Electrocardiogram in apical hypertrophic cardiomyopathy with a speculation as to the mechanism of its features

Case #1 reveals that patients with AHCM are not immune to other illnesses such as atherosclerosis involving the coronary and peripheral arteries, and such comorbidities should be sought during the follow-up for AHCM. Patient #1 had comorbidities partially confounding the features of AHCM; however the influence, from the ECG point of view, of the features attributed to AHCM (enormous QRS, particularly R waves and large inverted T waves with specific three-dimensional orientation) were overwhelming. The mechanism of these two ECG features is attributed to the location of hypertrophy in patients with AHCM. Specifically, hypertrophy involving the left ventricular septal, anterior, lateral and inferior, midventricular, and/or basal territories is mitigated by cancellation of depolarisation forces generated by normal or hypertrophic regions; on the contrary, the apical distribution of hypertrophy in patients with AHCM opposite to the non-muscular elements of the fibrous cardiac skeleton of the mitral valve and annular plane provides the essentials for an unopposed expression of depolarisation vectorial forces directed towards the apex resulting in enormous R waves. The enormity of the R waves in patients with AHCM may also be related to histological changes (disarray of myofibrils and fibrosis) inherent to hypertrophic cardiomyopathy. Such changes may enhance the resistivity of the cardiac muscle which thus produces an increase in the amplitude of the R waves. A parallel which comes to mind is the frequent occurrence of very large R waves in glycogen storage disease type II, also known as Pompe disease or acid maltase deficiency, in which the large amplitude of R waves has been attributed to an increase in the resistivity of myocardial tissue due to accumulation of glycogen in the lysosomes and associated fibrosis. ST-segment and T-wave secondary changes usually mirror in extent the amplitude of QRS complexes and R waves in all forms of cardiac ventricular hypertrophy. Thus, it should be expected that the large R waves are associated with large secondary T-wave changes with opposite vectorial orientation, producing ‘giant’ T waves directed opposite the cardiac apex, i.e., superiorly, rightwards and posteriorly, as observed in these two patients with AHCM.

The ECG features of AHCM, which is the focus of this communication, are reported to be giant negative T waves [1, 2], ST depression and negative U waves in II, III, aVF, V4-V6, and a prolonged QTc [1]. However, giant negative T waves were not invariably seen in AHCM [2]. Also the depth of the negative T waves and ST-segment depression has been reported to vary from hour to hour, day to day, and year to year [1]. Others have described increased S-wave voltage in V1 + R-wave voltage in V5 up to 8.1 mV with inverted T waves, both of which either remained stable, or increased or decreased overtime in some patients [3, 4], or stable ECGs, increase or decrease by 10 mm or greater in the highest R-wave amplitude in the precordial leads, with newly developed giant T-wave inversion, or parallel changes in the negative T waves, or stable ECGs [5]. Newly developed LVH with giant T-wave inversion, and with lead V4 showing the tallest R wave have been observed [6]. The number of precordial leads with negative T waves (−0.5 mV or more) was greater in patients with AHCM with giant negative T waves (>1.0 mV) in the precordial leads; they were also found in more patients than in others, with different distribution of hypertrophy, and no upright (>1.0 mV) T waves in the precordial leads were found in patients with AHCM [7]. Patients with giant negative T-wave inversions (T wave >10 mm) and high R-wave voltages (R wave >25 mm) had more severe apical hypertrophy, although there was incomplete agreement between the ECHO and ECG, and at follow-up there was an increase in the negative T-wave amplitude, with parallel mild increase in the amplitude of R waves [8] Another study identified the mid-precordial leads in most of the patients as the ones revealing the ECG changes in AHCM [9]. Studies of Japanese patients with AHCM detected giant negative T waves and tall R waves in lead V5 or high S wave in V1 + R wave in V5 with a decrease in the amplitude of both at long-term follow-up [10, 11] The rare occasion of chronic ST-segment elevation and T-wave inversion in the anterolateral leads was reported in one patient with AHCM, who did not have necrosis of the apex or formation of an apical aneurysm [12]. R-wave voltage and T-wave negativity progressively decreased in magnitude on serial ECGs with associated thallium myocardial perfusion defects detected at long-term follow-up [13]. Giant negative T waves were recorded in the ECG of patients with AHCM who were originally suspected of having acute coronary syndromes [14]. What characterises the entire literature on the ECG in AHCM is its descriptive character, its ‘lumping’ approach in considering the ECG in patients with AHCM together with other patients with varying left ventricular distribution of hypertrophy, and the absence of mechanistic speculations as to the reasons for which the ECG in such patients appears as it does.

These two cases presented here, in the context of the ECG literature in patients with AHCM, with the quantitative analysis of the ECGs shown in Table 1, is proposed as a template to be used in serial ECGs recorded in the long-term follow-up of patients with AHCM, for uniform characterisation of the ECGs of such patients and the changes occurring over time.