Concept and diagnosis

Hypertrophic cardiomyopathy (HCM) is usually a familial disease of genetic origin, characterized by alterations in proteins of the myocardial cells leading to myocardial fiber disarray, hypertrophy of the heart, and an increased incidence of sudden death. More than 500 mutations and 9 genes have been described. The more frequent mutations include troponin T (TNNTZ) and beta myosin heavy chain (MYH7).

The diagnosis is suggested by family history and ECG and is confirmed by echocardiography and other imaging techniques (Figure 21.3) (Maron et al. 2006).

The hypertrophy may cause a dynamic obstruction of the left ventricle outflow tract, and on some occasions it leads to DC and heart failure (HF). When the apex is preferentially involved in the cardiomyopathy, the ECG pattern shows typical features (Figure 21.2).

ECG findings (Figures 21.1–21.4 and Table 21.2)

Pathologic ECGs are observed in approximately 95% of cases, although there is no characteristic ECG alteration indicative of a specific mutation.

In contrast to what is observed in the inherited long QT syndrome, in HCM, it is not possible to predict the different mutations based on the ECG changes, and vice versa, except for some types of predominantly apical HCM (Arad et al. 2005).

However, there are some electrocardiographic patterns clearly indicative of HCM, in particular, a large negative and sharp T wave that is typical of apical HCM (Figure 21.2), as well as a narrow and deep Q wave associated with a positive T wave, suggestive of septal hypertrophy (Figure 21.1).

In patients with HCM, especially apical HCM, RS morphology may be observed in V1. This may be diagnosed mistakenly as right ventricular hypertrophy, but is in fact caused by septal hypertrophy. Thanks to the relationships between ECG and magnetic resonance imaging (MRI), it has become possible to locate the more hypertrophic areas with the ECG (Dumont et al. 2006).

Patients frequently show ECG signs of left ventricular enlargement, which are in some cases very characteristic (Figure 21.2). However, sometimes are impossible to distinguish from those found in other heart diseases. In these cases, imaging techniques play a major role in establishing the correct diagnosis (Figure 21.3).

The QRS voltage is usually increased with often clear criteria of LVH (Figure 21.2). However a low voltage associated with a higher incidence of DC during follow‐up may be seen (Ikeda et al. 1999) (Figure 21.4). Fragmentation of the QRS (fQRS) has been proved to be a predictor of poor evolution and arrhythmias in patients with HCM (Femenia et al. 2013).

At times the ECG alterations are observed before the echocardiogram shows any change. Therefore, an abnormal ECG may be the only evidence suggesting the presence of HCM in a patient’s relatives, or may oblige us to rule it out when it is a casual finding.

An increased interval T wave peak/T wave end may be a more significant risk marker of torsades de pointes ventricular tachycardia (VT) than the QT dispersion or even the corrected QT (QTc) (Yamaguchi et al. 2003).

Often patients with HCM present with arrhythmias in the ECG. The most frequent supraventricular arrhythmia is atrial fibrillation (≈10% of patients) (Britton et al. 2017). The resulting loss of the atrial contribution to the filling of a hypertrophied and stiff left ventricle results in clinical deterioration. The presence of premature ventricular complexes (PVCs) is also common; they are found in more than three‐quarters of patients wearing a Holter device. Runs of non‐sustained VT are found in one‐quarter of patients and its presence has prognostic implications. However, the presence of sustained VT is infrequent.

Very often, different types of blocks, especially intraventricular blocks (left bundle branch block, LBBB), are present in advanced cases.

Clinical implications

Most patients with HCM will likely develop left ventricular outflow obstruction (Maron 2010), although a clear dynamic pressure gradient in the left ventricular outflow tract is only seen in ≈30%. Some patients with HCM present with predominant apical involvement, which is more frequently observed in Japan (Suzuki et al. 1993).

Often, patients with HCM present with progressive dyspnea, especially after 40–50 years, due to diastolic dysfunction. Sometimes it is related to the appearance of atrial fibrillation. However, only about 10–15% of HCM patients will develop DC. The underlying physiopathologic mechanism that explains this evolution is not known with certainty. However, it has been shown that at 10‐year follow‐up, the incidence of HF is higher in patients with low‐voltage QRS complexes (SV1 + RV6 < 35 mm) (Figure 21.4). This is probably because the low voltage is a marker of increased fibrosis (Ikeda et al. 1999).

The few cases with normal ECG have a better prognosis (McLeod et al. 2009), even though some exceptions have been found in patients with troponin T alterations, family history, and evidence of fibrosis by MRI (see below).

The differential diagnosis with athlete’s heart constitutes an interesting challenge. There are clinical, ECG, and echocardiographic data on which we could base our differential diagnosis (Maron et al. 1981). If necessary, other techniques may be used to diminish the doubtful cases (gray zone in Figure 21.5) (Bayés de Luna et al. 2000; Zhang 2014).

Sudden death is the most important risk in this patient population. The yearly mortality rate is around 1%. Sudden death usually occurs during exercise due to a sustained VT leading to ventricular fibrillation (VF). This is the most common cause of sudden death in athletes. However, based on the experience of Maron (2010), more than 30 years may elapse before another cardiac arrest occurs. The most useful main risk factors of sudden death (McKenna and Behr 2002; Maron 2003, 2010) are:

• familial history of sudden death;
  
• personal antecedents of unexplained syncope;
  
• multiple‐repetitive non‐sustained VT in Holter recordings;
  
• abnormal blood pressure response during exercise testing;
  
• massive right ventricle hypertrophy ≥20 mm, and especially ≥30 mm.

The presence of two, or even one for some authors (Maron 2010), of the abovementioned factors, especially when accompanied with genetic alterations (especially troponin T mutations), is associated with an increased risk of sudden death and requires implantable cardioverter defibrillator (ICD) implantation. Meanwhile, the absence of the abovementioned risk factors, especially family history of sudden death in patients older than 50–60 years, is indicative of a better prognosis.

In HCM, as happens in all other inherited heart diseases described in this chapter, the advantages of ICD implant always have to be balanced with the risk of complications (inappropriate shocks, infections, etc.) (Bayés de Luna and Baranchuk 2017).

Concept and diagnosis

We can only speak about long QT syndrome when a patient with apparent good health presents with a nonacquired long QT interval with syncopal attacks or recovered cardiac arrest due to torsades de pointes VT often leading to sudden death, or a family history of this syndrome.

The long QT syndrome is genetic channelopathy characterized by QTc prolongation in ECG and propensity to ventricular tachyarrhythmias (TdPVT, VF) leading to syncopal episodes and/or SCD. In about 10–15% of cases, QTc might remain within normal limit and in about 50% of cases, it will be categorized as borderline (between 440 and 470 ms). Table 21.5 lists ECG changes observed in the LQTS (Moss et al. 1985; Moss and Kan 2005).