumstance of drug refractory, non-pharmacological should be taken into account. Currently, there are two non-pharmacological treatments: ventricular septal myectomy and alcohol septal ablation (ASA). Although ventricular septal myectomy is the gold standard for the treatment of HOCM , the availability of high-quality operation is limited, which could not cope with the relatively high prevalence of HOCM . As the secondary therapy for HOCM, ASA is mini-invasive, but it relies on individual anatomy of septal arteries. So about 1%-15% of the patients could not be the candidates of ASA [4,5]. Both of the former mentioned treatments have the risk of complete atrial-ventricular block, which call for the pacemaker therapy. Endocardial radiofrequency ablation of septal hypertrophy (ERASH) has been applied on HOCM since 2004, by Dr.LAWRENZ . No matter where the hypertrophy is located, the transcatheter approach enables ablation of endocardium, with multiple lesion up to 28mm , imitating the effect of ventricular septal myectomy. Although the experience with ERASH so far always encountered with residual gradient, the developments of the symptoms do exist. We reported ERASH applied in two people with HOCM.
A 66-year old man suffered from symptom of HOCM (activity related chest tightness, shortness of breath, NYHA II-III, angina CCS II) with sign of left ventricular hypertrophy on electrocardiogram and elevation of troponin T and BNP. He was admitted to our center without treatment. Transthoracic echocardiography (TTE) (vivid I, General Electrics and IE33,Philips) revealed an unsymmetrical hypertrophy of left ventricle, with posterior wall/interventricular septum thickness 20mm/12mm, accompanied with systolic mitral valve systolic anterior motion (SAM) (figure 1A), and gradient of LVOT at admission was 60mmHg at rest by continuous-wave doppler (figure 1B). Coronary angiography was performed to rule out the possibility of coronary artery disease, and sought for suitable septal artery, which turned out to fail. After prescribed the dosage of 47.5mg metoprolol, the patient’s heart rate was controlled on average of 68bpm. The gradient at rest and the sign of SAM vanished. But the shortness of breath and activity related chest pain still remained. A provoked gradient was suspected. Thus, a pharmacological stress echocardiography and invasive measurement were under consideration.
Stress echocardiography and invasive measurement:
At the beginning of the procedure, a 5Fr MP catheter was introduced into the left ventricle through the right femoral artery. An invasive radial pressure was acquired by invasive blood pressure monitor. The gradient between peak left ventricular pressure and radial pressure remained less than 30mmHg (figure 2A). And then, dobutamine at the velocity of 5ug/kg·min-1 was given by micropump to stimulate the gradient. But due to the effect of metoprolol, the heart rate responded less sensitively than the blood pressure. So even when the blood pressure reached 200/80mnHg, the heart rate remained approximately 62bpm. Until then, the gradient remained unchanged. For the grant of safety, dobutamine was terminated. Taking into consideration that the gradient of LVOT in HOCM is closely related with heart rate, the isoprenaline was pumped in at 0.2ug/kg·min-1 to activate the β1 receptor. The heart rate quickly reached 87bpm, but the radial blood pressure dropped to 78/39mmHg. The isoprenaline was terminated promptly. The highest gradient measured by TTE was 237mmHg at the heart rate of 87bpm (figure 2B). In the meantime, the SAM turned to be positive, as well as the regurgitation of mitral valve graded to be moderate. The systolic mitral valve attached area was targeted to be the ablation area.
A 6Fr pacing catheter was inserted through the right femoral vain into the right ventricle if necessary. The probe of intracardial echocardiography (ICE) (12Fr, SOUNDSTAR, Johnson & Johnson Medical) passed through the opposite femoral vain into the right ventricle to display the LVOT and constructed a three-dimension model of left ventricle. Firstly, a retrograde transaortic way was attempted to place the ablation catheter (8Fr, Biosense Webster) to the targeted area (figure 4). But due to the impossibility to make the catheter stably adhere to the hypertrophic septum, a trans-atrial access was adopted, assisted by a steerable sheath (Agilis, St.Jude). A dose of 4000IU heparin was administered intravenously to maintain the activated clotting time. The ablation catheter was guided by the ICE and fluoroscopy to the constructive LVOT. To prevent injuring the His bundle and the left bundle branch, intracardial potential was detected before ablation by Carto 3 mapping system (Biosense Webster). The ablation generator (Stockert GmbH, Biosense Webster) was applied to deliver 40w for 60s every time. The cooling pump was programmed to release saline 30ml/min during ablation (Thermocool, Biosense Webster). A series of 7 radiofrequency lesions (total time of radiofrequency application, 4.9 minutes; energy range, 40 W; temperature range, 30-35 °C; contacting pressure, 20-35 g) were delivered in the region of the septal bulge about 1.6cm2(Figure 3). Finally, the stress echocardiography was repeated, and gradient declined to 83mmHg at the heart rate of 88 bpm (figure 2C)，and the blood pressure remained 151/68mmHg at the heart rate of 153bpm. The patient finished the operation with a slight prolongation of QRS to 120ms, with incomplete left bundle branch block, without the complication of cardiac effusion and complete atrioventricular block. The fluoroscopic time was 12 min.
After the operation, the patient went through the surveillance of electrocardiogram monitor. None of fatal arrythmia was documented. Nor did the patient feel any discomfort. 48 hours after the operation, the patient got discharged. After one month of the ERASH, the patient felt angina disappeared. Electrocardiograph showed left bundle branch block diminished with QRS recovery to 100ms. There was an echo-enhanced region notice at the place of ablation through TTE（Figure 5A）.The thickness of the myocardium did not change too much. The stress echocardiography presented a gradient at rest of 26mmHg (HR 78bpm) (figure 5B), with SAM negative, without mitral regurgitation, a gradient at provocation of 166mmHg (HR 106 bpm) (figure 5C) and 25mmHg (HR 88bpm) (figure 5D), with SAM positive and mitral regurgitation. The blood pressure fluctuated between 135-158/75-85mmHg.
A 30-year-old woman, presented with shortness of breath for 7 years, exacerbation after activity, was diagnosed with HOCM by echocardiography. The maximum septum was 24mm, and mitral valve moved towards the septum during systole. The gradient of LVOT measured by doppler was 146mmHg. Mitral regurgitation graded to be mild to moderate. After the coronary angiography, proper septal artery was not found. So ERASH was performed as described above through a retrograde transaortic pathway. The target region was the SAM area. The radiofrequency time was 22.4 minutes, energy released was 40 W per 60s, and contacting pressure was 5-15g. Since the region of His bundle was too abundant, coinciding with the region of SAM area, the ablation area was not enlarged. Right after the operation, the gradient fell to 115mmHg. The patient discharged 5 days after the operation. The patient felt relief at rest but the exercise tolerance did not change too much in a one-month follow-up. The TTE showed that the gradient decreased to 70mmHg, still with SAM positive and mild to moderate mitral regurgitation. At the site of RF current application, we noticed an enhanced area about 4mm thick.