Clinical and necropsy findings in 10 dogs with a spontaneous primary hypertrophic cardiomyopathy are described. Each dog had marked cardiac hypertrophy, and 8 dogs had disproportionate thickening of the ventricular septum with respect to the left ventricular free wall (compared with dogs with normal hearts or with cardiac hypertrophy due to acquired or congenital heart disease). Septal:free wall thickness ratios in the 10 dogs ranged from 1.1 to 1.5; 6 had ratios greater than or equal to 1.3. However, marked cardiac muscle cell disorganization in the ventricular septum, characteristic of patients with hypertrophic cardiomyopathy, was present in only 2 of the 10 dogs. Death occurred most commonly while the dogs were under anesthesia during the course of operative procedures (5 dogs) or suddenly and unexpectedly in animals without previous symptomatic manifestations of cardiac disease (3 dogs). Four dogs had clinical signs of congestive heart failure, including 2 with marked cardiac decompensation. In addition, 2 of these 4 dogs with heart failure and 1 dog without previous symptoms (that died during a noncardiac operation) manifested complete heart block. It is conceivable that dogs with spontaneous hypertrophic cardiomyopathy may prove useful in the future investigations of the clinical, hemodynamic, and pathologic features of this disease in humans.

Hypertrophic cardiomyopathy in the dog.

Two siblings with hypertrophic cardiomyopathy developed spontaneous complete heart block requiring permanent pacemaker implantation at similar ages (29 and 33 years). The clinical, morphological, and haemodynamic expressions of hypertrophic cardiomyopathy differed considerably in these two patients. The sister had severe functional limitation due to dyspnoea, pronounced and diffuse left ventricular hypertrophy (maximum ventricular septal thickness of 41 mm), and left ventricular outflow obstruction (peak subaortic gradient of 75 mm Hg under basal conditions). In contrast the brother was symptom free, had only modest left ventricular hypertrophy which was confined to the anterior ventricular septum (maximal thickness of 16 mm), and had no echocardiographic evidence of subaortic obstruction. These dissimilar findings in siblings with hypertrophic cardiomyopathy suggest that the predisposition to develop complete heart block was probably genetically transmitted, although it was unrelated to the phenotypic and clinical expression of the disease.

https://heart.bmj.com/content/heartjnl/55/5/469.full.pdf

Familial spontaneous complete heart block in hypertrophic cardiomyopathy.

Cardiac anatomy and rhythm were evaluated in the fetuses of 18 pregnant women (between 20 and 42 weeks of gestation) referred because of abnormal fetal heart rate or rhythm. Utilizing a 3 MHz two-dimensional scan head with M-mode capability, M-mode recordings were obtained at paper speeds of 50 and 100 mm/s from 16 fetuses. The arrhythmia of two fetuses was diagnosed using two-dimensional echo alone. Semilunar and atrioventricular valve opening and closing points, A waves, plus ventricular wall motion were used for timing purposes; and heart rate and rhythm were determined. Diagnoses made were atrial premature beats n = 3, ventricular premature beats n = 3, congenital heart block n = 4, supraventricular tachycardia n = 3, sinus bradycardia n = 1, and blocked atrial beats n = 1. In three fetuses no arrhythmia was identified. Cardiac anatomy was normal in 16 fetuses, with two (congenital heart block) felt to have univentricular hearts. Fourteen pregnancies went to term, two were delivered prematurely, and two fetuses with congenital heart block were stillborn. In three fetuses arrhythmia was confirmed during labor by fetal scalp electrode. Arrhythmia was absent after birth in 11 of 16 infants, with congenital heart block persistent in two infants, and supraventricular tachycardia, atrial premature beats, and blocked atrial premature beats remaining in one each. Intervention with medical management was attempted in four pregnancies, with successful termination of arrhythmia supraventricular tachycardia) in two fetuses. We conclude that combined two-dimensional M-mode capability is useful in the diagnosis of fetal rhythm disturbances, and perhaps in the selection of timing, and mode of intervention.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/clc.4960080102

Two-dimensional and M-mode echocardiographic evaluation of fetal arrhythmia.

A 25-year-old white female had idiopathic hypertrophic subaortic stenosis proved by catheterization. The ECG revealed left bundle branch block. Electrophysiologic studies revealed normal PA and AH intervals, but the HB interval was prolonged (70 msec). The width of the His spike was 20 msec. A clear, reproducible split His potential was demonstrated with the atrial extrastimulus technique. Because the patient was symptomatic, a permanent pacemaker was inserted. One week later the patient died suddenly. Autopsy revealed an enlarged heart with a markedly thickened and sigmoid ventricular septum and a small and coarsely trabeculated lumen. Histologically the common bundle was situated on the right side of the septum. It was intact at its origin, but showed fibrotic changes more distally. The beginning of the left bundle branch was markedly disrupted as it traversed the septum. The right bundle was moderately fibrosed. There was excellent correlation between the electrocardiographic and electrophysiologic findings and the findings in the conduction system. The cause of the sudden death was related either to the outflow obstruction or to an arrhythmia, or both.

Idiopathic hypertrophic subaortic stenosis with split His bundle potentials. Electrophysiologic and pathologic correlations.

Hypertrophic cardiomyopathy is a primary myocardial disease characterized anatomically by left ventricular (LV) asymmetric hypertrophy and pathophysiologically by normal or even supernormal systolic ejection performance contrasting with impaired diastolic function. Altered ventricular relaxation tends to reduce the contribution of rapid ventricular filling to total LV filling volumes. Consequently, the contribution of left atrial (LA) contraction can be significantly increased. In some patients LV filling, and thus stroke volume, critically depend upon atrial systole. These data may have important clinical implications especially in patients treated with permanent cardiac pacing. Preserving a fully efficient LA contribution to LV filling is probably a key point in those patients.

Importance of Atrial Contraction in Hypertrophic Obstructive Cardiomyopathy: Implications for Pacing Therapy

A young man with IHSS who developed complete heart block was successfully treated with a permanent pacemaker. Echocardiography and other noninvasive techniques showed marked cycle-to-cycle variation in the evidence of subvalvular obstruction which decreased markedly when atrial systole preceded the ensuing paced complex by an appropriate interval. Because cycle length and therefore afterload were constant, it is concluded that diminished obstruction resulted from augmented ventricular end-diastolic volume produced by atrial contraction. The mitral valve echocardiogram showed unusual movements in diastole dependent upon the timing of atrial systole. Early reopening of the leaflets was a direct result of atrial contraction when the P waves were appropriately timed in presystole, whereas late reopening was passive and a result of ventricular filling in mid-diastole. Variations in intensity of the first heart sound correlated with the position of the mitral valve leaflets at the onset of ventricular systole.

A S Mitha

Papers

Complete heart block in a case of idiopathic hypertrophic subaortic stenosis: noninvasive correlates with the timing of atrial systole.