4. Cardiac Resynchronization Therapy in a Patient with QRS Duration Between 120 and 150 Milliseconds

The ECG showed sinus rhythm to be 80 bpm, normal atrioventricular conduction (PR interval, 160 ms), typical LBBB with a QRS duration of 135 ms, and a QRS axis of −35 degrees (Figure 4-1).

The LBBB is typical, with a QRS of 120 ms or greater; broad, notched, or slurred R wave in the lateral leads; absence of Q waves in leads I, V₅, and V₆; an upstroke of the R wave greater than 60 ms in leads V₅ and V₆; and ST and T waves opposite to the QRS polarity.

M-mode analysis of the left ventricle in parasternal long-axis view revealed a left ventricular end-diastolic diameter of 55 mm and a septal flash (Figure 4-2, A). LVEF was measured at 33% using the biplane Simpson method (see Figure 4-2, B). A mild mitral regurgitation also was observed (not shown). The atria were not dilated (diameter 3.2 cm and area 15 cm²).

Although left ventricular function is impaired, the left ventricle is not dilated (<33 mm/m²).

On the echocardiogram, the pulmonary preejection time was measured from the beginning of QRS complex to the beginning of the pulmonary flow velocity curve recorded by pulse-wave Doppler in the left parasternal view at 85 ms (Figure 4-3, A). The aortic preejection time measured from the beginning of QRS complex to the beginning of the aortic flow velocity curve recorded by pulse wave Doppler in the apical five-chamber view was 183 ms (Figure 4-3, B). The intraventricular mechanical delay was 98 ms, demonstrating interventricular dyssynchrony. Major atrioventricular dyssynchrony was demonstrated by left ventricular filling time over the RR cycle length ratio less than 40% (128/709 ms = 18%) (Figure 4-3, C). The apical four-chamber view showed (in red) the delayed motion of the anterolateral left ventricular wall (Figure 4-3, D). Delay between septal (red arrow) and anterolateral (yellow arrow) left ventricular walls of 301 ms demonstrated intraventricular dyssynchrony (Figure 4-3, E).

Echocardiography demonstrated mechanical dyssynchrony at the atrioventricular, interventricular, and intraventricular levels. Particularly, the intra–left ventricular dyssynchrony is extremely severe, with very late activation of the lateral wall.

Given the fact that the most common cause of left ventricular dilation is represented by coronary artery disease, a coronary angiography should always be performed to rule out coronary stenosis (an exercise test often is not helpful in patients with an LBBB pattern on the ECG). Usually, significant stenosis of the left anterior descending artery or of more than two other arteries is necessary to induce cardiomyopathy.