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br Case At the time of admission the
Case
At the time of admission, the patient\'s heart rate was irregular with an average rate of 76beats per minute (bpm) (Fig. 1). Her ECG showed sinus rhythm conducted with left-bundle branch block (LBBB) and associated with multiple ectopic premature ventricular beats (PVBs). The PVBs were relatively narrow, with a negative QS morphology in lead V1 but a positive QRS morphology in lead I, V2 and V3. Overall, these PVBs exhibited a left intraventricular conduction delay morphology of probable septal origin and most likely due out to breakout toward the RV. Measured in lead II, sinus beat QT interval was 400ms and corrected QT (QTc) interval for its preceding RR interval was 447ms. Following intermittent spontaneous PVBs, the QT interval remained 400ms and QTc value for the RR interval following the compensatory pause was 373ms respectively.
The AECG monitor revealed a one-minute episode of sustained polymorphic ventricular tachycardia at 200bpm (Fig. 2). The onset of the tachyarrhythmia was associated with a ‘long-short sequence’ characteristic of torsades de pointes, but in the absence of evident QT interval prolongation. The PVB triggering the tachycardia (Fig. 2) was different than was recorded on the baseline ECG, but unfortunately was not captured on a 12-lead a recording. The timing of the tachycardia correlated with the most recent loss of consciousness episode. The AECG recording was marked by very frequent PVBs (8% of the total beat count), some occurring in bigeminal cycles associated with diary entries indicating “lightheadedness”.
Trans-thoracic echocardiography revealed a left ventricular ejection fraction (EF) estimated at 32%, left ventricle dysynchrony (likely due, in part, to abnormal septal motion from the LBBB), and a hyper-trabeculated left ventricle compatible with non-compaction cardiomyopathy. A subsequent ECG-gated cardiac MRI (Fig. 3) without and with intravenous tetramisole revealed a borderline dilated left ventricle with an internal diameter in diastole (LVIDd) of 60mm, and hyper-trabeculations especially in the lateral, anterior and apical walls. The non-compacted myocardium to compacted myocardium ratio was greater than “2”, meeting the criteria for isolated left ventricular non-compaction.
In the 4 months following the ICD implant, the device recorded numerous PVBs, as well as non-sustained and sustained polymorphic ventricular tachycardia episodes at 280–333bpm and associated with a long-short initiation sequence. The sustained tachyarrhythmic episodes were terminated by ICD shocks at 35J (Fig. 4). To decrease the incidence of these episodes, the ICD lower pacing rate was increased from 70 to 80bpm and beta-adrenergic blocker therapy was initiated.
Discussion
Isolated LVNC is a primary genetic cardiomyopathy with either a sporadic or familial transmission often associated with neuromuscular disorders or musculoskeletal abnormalities [10]. In this case, there was no evidence of associated neuromuscular disease.
The association of LVNC with ventricular tachycardia (VT) is well know but its reported incidence varies. Oechslin et al. [8] described VT occurrence in 41% (14 patients out of 34 cases of LVNC), mostly non-sustained VT. Only 3 out of 14 patients had sustained VT and received an ICD. Conversely, Lofiego et al. [11] followed 65 patients with LVNC, and reported sustained VT incidence of only 6%. Just 9% of this study population underwent ICD implant. Fazio et al. [7] followed 238 patients with isolated LVNC with periodic Holter monitoring every 6 months for 4 years; 11 patients (4.2%) had documented VT, but sustained VT episodes were present in only 2 cases.
Currently, the mechanism underlying ventricular tachyarrhythmias in LVNC is not understood. There is MRI and positron emission evidence of perfusion defects in the areas of non-compaction [12]. The underlying mechanism may be a failure of the coronary microcirculation to grow with the increase of the ventricular mass. Junga et al. [13] described the presence of late potentials or prolonged QT dispersion in some cases, a potential marker of increased risk of sudden cardiac death or sustained VT.